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Understanding the drought phenomenon: the role of definitions.
Abstract
Numerous definitions of drought are reviewed to determine those characteristics scientists consider most essential for a description and an understanding of the phenomenon. Discusses the far-reaching impacts of drought on society, and suggests that definitions of drought are typically simplistic, and, in that way, often lead to a rather poor understanding of the dimensions of the concept.-from Authors
... Giderek artan ekonomik kayıpların yanı sıra ekosistem kuraklığa bağlı olarak yeniden şekillenmekte ve biyotik üyelerin çok büyük bir kısmı yeniden şekillenen ekosisteme adapte olmaya çalışmaktadır (Ding vd., 2011). Doğal süreçlere bağlı olarak gelişen ve aynı zamanda beşerî faaliyetlerle tetiklenen kuraklık (Wilhite ve Glantz, 1985) en yalın haliyle; doğal su mevcudiyetinin belirli bir süre boyunca bölgesel düzeyde uzun vadeli ortalamanın veya normalin altına düşmesine bağlı olarak gelişen su açığı olarak tanımlanmaktadır (Türkeş, 2012). Kuraklık hidrolojik çevrim sistemindeki yağış ve sıcaklık anomalilerinin yanı sıra antropojen faaliyetler ve bu faaliyetlerin iklim elemanları üzerindeki etkileri ile yakından ilişkili olup oldukça dinamik ve son derece karmaşık bir süreçtir (Sırdaş ve Şen, 2003;Mishra ve Singh, 2010). ...
... Kuraklık hidrolojik çevrim sistemindeki yağış ve sıcaklık anomalilerinin yanı sıra antropojen faaliyetler ve bu faaliyetlerin iklim elemanları üzerindeki etkileri ile yakından ilişkili olup oldukça dinamik ve son derece karmaşık bir süreçtir (Sırdaş ve Şen, 2003;Mishra ve Singh, 2010). Dünyanın herhangi bir bölgesindeki su açığını temsil eden kuraklığın meteorolojik, hidrolojik, tarımsal ve sosyoekonomik boyutları bulunmaktadır (Wilhite ve Glantz, 1985;Türkeş, 2017;İrcan ve Duman 2021). Özellikle negatif yağış ve pozitif sıcaklık anomalileri ile kendini gösteren meteorolojik kuraklığın belirli bir bölgede uzun süre devam etmesi halinde hidrolojik, tarımsal ve sosyoekonomik kuraklıklar birbirleri ile etkileşim halinde gelişim sürecine girmektedir (Wilhite ve Glantz, 1985;Nalbantis ve Tsakiris, 2009;Van Loon, 2015). ...
... Dünyanın herhangi bir bölgesindeki su açığını temsil eden kuraklığın meteorolojik, hidrolojik, tarımsal ve sosyoekonomik boyutları bulunmaktadır (Wilhite ve Glantz, 1985;Türkeş, 2017;İrcan ve Duman 2021). Özellikle negatif yağış ve pozitif sıcaklık anomalileri ile kendini gösteren meteorolojik kuraklığın belirli bir bölgede uzun süre devam etmesi halinde hidrolojik, tarımsal ve sosyoekonomik kuraklıklar birbirleri ile etkileşim halinde gelişim sürecine girmektedir (Wilhite ve Glantz, 1985;Nalbantis ve Tsakiris, 2009;Van Loon, 2015). Hidrolojik kuraklık; akarsularda, göllerde, rezervuarlarda ve akiferlerde genellikle uzun süren meteorolojik kuraklık akabinde düşük su miktarının belirgin hale gelmesi olarak tanımlanmaktadır. ...
Kuraklık ve yaygın etkileri çağımızın en büyük problemlerinden biridir. Kuraklığa bağlı olarak su kaynakları üzerindeki baskı her geçen gün artmaktadır. Van Gölü Kapalı Havzası, kuraklığın farklı boyutlarının güncel olarak yaşandığı sahalar arasındadır. Bu çalışmada Van Gölü’nün önemli su toplama alanlarından birini drene eden Bendimahi Çayı’ndaki hidrolojik kuraklık araştırılmıştır. Çalışma sahasındaki hidrolojik kuraklığın ve kurak yılların saptanması için Akarsu Kuraklık İndisi (SDI) kullanılmıştır. Elde edilen bulgular akım, sıcaklık ve yağış verileri ile bir arada değerlendirilerek eğilim analizleri gerçekleştirilmiştir. Bu sayede daha anlamlı sonuçlara ulaşılması hedeflenmiştir. Çalışma bulguları kırk ardışık su yılının %48,5’inde hidrolojik kuraklık gerçekleştiğini göstermektedir. Hidrolojik kurak on dokuz su yılı içinde SDI sınıf aralıklarına göre en büyük kuraklığın 2001 su yılına tarihlendiği belirlenmiştir. Akarsu akımlarında aralık, ağustos ve eylül aylarında istatistiksel açıdan anlamlı azalma eğilimleri gerçekleştiği saptanırken, SDI indislerinde anlamlı bir eğilimin varlığı tespit edilmemiştir. Yağışlarda istatistiksel açıdan anlamlı herhangi bir eğilim olmamasına karşın yaz ve kış aylarına ait sıcaklık değerlerinde istatistiksel açıdan anlamlı artış eğilimleri gerçekleştiği saptanmıştır.
... Frequency of occurrence is different at different locations in the world, so the approaches to define the drought also reflects the regional differences as well as ideologically different economic system be it, capitalist or socialist (Wilhite & Glantz, 1985). ...
... According to (Wilhite & Glantz, 1985) drought has two main definitions , Conceptual and Operational. Conceptual definition tries to stick to the traditional idea of the drought where it tries to define the boundary of a concept, where single definition of specific context is tried on defining the current drought and of course this has limitations. ...
... Conceptual definition tries to stick to the traditional idea of the drought where it tries to define the boundary of a concept, where single definition of specific context is tried on defining the current drought and of course this has limitations. Operational drought tries to define the onset, severity and recovery of the drought, for this definition real time data is needed to define the probability of occurrence (Wilhite & Glantz, 1985). For the operational purpose Wilhite and Glantz grouped over 150 definitions and came up with four main types of droughts: Meteorological, Hydrological, Agricultural and Socioeconomic (WMO, 2018). ...
Drought is complex phenomenon. Universally accepted definition of drought is difficult to find in literature. To declare drought we first need to define it? Defining it considering the local context helps in acceptance by the stakeholders. Once we know what is drought as concept, then indicators and triggers are used in defining the drought severity and its extent. Determination of the trigger values of the indicators should be done cautiously. Interpretation of the triggers can be difficult to the decision makers. The drought declaration seems easy with the help of indicators but it is not. The drought declaration is even complex procedure in the developed countries like Australia and USA, even with developed Monitoring and Early Warning system. Because drought indicators and triggers come with issues like incomparability with other indicators, statistical inconsistency, operational limitations when it comes to define onset and end of drought, that makes them difficult to interpret for the decision makers, sometimes decision makers don’t trust the indicators selected at the top level, also stakeholders are sceptical about it. This research studies the drought declaration process of India and in particular the state of Maharashtra. In this research we find how the parallel process is followed by the state of Maharashtra to declare the drought. In this we try to explore why it has to resort to the parallel process? What is the role of the politics in the drought declarations? How the criteria selected and diluted as per the need to include a region in the drought list. The findings have shown the irregularities in the drought declaration in the year 2018-19 as a case study year. This research has gone through the events during the year 2018-19 in order to understand regional reports and public opinions by reviewing the news.
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This research tries to unravel the process of drought declaration in Maharashtra. It aims to know the irregularities in a process. for the betterment of society.
... They frequently describe drought solely based on the degree of dryness and the length of time that has passed since the last rains. The term "climatological drought" refers to a period of more than a specified number of days during which there is no precipitation greater than a specified small amount (Wilhite and Glantz, 1985). ...
... In agricultural climate models, different characteristics of meteorological drought are linked to different aspects of agricultural impacts. These characteristics include lack of rain, deviation from normal, and a variety of meteorological factors such as evaporation (Wilhite and Glantz, 1985). Drought in agriculture is a time of prolonged dryness that affects the moisture status of the soil and prevents the plant growth. ...
... Difficulties in expressing the socioeconomic consequences of drought can be incorporated into definitions that express the characteristics of agricultural, meteorological, and hydrological droughts (Wilhite and Glantz, 1985). It is common for them to be associated with the demand and supply of a particular economic good. ...
Drought is a common worldwide natural catastrophe. Almost one half of the countries in the globe is situated in drought risk zones. Drought has a major impact on agricultural productivity as well as water availability for household and industrial use. Drought has a gradual impact on the country's economy, but it has a long-term impact. Drought is one of the most serious dangers to people's livelihoods and socioeconomic development among natural catastrophes. It occurs less frequently than other dangers, but when it does, it typically impacts a large area for months or years at a time. India is split into 36 subdivisions based on weather. The nation is split into 127 agro climatic zones for agricultural planning and development, based on temperature, rainfall quantity, soil, and cropping pattern. Drought is a common occurrence in India's climate, and it is typically defined by its regional extent, intensity, and duration. It has a gradual beginning, unlike other natural catastrophes, but increases in strength with deadly consequences. This paper reviews about the current status of drought in India especially Maharashtra and offers suggestions to manage the drought in future.
... Generally, droughts are classified into 'meteorological drought,' 'agricultural drought,' and 'hydrological drought' (Wilhite and Glantz 1985). Meteorological droughts are usually caused by insufficient precipitation; agricultural droughts are the result of decrease in soil moisture content, which can lead to crop photosynthesis and transpiration that reduce yields (Hao et al. 2018). ...
... Vicente-Serrano et al. (2012) provided the first global assessment and comparison of different indices for drought monitoring. However, no single index has adequately captured the intensity and severity of drought and its potential impacts on such a diverse group of users (Wilhite and Glantz 1985). ...
The present study assesses the ability of Monsoon Mission CFSv2-T382 initialized at 4-month and 2-month leads (Feb IC and Apr IC hindcast) to simulate the short-term drought during the Indian Summer Monsoon (June to September). The rainfall-based standardized precipitation index (SPI) averaged over the Indian land region showed significant skills for the 1981–2017 hindcast period for both the ICs. However, the spatial distribution of the skill is moderate and is limited to some regions, and varies within the season. Category-wise forecasts indicate that even with strong rainfall bias and moderate false alarm ratio, model hindcasts have a better detection ratio, hit rate, etc., demonstrating the model’s usefulness for predicting the all-India drought. The observed SPI over the entire India during the month of June has a strong positive (negative) relationship with soil moisture (surface temperature) over India, along with warm (cold) SST anomalies in the northern Indian Ocean (north tropical Atlantic Ocean). The SST anomalies associated with El Nino Southern Oscillation (ENSO) dominate the drought towards the end of the monsoon season. However, SPI simulated by model hindcasts has a stronger relationship with ENSO throughout the season. The homogenous region-wise skill analysis and teleconnections of SPI explain its scattered skill over Indian land regions. The observed regional surface temperature and soil moisture have a strong 1–2-month lead relationship with SPI in all homogenous regions, and forcing from ENSO is evident for WCI and SPInd only. The model overestimates the simultaneous ENSO relationships for all the homogenous regions, while the lead role of moisture, surface temperature, and north tropical Atlantic SST is under-predicted. WCI and SPInd regions have a moderate lead relationship with soil moisture and surface temperature along with ENSO teleconnection, resulting in improved skill compared to other subdivisions of India. The study shows that further improvement of the regional scale skill of CFSv2 for capturing SPI is possible mainly with the regional scale improvement of land surface processes and its lead teleconnection with SPI in the model.
... Drought is a naturally occurring climate phenomenon that impacts human and environmental activity globally and is considered to be one of the costliest and most widespread of natural disasters (Smith & Katz, 2013;Below, Grover-Kopec & Dilley, 2007). In terms of negative impacts, droughts are currently ranked number one (Wilhite & Glantz, 1985, Guha-Sapir et al., 2012. Compared to other natural disasters such as floods, hurricanes, earthquakes and epidemics, droughts are very difficult to predict; they creep slowly and last longest. ...
... However, lack of definite characteristics of drought is a major dilemma for the scientific and policy-making community and is preventing a detailed understanding of the drought phenomenon. The absence of an accurate and precise definition of drought has been an obstacle to understanding drought, which has led to indecision and inaction on the part of the individuals concerned managers, policy-makers (Wilhite & Glantz, 1985;Wilhite et al., 1986). ...
Drought is a complex environmental phenomenon that affects millions of people and communities all over the globe and is too elusive to be accurately predicted. This is mostly due to the scalability and variability of the web of environmental parameters that directly/indirectly causes the onset of different categories of drought. Since the dawn of man, efforts have been made to uniquely understand the natural indicators that provide signs of likely environmental events. These indicators/signs in the form of indigenous knowledge system have been used for generations. The intricate complexity of drought has, however, always been a major stumbling block for accurate drought prediction and forecasting systems. Recently, scientists in the field of agriculture and environmental monitoring have been discussing the integration of indigenous knowledge and scientific knowledge for a more accurate environmental forecasting system in order to incorporate diverse environmental information for a reliable drought forecast. Hence, in this research, the core objective is the development of a semantics-based data integration middleware that encompasses and integrates heterogeneous data models of local indigenous knowledge and sensor data towards an accurate drought forecasting system for the study areas. The local indigenous knowledge on drought gathered from the domain experts is transformed into rules to be used for performing deductive inference in conjunction with sensors data for determining the onset of drought through an automated inference generation module of the middleware. The semantic middleware incorporates, inter alia, a distributed architecture that consists of a streaming data processing engine based on Apache Kafka for real-time stream processing; a rule-based reasoning module; an ontology module for semantic representation of the knowledge bases.
... Droughts are categorised into 5 groups, namely meteorological, hydrological, socio-economic, ecological and agricultural (Tate and Gustard, 2000;Wilhite and Glantz, 1985). This study makes reference to meteorological and agricultural droughts which are most relevant droughts from a crop production perspective. ...
... This study makes reference to meteorological and agricultural droughts which are most relevant droughts from a crop production perspective. A meteorological drought is when there is lack of precipitation coupled with presence of dry winds and high temperatures over an extended period of time (Tate and Gustard, 2000;Wilhite and Glantz, 1985). An agricultural drought occurs when there is not enough moisture to support crop production or grass production on rangelands (Mannocchi, et al., 2004). ...
Smallholder farmers in communal areas of Zimbabwe frequently
face challenges of low agricultural productivity and food insecurity, which lead to cases of abandonment of agricultural land because of low and erratic rainfall. Analysis of the quality of agricultural seasons in communal areas in south-central Zimbabwe across the four agroecological regions (AER II- AER V) on a high to low potential gradient, was undertaken to understand its implications on dry-land maize production, the country ‘s staple food crop. The parameters that were used to assess the quality of the season included variations in mean annual rainfall, onset of rains, length of growing season, total wet and dry days and frequency of droughts. Results showed that mean annual rainfall and length of growing season across the agroecological gradient were suitable for maize production. However, onset of rains was found to have shifted towards end of November leading to early cessation of the rainfall season. Across all the AERs, moisture stress conditions for maize growth were exhibited in 70 % of the growing seasons. Drought years were observed in between 47 – 52 % of a 33-year period. Mid-season dry spells were common in all the AERs, and occurred in almost every other season. The dry spells commonly occurred during the peak period for crop growth. Data from this study showed that the quality of agricultural seasons was poor for maize crop production in both low and high potential areas. The resultant poor maize yields in rain-fed farming systems contributed to increased food insecurity, and abandonment of agricultural land. Further studies are required to ascertain the viability of growing alternative crops and water conservation technologies to make optimal use of the limited available moisture.
... vulnerability is dynamic; (de 110 Ruiter and ). Time is an important element in the development of drought and drought impacts, as recognised by previous studies (Hall and Leng, 2019;Tijdeman et al., 2022;Wilhite and Glantz, 1985;WMO, 2021) and time characteristics have been studied empirically in the separate systems (see some examples in Table 1). In the next sections, we explore and discuss the concept 180 of memory shaping drought over time from different perspectives: hydrology, ecology, and social science. ...
... Short-term crisis management is most common, including emergency relief, such as water trucks and cash transfers, targeted at specific areas and affected groups 460 (Barendrecht et al., 2024;Wilhite, 2017). However, governments often deal with each drought as a "new" or unique event, possibly because of a low memory of "creeping disasters" like drought (Ulibarri and Scott, 2019; Wilhite and Glantz, 1985) (illustrated in the hydro-illogical cycle; Fig. 3b, blue line). This makes it less likely that long-term proactive measures are implemented for drought, compared to other natural hazards. ...
Droughts are often long lasting phenomena, without a distinct start or end, and with impacts cascading across sectors and systems, creating long-term legacies. Nevertheless, our current perception and management of droughts and their impacts is often event-based, which can limit the effective assessment of drought risks and reduction of drought impacts. Here, we advocate for changing this perspective and viewing drought as a hydro-eco-social continuum. We take a systems theory perspective and focus on how “memory” causes feedback and interactions between parts of the interconnected systems at different time scales. We first discuss the characteristics of the drought continuum with a focus on the hydrological, ecological, and social systems separately; and then study the system of systems. Our analysis is based on a review of the literature and a study of five cases: Chile, the Colorado River Basin in the US, Northeast Brazil, Kenya, and the Rhine River Basin in Northwest Europe. We find that the memories of past dry and wet periods, carried by both bio-physical (e.g. groundwater, vegetation) and social systems (e.g. people, governance), influence how future drought risk manifests. We identify four archetypes of drought dynamics: Impact & recovery; Slow resilience-building; Gradual collapse; and High resilience, big shock. The interactions between the hydrological, ecological and social systems result in systems shifting between these types, which plays out differently in the five case studies. We call for more research on drought pre-conditions and recovery in different systems, on dynamics cascading between systems and triggering system changes, and on dynamic vulnerability and maladaptation. Additionally, we argue for more continuous monitoring of drought hazards and impacts, modelling tools that better incorporate memories and adaptation responses, and management strategies that increase social and institutional memory to better deal with the complex hydro-eco-social drought continuum and identify effective pathways to adaptation.
... To better comprehend the complexities of drought, researchers have categorized it into four broad types [8]. Meteorological drought occurs when a region experiences a prolonged absence of precipitation. ...
Drought prediction is a crucial task in climate-related forecasting, with significant implications for agriculture, water resource management, and disaster preparedness. In this study, we present a Long Short-Term Memory (LSTM) neural network model to predict drought using the Standardized Precipitation Index (SPI) values from multiple regions, namely Sreemangal, Jessore, and Syl-het. The dataset was preprocessed, and the data was split into training, testing, and validation sets. The LSTM model was trained with a custom R-squared metric to evaluate its performance. Additionally, we compared the LSTM model's performance against traditional statistical models, including Multiple Linear Regression (MLR), Random Forest, and a calculated value from another model. The results demonstrated that the LSTM model exhibited superior predictive accuracy, achieving higher R-squared values and lower mean squared error (MSE) and mean absolute error (MAE) values compared to the other models. This study highlights the effectiveness of the LSTM model in drought prediction and its potential to enhance decision-making in drought-prone regions. 1
... Consequently, comprehending the characteristics of drought and its repercussions plays a crucial role in the effective management of water resources (Tsakiris et al., 2013). Droughts can be classified into four distinct types: meteorological, hydrological, agricultural, and socioeconomic droughts (Wilhite and Glantz, 1985). In the context of hydrological drought, the significance of groundwater is underscored as a crucial natural resource, contributing around 50 % of the world's drinking water and satisfying 20 % of its irrigation needs (Guo et al., 2021). ...
In recent years, the escalating impact of climate change, coupled with growing concerns regarding groundwater drought, has underscored the critical importance of analyzing hydrological trends. This is a foundational step in advancing effective water resource planning and management. This study presents a regional investigation of groundwater and meteorological droughts in the UK, utilizing the Standardized Groundwater Index (SGI) and the Standardized Precipitation Index (SPI). The analysis encompasses drought duration and an evaluation of the correlation between the SGI and SPI. Subsequently, the seasonal Mann-Kendall (MK) test and the Bayesian Changepoint Detection and Time Series Decomposition (BEAST) algorithm were employed to assess overall trends for both SGI and SPI. Additionally, these methods were utilized to pinpoint trend and seasonal abrupt changes within the time series of both indices.
The seasonal MK test revealed statistically significant trends in many SGI stations across the UK, spanning from Northern Scotland down to the South of England, encompassing both increasing and decreasing trends. Additionally, the MK test showed slightly positive trends at the low SPI time scale, though these were not statistically significant. In contrast, more consistent and significant increasing trends were observed throughout the entire UK, except for Northern Scotland, which exhibited negative trends. Despite indications of a progressively more humid UK, the BEAST analysis enabled the detection of decreasing abrupt changes in trends. These changes result in sudden transitions from wet to dry conditions, which can be challenging to identify using the MK test alone. However, BEAST revealed both positive and negative abrupt changes across the entire UK, as well as positive or negative variations in seasonality. This suggests a high degree of variability in seasonal patterns. In summary, this study provides a detailed assessment of groundwater and meteorological drought trends and abrupt changes, considering the impact of climate change on various regions of the UK.
... Drought is one of the extreme climatic conditions caused by extreme meteorological and hydrological events. There are many definitions for drought (McKee et al., 1993;Palmer, 1965;Redmond, 2002;Wilhite, 2000aWilhite, , 2000bWilhite et al., 1985). Drought is generally defined as a longterm dry conditional that causes hydrological imbalance in a region (Eslamian et al., 2017). ...
The study of drought, one of the many problems caused by climate change, enables the planning of water use and water resources. The increase or decrease in drought severity, which is one of the drought parameters, is an important source of information in terms of predetermining the consequences that may arise due to drought. In this study, drought analysis was conducted for 1-, 3-, 6-, 9- and 12-month time periods with the Standard Precipitation Index (SPI) using long-term precipitation data of four stations in the Tigris River basin from 1960 to 2022. Drought duration and severity series were obtained from drought index values, and the trends of drought severity series were calculated with Mann-Kendall (MK) and Innovative Trend Analysis (ITA) tests. According to the results, the ITA test was found to be more sensitive in detecting trends in drought severity series compared to the MK test. According to the MK test, drought did not show a significant increase or decrease. On the other hand, according to the ITA test, drought increased at 1- and 12-month scales at Siirt and Batman stations, respectively, and at 1- and 12-month scales at Diyarbakır station. Drought increased in all time periods at Mardin station.
... Before delving into an analysis of drought periods in the specified area, it's crucial to recognize the comprehensive classification of drought proposed by Wilhite [25]. They categorize drought into four main types: meteorological (extended deficit in precipitation), agricultural (shortfall in soil moisture), hydrological (decrease in water flow or groundwater storage), and socio-economic [26]. Understanding this classification framework provides a foundational understanding for our analysis. ...
Extreme climate change phenomena are a global reality with major repercussions on hydrosystems. Drought is particularly concerning in the southern Mediterranean region, threatening water availability and related behavior. Morocco, located in North Africa and the southern Mediterranean, is highly exposed to climate change and its consequences, particularly drought. This study aims to investigate the impact of climate variability and drought characteristics on the Saïs plateau and the Middle Atlas region, using statistical and spectral indices. By analyzing annual variations in precipitation and using the Standardized Precipitation Index (SPI) and normalized difference water index (NDWI) to elucidate the temporal dynamics of water, this study highlights significant irregularities in precipitation patterns between wet and dry years, offering insight into the severity and occurrence of drought at different altitudes. In addition, the study uses the normalized difference water index (NDWI) to elucidate temporal water dynamics, revealing cyclical patterns of water availability and identifying regions sensitive to hydrological activity or drought. Furthermore, thanks to a correlation analysis between the NDWI and the SPI12 index, the study highlights the complementary relationship between spectral and statistical indices in the assessment of drought phenomena. The results show a significant difference in precipitation between the Middle Atlas and the Sais Plateau, with the Middle Atlas receiving around double the precipitation. From 1980 to 1985, drought was followed by even drier conditions until 1995, with sporadic wet years such as 1995 and 2002. During the 1980–1994 period, a persistent drought was observed until 1995, when precipitation picked up again, with notable records in 2009–2010. Positive NDWI values, with marked peaks between 2010 and 2012, indicate periods of high-water content, while negative values, such as those in 1995, 2003, and 2006, denote periods of low water content or drought.
... This contradiction is primarily an artifact of definitions. Wilhite and Glantz (1985) refer to a similar situation in Brazil when an apparent disagreement between policy-makers and the public on the one hand and meteorologists on the other, took place regarding the duration and severity of a drought. It was suggested that the semiarid region of northeast Brazil had been affected by a five year drought, while the meteorologists noted that only two years of the fiveyear period could have been classified as drought. ...
Faragó T.; S. Dunay; Cs. Nemes, 1990: Meteorological and agro-economic aspects of recent drought episodes in Hungary. Időjárás, 94:1, pp.
... There are many conceptual definitions of drought in the scientific literature. Quite a few of these definitions have been reviewed by Wilhite and Glantz (1985), by Andreeva and Sazonov (1987), Girskaya and Sazonov (1979) and by the WMO (1975), but according to the authors of the first work (see also Sadowski, 1984 andBagrov, 1986) the lack of a precise (and objective) definition of drought can be an obstacle to understanding this phenomenon. ...
Proper quantification of drought events is required for either their comparative spatial and temporal evaluation or for relevant predictability studies. Drought indices appear to be the simplest tools in drought analysis. The objective of this paper is to collect more or less "popular" indices, and to compare them as to their theoretical and numerical effectiveness. Indices are classified into four groups: precipitation indices, supply/demand (water balance) indices, soil moisture indices, and "recursive" indices. For each group, a few typical expressions are given and analyzed for-their performance and comparability. Some empirical relations are established among the different indices. Those indices proved to be of highest utility in the delineation of meteorologically determined droughts which possess "memory" that is which actual values depend also on preceding values of the related meteorological elements. Such indices are the soil moisture, and Bhalme-Mooley or Palmer indices. Results are illustrated for.some.recent.drought.events.in Hungary.
... Drought, perhaps, is one that draws the most attention as it usually has an adverse impact on agricultural production. There now exist many definitions of drought (see, for example, Wilhite and Glantz, 1985), and these definitions are often specific to a region or to an agricultural activity. Not only a specific drought within a given year, but successive years of drought as well, can be identified as an individual extreme event (Karl and Quayle, 1981;Karl, 1983;WMO, 1986; see also the analysis of the recent drought episodes in Hungary by Dunay et al., 1988). ...
Analysis of and coping with the extreme phenomena and occasional extreme events of the surrounding natural environment is of great importance for societies. Different aspects of the investigation of such meteorological events are dealt with from a conceptual point of view. Among others, the relative character of the occurrence of extreme values, their relation to the climatic variability, the limitations concerning the application of theoretical methods of analysis, the role of case studies and case-scenarios are considered. Because of the complexity of these problems and the potential significant socioeconomic impacts, in the authors' opinion, further interdisciplinary research is needed on extreme meteorological events in order to improve society's ability to cope with them.
... Moreover, the precipitation deficit is not a reliable indicator of extreme drought 56 . Extreme drought is often determined by drought intensity, primarily driven by temperature 57 . Higher air temperatures can intensify evaporative demand, leading to increased evaporative losses from the surface and higher soil moisture deficits 58 . ...
The intensification of compound hot-dry events due to climate change is a pressing concern, underscoring the need for precise analysis. However, the impact of different dry indicators on projections of these events has not been quantitatively evaluated, nor has its importance been compared with other sources of uncertainty. Here we examine the sensitivity of projected changes in compound hot-dry events to different dry indicators. We use data from 22 Coupled Model Intercomparison Project Phase 6 (CMIP6) models to characterize global dry conditions based on precipitation, runoff, soil moisture, and a multivariate index combining these variables through trivariate copulas. Our findings reveal large differences in projected changes in the likelihood of compound hot-dry events across different dry indicators. While model uncertainty remains the primary source of uncertainty for compound hot-dry event projections, the uncertainty associated with dry indicators is also substantial, surpassing scenario uncertainty in specific regions.
... The creeping nature of drought makes it difficult to precisely determine its onset and end. Meteorological, hydrological, agricultural, and socioeconomic droughts directly affect agriculture through declining crop yields and livestock production, thereby increasing food insecurity and livelihood susceptibility [2,[36][37][38]. It disrupts the supply chain, impacts businesses and essential services, and accelerates land degradation and the depletion of water resources. ...
Globally, drought is occurring more frequently today, which is considerably affecting rural households’ agricultural productivity and socioeconomic development. Understanding households’ perceptions of drought is thus important for resilience-building work because people act based on their views, and the resilience of people is tied to their views, knowledge, culture, and attitudes. This study analyses the rural households’ perceptions of drought occurrence and its influence on livelihood strategies in northeast Ethiopia. This was achieved through a mixed-methods approach with a concurrent research design. The quantitative data were collected from 354 randomly selected household heads, whereas the qualitative data were collected from purposefully selected household head focus group discussions (FGDs) and key informants. The quantitative data were analyzed using descriptive statistics, whereas the qualitative data were analyzed using thematic data analysis techniques. The results show that climate variability and drought occurrence were perceived by the households as decreasing rainfall, increasing temperature, variations in rainfall onset and cessation, variations in heat waves and cold waves, heavy rainfall events, changes in sporadic rain, a lesser coverage of clouds, and adverse weather events. Within the last 25 years, households have perceived the number of extreme, severe, or moderate droughts to be increasing. Household perceptions of temperature changes match meteorological records, but their perceptions of rainfall changes do not. The drought hampered income sources, brought food shortages, and threatened family well-being. It increased water stress, livestock morbidity and mortality, insect invasions, fire outbreaks, grazing resource depletion, abnormal migration, school dropout rates, and human health problems. The findings have important policy implications to mitigate drought risk, enhance drought adaptation, and develop pathways out of drought vulnerability, so it is worthwhile to harmonize the household perceptions with climate change policy.
... The increased spatial and temporal variability of rainfall and temperature, driven 101 by topographic features, facilitates the emergence of meteorological drought, which 102 serves as the first indication of a temporary deficit of rainfall (Haile et al., 2020; Wilhite 103 and Glantz, 1985). Prolonged meteorological droughts can escalate into agricultural, 104 ...
Drought, a recurring natural phenomenon in South Asia's monsoon climate, presents challenges in delineating its spatiotemporal patterns within complex topographies. This study investigated the impact of the orographic barrier in the rice‐dominated agricultural region of northeastern India and Bangladesh on drought characteristics during 1951–2020, employing the relative Standardized Precipitation Index (rSPI) and relative Standardized Precipitation‐Evapotranspiration Index (rSPEI) across 3‐, 6‐ and 12‐month scales. The results indicate that even in the rainiest region of the world, droughts extend beyond the limits of the dry season inherent in the monsoon regime. These mostly regional droughts exhibit weak correlations with the core of the Indian subcontinent and other parts of Bangladesh. The region's orographic barrier has a greater influence on drought intensity than on frequency. The rSPI index, which depends solely on rainfall, may overestimate drought intensity and frequency in regions with high seasonal/annual rainfall and substantial intermonthly variability. In contrast, the rSPEI index, which depends on both rainfall and potential evapotranspiration (PET), better reflects the spatial variation of drought in complex terrain, identifying the leeward hinterland of the orographic barrier as the most drought‐prone area. The two indices give similar results for drought characteristics away from the barrier. Furthermore, the orographic barrier exerts a negligible influence on the trends in rSPI and rSPEI. Principal component analysis (PCA) highlights the influences of the rainfall coefficient of variation and elevation on rSPI, while the PET coefficient of variation strongly influences rSPEI. Strategies to minimize the adverse effects of drought in complex topography and year‐round cropping should be local and season‐specific. These include using shorter‐growing, drought‐resistant rice varieties and adjusting planting schedules in rain shadow areas during the summer monsoon. These efforts should be complemented by integrating indigenous irrigation methods with modern practices such as roof water harvesting and tube wells in winter.
... We define a drought event as a negative precipitation deviation from the long-term average , during a hydrological year, which spans from October to September (e.g., Wilhite & Glantz, 1985). Additionally, we defined the intensity of drought years according to the Standardized Precipitation Index (SPI) (McKee et al., 1993). ...
Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land‐use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long‐term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long‐term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub‐encroached Mediterranean oak woodlands. Our results also emphasize that the long‐term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.
... Therefore, a universally accepted drought definition has proved elusive, if not unobtainable. Currently, around 150 drought indices exist, each designed to measure a specific phenomenon of drought with their own strengths and limitations [26,57,60]. No drought indices have been designed for human health research, and there is no "best" drought measure for epidemiological applications [15]. ...
Purpose of Review
Drought is one of the most far-reaching natural disasters, yet drought and health research is sparse. This may be attributed to the challenge of quantifying drought exposure, something complicated by multiple drought indices without any designed for health research. The purpose of this general review is to evaluate current drought and health literature and highlight challenges or scientific considerations when performing drought exposure and health assessments.
Recent Findings
The literature revealed a small, but growing, number of drought and health studies primarily emphasizing Australian, western European, and US populations. The selection of drought indices and definitions of drought are inconsistent. Rural and agricultural populations have been identified as vulnerable cohorts, particularly for mental health outcomes.
Summary
Using relevant examples, we discuss the importance of characterizing drought and explore why health outcomes, populations of interest, and compound environmental hazards are crucial considerations for drought and health assessments. As climate and health research is prioritized, we propose guidance for investigators performing drought-focused analyses.
... Drought is a recurrent feature of the arid and semiarid regions, which may lead to depletion of surface and sub-surface water resources, crop failure and reduced food & fodder availability affecting humans, livestock, and wildlife. Drought can be categorized into four types i.e., Meteorological, Hydrological, Agricultural and Socioeconomic drought (Wilhite and Glantz, 1985). Agricultural drought is characterized by poor crop health and a reduction in crop production as a result of soil moisture deficiency due to inadequate rainfall coupled with higher evapotranspiration rates. ...
Remote sensing technology has demonstrated its significant utility in the monitoring and mapping of agricultural drought on a global scale. This study focused on the assessment of agricultural drought in the Saurashtra region of Gujarat, India, utilizing a comprehensive dataset spanning 33 years from Landsat and Sentinel satellites. It employed various vegetation indices, including NDVI (Normalized Difference Vegetation Index), Anomaly Index (NAI), Vegetation Condition Index (VCI) and NDWI Anomaly index (NDWIA), to gauge drought conditions. The performance of these indices was evaluated through the generation of drought severity maps and their correlation analysis with major Kharif crops in the region, specifically cotton and groundnut. The analysis pinpointed major agricultural drought years, such as 1986, 1987, 1991, 2000, 2002 and 2012, which corresponded to substantial crop yield losses ranging from 37% to 76% for cotton and 66% to 95% for groundnut, varying by district. Despite VCI demonstrating equivalent or superior correlations with crop yields (ranging from 0.32 to 0.73 for cotton and 0.33 to 0.75 for groundnut) compared to NAI in various districts, it tended to underestimate drought severities, designating only 2 to 9 drought years for different districts. Consequently, this study recommends revised VCI drought severity thresholds, which enhance the categorization of agricultural drought in terms of severity levels and corresponding yield losses for cotton and groundnut in the Saurashtra region of Gujarat. Furthermore, it underscores the need to establish region-specific drought severity thresholds by identifying the most suitable vegetation index for effective quantification of agricultural drought, thereby facilitating informed drought mitigation measures.
... Drought stands as one of the most prevalent and devastating natural disasters globally, categorised as meteorological, hydrological, agricultural, environmental, or socioeconomic, depending on the type of water scarcity (Wilhite and Glantz, 1985;Zhang et al., 2023aZhang et al., , 2023b. Meteorological droughts (MD) serve as the precursor to all other types of droughts and have the potential to evolve into agricultural and hydrological droughts (HD), ultimately causing socio-economic disasters (Wu et al., 2017;Zhang et al., 2022;Yang et al., 2023). ...
... Droughts have been one of the most frequent natural disasters in the world over the past few decades, posing a serious threat to the security of food production, water supply, and ecosystems [1][2][3][4]. With the increasing impact of climate change, many studies have indicated that the frequency and scope of droughts will expand in the coming century [5][6][7]. ...
Ecological droughts in rivers, as a new type of drought, have been greatly discussed in the past decade. Although various studies have been conducted to identify and evaluate ecological droughts in rivers from different indices, a forecast model for this type of drought is still lacking. In this paper, a numerical weather forecast, a hydrological model, and a generalized Bayesian model are employed to establish a new general framework for the probabilistic forecasting of ecological droughts in rivers, and the Daitou section in China is selected as the study area to examine the performance of the new framework. The results show that the hydrological model can accurately simulate the monthly streamflow with a Nash–Sutcliffe efficiency of 0.91 in the validation period, which means that the model can be used to reconstruct the natural streamflow from the impact of an upstream reservoir. Based on a comparison of ecological drought events from the observed and model-simulated streamflow series, the events from the observed series have a larger deficit volume and a longer duration of ecological droughts after 2014, indicating that human activities may lead to a more severe situation of ecological droughts. Furthermore, due to the uncertainty of precipitation forecasts, a probabilistic precipitation forecast is employed for probabilistic ecological drought forecasting. Compared to the deterministic forecast, the probabilistic ecological drought forecast has better performance, with a Brier score decrease of 0.35 to 0.18 and can provide more information about the risk of ecological droughts. In general, the new probabilistic framework developed in this study can serve as a basis for the development of early-warning systems and countermeasures for ecological droughts.
... Drought is an environmental calamity that can lead to a lack of drinking water for humans and livestock, reduced crop production, and increased economic costs, with considerable damaging effects on humankind (Dracup et al. 1980;Wilhite 2000). Usually, drought can be classified into four different types: meteorological, agricultural, hydrological, and socioeconomic (Van Loon 2015; Wilhite and Glantz 1985). The first three types of droughts are caused by a deficiency of precipitation, soil moisture, and water resources (surface or groundwater), respectively (Mishra and Singh 2010;Zhu et al. 2016). ...
Understanding the relationship between hydrological and meteorological drought in drought-prone regions is critical for proper reservoir management. This study presents a novel multiscale framework for investigating the associations between hydrological and meteorological drought based on the Time-Dependent Intrinsic Correlation (TDIC) method. Firstly, the characteristics of short, medium and long term standardized precipitation index (SPI) and the standardized runoff index (SRI) of the Wadi Mina basin (Algeria) have been analyzed based on data from 6 rainfall and hydrometric stations. Then an Improved Complete Ensemble Empirical Mode Decomposition with adaptive noise (ICEEMDAN) method is used to decompose the most correlated SPI and SRI series to different scales. A stronger association between the two types of droughts is evident in the low-frequency trend component regardless of the station, but their evolution pattern does not remain the same. Subsequently, a TDIC based running correlation analysis is performed between the modes to examine the SPI–SRI associations over the time domain and across the time scales. TDIC analysis has proven the dynamic behavior in the SPI–SRI associations bearing frequent alterations in nature and strength across the process scales and along the time domain. In general, at the intra-annual scales the SPI–SRI correlations are mostly weak positive with localized alterations to negative along the time domain, whereas the relationship is dominantly strong positive and long range at inter-annual scales up to 4 years. This dynamic behavior in the SPI–SRI association and the evolution pattern of trend decipher that the rainfall processes are not directly transferred to streamflow drought, but it also gets controlled by many other local meteorological processes.
... Said, A., M., Satispi, E., Samudra, A., A. (2024 However, understanding disasters, especially concerning drought due to uncertain weather conditions leading to reduced rainfall and unsustainable hydrological water availability, has yet to be effectively socialized (Bhaga et al., 2020). Wilhite and Glantz (1985) It is imperative to recognize that managing drought disasters often requires a combination of approaches tailored to the local context, culture, and geographical conditions. Achieving effective and sustainable policy implementation demands collaboration between the government, society, and other relevant stakeholders (Samudra et al., 2023b). ...
Objective: This research aims to analyze the existing drought mitigation policies implemented in East Lombok Regency and evaluate their sustainability and effectiveness. Drought poses a significant threat to East Lombok Regency, Indonesia, potentially impeding sustainable development in the region. Theoretical framework: The study employs the Disaster Risk Reduction Approach as outlined in the Sendai Framework for Disaster Risk Reduction 2015-2030. It involves mapping Drought Disasters as a problem, assessing the Impact of Drought Disasters (Risk), examining the role of Institutions, exploring methods for handling disasters through Drought Emergency Response solutions, addressing Education on drought disasters, and identifying Challenges and Recommendations for the future. Methodology: The research employs a qualitative approach involving the analysis of policy documents, interviews with stakeholders, and field surveys to gather data related to the implemented mitigation efforts. Results: The findings indicate the significance of having a Regional Disaster Management Master Plan to guide mitigation, preparedness, emergency response, and post-disaster recovery. However, it has not been developed in the study area. Current efforts for drought mitigation, preparedness, and emergency response mainly involve routine activities, such as distributing clean water to affected locations, suggesting the need for a more innovative approach. Conclusion: This study concludes that the absence of a Regional Disaster Management Master Plan hinders reactive and coordinated mitigation efforts. The sustainability of these programs is a significant concern and is crucial for establishing a robust strategic foundation for disaster management. Recommendation: The study emphasizes the urgent need to design a comprehensive Regional Mitigation Master Plan. This initiative aims to enhance coordination between institutions, strengthen community capacity, and ensure the sustainability of mitigation efforts. The research contributes to a deeper understanding of the challenges and opportunities in managing potential drought disasters in East Lombok Regency, providing a basis for more effective and sustainable policymaking. Research Implications: The research outlines the implications of formulating policy issues for designing a Regional Disaster Management Master Plan and establishing clearer regulations and Standard Operating Procedures in the future. These findings are crucial for guiding consistent and effective policies, ensuring a more diverse and resilient response to the challenges of recurring drought disasters in East Lombok Regency. Originality/Value: This research delves into the paradigm shift within the field of drought disaster management, which still relies on conservative methods. The study paves the way for new regulatory guidelines by incorporating several crucial points in the draft Regional Disaster Management Master Plan, including Drought Disaster Mitigation Policy, Drought Emergency Response, and Drought Disaster Education. This research contributes new insights to the field, providing a deeper understanding of drought disaster management. A notable challenge is the absence of formulated comprehensive Regional Disaster Management Master Plans by implementers, with the current reliance on temporary regulations established by the Regional Disaster Management Agency.
... Drought is a complex natural hazard which has numerous adverse effects on agriculture, economy, industries, ecology, life and livelihoods of humans, etc. (Wilhite et al., 2007;Edwards et al., 2019;Parsons et al., 2019). Drought is initiated by the meteorological, agricultural, hydrological and socioeconomical (Wilhite and Glantz, 1985). Agricultural drought is referred to as a condition initiated by failure in precipitation leading to the decline in soil moisture and consequent crop failure without any reference to surface water resources. ...
Drought is one of the complex natural hazards having multi-dimensional harmful impacts on agriculture and economy. Evapotranspiration is a good indicator of crop water stress, therefore, an evapotranspiration-based index can be used to monitor the agricultural drought. Standardized Evaporative Drought Index (sEDI) is such an index which is derived from the standardization of the Evaporative Drought Index (EDI) over time. EDI is based on the ratio of actual to potential evapotranspiration. The value of EDI increases with the increase in crop water stress. In this study, sEDI was computed from the MODIS actual and potential evapotranspiration data at 1 km spatial resolution and 16-days temporal interval during kharif crop season over India from 2001 to 2021. The Mann-Kendall trend analysis was also performed for each 16-day time period of the kharif crop season at 10% level of significance. It was found that the sEDI was accurately able to capture the spatiotemporal variation of the historical agricultural drought events over India. Most of the net sown area (64.9-85%) didn't show any trend in sEDI during kharif crop season, while significant increasing as well as decreasing trend was found in approximately 0.3-15.7% and 2.0-34.8% percentage of net sown area across all the time periods, respectively. An increasing trend was mainly found in the southern and eastern parts of India including Gujarat during the early and mid-phase of kharif crop season, whereas, the late-phase had most of the area showing a decreasing trend in drought. This study clearly brought out the spatiotemporal variation of agricultural drought at a finer spatial scale and could help in prioritizing the appropriate water management strategies to mitigate the effects of drought in India.
... Despite the fact that drought is primarily a phenomenon associated with water, it has been studied and defined from a variety of perspectives by a variety of scientific and social sciences fields. There are four main categories of drought, according to (Wilhite and Glantz, 1985 Risks from toxic heavy metal contamination exist for all types of life worldwide. Heavy Metals are any relatively high-density metallic elements that can hurt or be dangerous to cells even at low concentrations (Liu et al., 2019), leading to significant health issues in living things like mutations, nephrotoxicity, endocrine disruption, and other issues (Briffa et al., 2020;Prasad et al., 2022). ...
The world is facing a consistent increase in human population and a noticeable decrease in cultivable lands due to soil salinization, abrupt climatic changes, and less rainfall. These problems have increased the importance of finding ecologically sustainable solutions to ensure global food security. Using plant growth-promoting rhizobacteria (PGPR) can be advantageous to enhance plant productivity and safeguard against environmental stresses. They may assist the plant by fixing atmospheric nitrogen, nutrient recycling, solubilizing phosphate, iron sequestration by siderophore formation, and production of phytohormones like Indole-3-Acetic Acid (IAA) and 1-Aminocyclopropane-1-Carboxylate Deaminase (AAC-Deaminase). They can also be used as bio-fertilizers or as biocontrol agents, by producing antibiotics, exo-polysaccharides, or hydrolytic enzymes. In this review, the connections between microbial populations, as microbial inoculants, and plant systems are highlighted, focusing on the enhancement of plant development, environmental resilience of agricultural systems, ecosystem services, and biological challenges under stressed conditions. This review also emphasizes the use of advanced molecular tools and techniques to effectively characterize potent soil microbial communities, their importance in increasing crop yield in stressed soils, and the prospects for future research.
... By evaluating the results of Mann-Kendall test given in Table 3, it is obvious that the trend is positive for the used data of this study, which presents an increasing trend. In scientific literature, droughts are commonly classified into four main categories: meteorological, hydrological, agricultural, and socio-economic (Wilhite & Glantz, 1985;Mishra & Singh, 2010;Tallaksen & Lanen, 2004). For this particular study, meteorological drought was the focus, with an emphasis on analyzing drought using rainfall data. ...
Drought is one of the most important challenges that many countries, especially countries in the Middle East region, are struggling with. Based on this, the study and monitoring of hydrological and drought factors is an important issue that can have a significant impact on management decisions in the field of water resources, especially in crisis management. Therefore, investigating the drought parameters is very important to understand the drought situation of a region. In this study, Alanya region, which is located on the southern coast of Turkey, was selected as a case study for drought analysis. Four drought indices for the selected region including: China Z-Index (CZI), Standardized Precipitation Index (SPI), Modified China Z-Index (MCZI) and Z-Score Index (ZSI) have been investigated. All these indicators have been investigated and evaluated using time scales of 1, 6, 12 and 24 months, the coefficient of determination (R2) has been calculated for each drought index with a different time scale and their results have been compared. The findings of the research showed that SPI and CZI drought indices performed better than other selected drought indices in identifying and effectively tracking drought severity. In addition to the study of dry events, wet events were also investigated, which indicates the presence of consecutive floods in the last years of the studied period in the region. The results indicated similar very dry events for the selected indicators in the 6-month period. Also, the rainfall trend for the period of 2015-2022 was taken into consideration to examine the rainfall of the last eight years. The results show that precipitation has decreased in recent years and has a downward trend in most months of the period in question, and the possibility of flood events due to sudden showers in the region has increased due to the continuation of droughts experienced in the years before 2015. Investigating soil moisture and vegetation for the selected period in the study area is also important for the evaluation of the drought level. Evaluation of the available land (vegetation) cover maps of the years 1975, 1985, 2000, 2010, 2020 and 2022 show that the vegetation cover has weakened over the years, and it has been evaluated as an indicator that the danger of drought in the region has increased.
... type (Mishra et al. 2010; Wilhite and Glantz 1985). Meteorological drought which often affects water resources and 37 available water availability is one of the most difficult to predict and detect. ...
Defined as a decrease in average rainfall amounts, drought is one of the most insidious natural disasters. When it starts, people may not be aware of it, that's why droughts are difficult to monitor. Scientists have long been working to predict and monitor droughts. For this purpose, they have developed many methods such as drought indices one of which Standardized Precipitation Index (SPI) is. In this study, SPI to detect droughts and machine learning algorithms, support vector machines (SVM), artificial neural networks (ANN), random forest (RF), decision tree (DT), frequently used in the literature to predict droughts and 3 different statistical methods: correlation coefficient (r), Root Mean-square Error (RMSE), Nash-Sutcliffe Efficiency (NSE) Coefficient to investigate model performance values were used. Wavelet analysis was also applied to improve model performances. Konya closed basin located in the middle of Türkiye in terms of location and is among the leading regions of Turkey in terms of grain is one of the regions most affected by droughts in Türkiye. One of the most important water resources of the region is the Apa dam. It provides water to many fields which fertile land in its vicinity and is affected by droughts. Therefore, this region was determined as the study area. Meteorological data, total monthly precipitation, that could represent the region were obtained between 1955 and 2020 from general directorate of state water works and general directorate of meteorology. The results show that among the models analyzed with machine learning algorithms, the best results were obtained from M04 model whose input structure was created from SPI, different times steps, data delayed up to 5 months and total monthly precipitation data for time t-1. Among machine learning algorithms, SVM has achieved the most successful results in not only without wavelet transform (WT) but also with WT. Effective results were obtained from M04 in which SVM with WT was used (NSE = 0.9942, RMSE = 0.0764, R = 0.9971).
Drought is associated with adverse environmental and societal impacts across various regions. Therefore, drought monitoring based on a single variable may lead to unreliable information, especially about the onset and persistence of drought. Previous studies show vapor pressure deficit (VPD) data can detect drought onset earlier than other drought indicators such as precipitation. On the other hand, soil moisture (SM) is a robust indicator for assessing drought persistence. This study introduces a nonparametric multivariate drought index Vapor Pressure Deficit Soil moisture standardized Drought Index (VPDSDI) which is developed by combining VPD with SM information. The performance of the multivariate index in terms of drought onset detection is compared with the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) for six major drought events across the United States including three rapidly developing drought events (this term refers to flash droughts that develop on monthly scales) and three conventional drought events. Additionally, the performance of the proposed index in detecting drought persistence is compared with the Standardized Soil moisture Index (SSI), which is an agricultural drought index. Results indicate the multivariate index detects drought onset always earlier than SPI for conventional events, but VPDSDI detects drought onset earlier than or about the same time as SPEI for rapidly developing droughts. In terms of persistence, VPDSDI detects persistence almost identical to SSI for both rapidly developing and conventional drought events. The results also show that combining VPD with SM reduces the high variability of VPD and produces a smoother index which improves the onset and persistence detection of drought events leveraging VPD and SM information.
Drought stress is an issue of great concern for various regions of the world. As climate change continues to impact our planet, drought stress is becoming increasingly prevalent, causing severe consequences for ecosystems, agriculture, and human livelihoods. Drought stress can lead to reduced crop yields, soil erosion, and desertification, among other environmental problems. In addition, it can have a significant impact on human health, with dehydration and malnutrition being common issues in areas affected by drought. One of the most significant challenges associated with drought stress is its complexity. Drought stress is multifaceted, with numerous factors contributing to its development and impact. To address this challenge effectively, a holistic approach is required. This approach involves understanding the complexities of drought stress and developing sustainable solutions to mitigate its impact. By examining the underlying mechanisms of drought stress, we can identify the various factors that contribute to its development and severity. Once we have a deeper understanding of the underlying mechanisms of drought stress, we can develop effective management strategies to mitigate its adverse effects. These strategies can include measures such as water conservation, soil management, and the use of drought-resistant crops. Additionally, we can explore innovative approaches such as drought forecasting and early warning systems to help communities and governments prepare for and mitigate the impact of drought stress.
Streamflow flash droughts (SFDs) occur due to a rapid decline in streamflow and cause major challenges associated with water availability for downstream ecosystems, hydropower generation, and irrigation water demand. Human interventions such as reservoir operations and reservoir storage can considerably influence streamflow variability. However, the crucial role of dams/reservoirs on the occurrence of SFDs in India remains unexamined. Using a combination of hydrological and hydrodynamical models, we examined the role of reservoirs on SFDs in India during 1971–2020. Reservoirs play a considerable role in the occurrence of SFDs during the summer monsoon season (June‐September) in India. The frequency and severity of SFDs in the presence of reservoirs are substantially lesser than in the absence of them. In addition, high and low antecedent reservoir storage conditions before meteorological flash droughts (MFDs) do not support the rapid decline of streamflow (i.e., SFDs) downstream of reservoirs, while the medium reservoir storage conditions prior to MFDs favor the development of SFDs. Similar to conventional (or long‐term) streamflow droughts (SDs), SFDs are more frequent in the El Nino phase than in the La Nina phase. Unlike the long‐term streamflow droughts, the implementation of dams considerably reduces the frequency of SFDs during both the negative and positive phases of El Nino Southern Oscillation. Overall, our findings demonstrate the considerable role of human interventions in flash drought occurrence, as SFDs are triggered by MFDs but modulated by reservoir storage and operations.
In this work we analyse yearly standardized precipitation evapotranspiration index for accumulation timescale of 6 months (SPEI‐6) for August which has been identified as a strong proxy for corn production in Serbia. By applying recently proposed method generalized weighted permutation entropy (GWPE), which provides the information about predictability of large/small fluctuations in nonstationary time series, on SPEI index calculated from high‐resolution gridded dataset for the period 1951–2022, we found that the small fluctuation sequences of consecutive 4‐year SPEI values are the most predictable (indicated by lowest entropy values). The order of large fluctuation sequences is less predictable, while the order of sequences considering all magnitudes of fluctuations are the least predictable (indicated by highest entropy values). We also analysed 4‐month SPEI‐6 sequences for May, June, July and August (during the growing season of corn) along the years under study and found that they display lower GWPE values and thus are more predictable than yearly SPEI‐6 August sequences (small fluctuations displaying lower entropy values than large fluctuations). Regarding spatial distributions, in both cases SPEI‐6 sequences show similar pattern for large fluctuations: higher predictability (lower entropy values) in northern and eastern part of Serbia and lower predictability (higher entropy values) in southern and western part. For small fluctuations spatial distribution of GWPE values indicates that yearly SPEI‐6 August series are more predictable in the western part of the country while May to August monthly SPEI‐6 sequences are more predictable in the eastern part.
Evaluating drought parameters at the basin level is one of the fundamental processes for planning sustainable crop production. This study aimed to evaluate both short-term and long-term meteorological drought parameters within the Vaippar Basin, located in southern India, by employing the standardized precipitation index (SPI). Gridded rainfall values developed from 13 rain gauge stations were employed to calculate the SPI values. Drought parameters, encompassing occurrence, intensity, duration, frequency, and trends, were assessed for both short-term and long-term droughts. The study findings indicated that the occurrence of short-term drought was 51.7%, while that of long-term drought was 49.82%. Notably, the basin experienced extreme short-term droughts in 1980, 1998 and 2016 and long-term droughts in 1981, 2013, and 2017. Utilizing an innovative trend identification method for SPI values, a significant monotonic upwards trend was identified in October and December for short-term drought and in December for long-term drought. This study defined the minimum threshold rainfall, which represents the critical amount required to prevent short-term drought (set at 390 mm) and long-term drought (set at 635 mm). The drought severity recurrence curves developed in this study indicate that when the SPI values fall below − 1.0, short-term drought affects 25% of the basin area, while long-term drought impacts 50% of the basin area at a 20-year recurrence interval. Additionally, the drought hazard index (DHI), which combines drought intensity and severity, demonstrated higher values in the northwestern regions for short-term drought and in the southern areas for long-term drought. The study's findings, highlighting areas of drought vulnerability, severity, and recurrence patterns in the basin, direct the attention for timely intervention when drought initiates.
Global drylands, covering over 40% of Earth's land surface, are important among worldwide ecoregions and support large human and livestock populations. However, these ecologically sensitive ecoregions are undergoing a rapid transformation resulting from climate change, socioeconomic and political factors, increases in population, and ever-growing demands for goods and services. Managing Soil Drought addresses basic processes and provides specific case studies throughout covering the protection, restoration, and sustainable management goals of global drylands under changing and harsh climatic conditions, including fragile and vulnerable ecosystems. The book is written by numerous researchers, academicians, practitioners, advocates, land managers, and policymakers involved in bringing about transformation in these regions important to human and nature. It includes information on basic strategies for sustainable management of global drylands aimed at improving water use efficiency through choosing appropriate species, developing new varieties, using organic and inorganic amendments, and scaling up innovative farming systems. This volume in the Advances in Soil Sciences series is an essential read for development organizations and policymakers involved in improving crop productivity and sustainability in drought-prone regions; students, researchers, and academicians interested in sustainable management of water resources; and those involved in emerging concepts of regenerative agriculture, agroecology, and conservation agriculture.
The objective of the authors is examines drought trends in Sicily over the past century. The analysis focuses on the nine provinces that comprise the region, The Standardized Precipitation Index (SPI) is used to identify pluviometric deficit at different time scales, including 3, 6, 12, and 24 months. Additionally, the Mann-Kendall test is applied to check if the SPI has a significant trend, especially if it is decreasing; as the SPI decreases, the pluviometric deficit increases.The statistical approach of the study confirms that in Sicily, meteorological and hydrological droughts are becoming more frequent. In addition, a rising trend of socio-economic droughts has been identified. It is therefore necessary to target mitigation and adaptation measures on the areas most vulnerable to drought in order to safeguard the agricultural sector and, consequently, a significant part of the region's productive activities. The methods used in this work could be applied to the management of water resources and the protection of the island's agricultural and economic sectors.
Resistance and resilience are widely used to characterize ecosystem drought stability. Tradeoff between resistance and resilience have been reported, but its long‐term trends remain uncertain at global scale. Based on remotely sensed vegetation indices, we assessed the spatiotemporal dynamics of drought resistance and resilience. Result revealed that there was a significant decline in the tradeoff between resistance and resilience, corresponding to a substantial increase in the proportion of areas with high resistance‐high resilience or low resistance‐low resilience. In the South Sahel, South Africa and Central China, the increased precipitation and vegetation coverage contribute to enhanced drought stability constructed by resistance and resilience; while rising temperature, decreased water availability and deforestation lead to declined stability in northeastern North America, South America and the Congo region. Increases in the areas with low resistance‐low resilience resulting from declining tradeoffs warn of increased regional ecosystem vulnerability.
One of the most common natural hazards that can endanger life and property is drought, which can happen under a variety of weather and environmental circumstances. This study aims to monitor the agricultural and metrological drought in the Wasit Province using remote sensing data. Landsat 8 images were used to create the agriculture drought maps based on the NDVI for the years 2013, and 2023. Additionally, SPI-12 was used for the same years to evaluate the meteorological drought. The findings demonstrated that while SPI readings in 2023 were lower, the SPI-12 in 2013 indicated near-normal drought types. Two types of drought have been identified: moderate and slight. The result shows that, for the year 2013 the percentage of moderate drought is 31%, slight drought 64%, and no drought 3.9% from the total area. While, in 2023 the percentage of moderate drought is 47%, slight drought 49%, and no drought 3.2% from the total area. It is noticed that in 2023, the moderate drought class increased by about 16%. Government planners may find this results valuable when developing and managing drought consequences.
As known, Algeria is a dry country that belongs to the arid-semi-arid climate (Smadhi et al., 2022). These vast interior spaces are characterized by a dry and cold climate in winter, and hot and dry in summer (Bachir et al., 2022). A deficient and irregularly distributed rainfall characterizes the climatic conditions that exert a very strong influence on agricultural growth (Bachir et al., 2016). They are an obstacle to the adoption of intensive agricultural practices without irrigation (Bachir et al., 2021). A judicious use of water in the main sectors of agriculture, industry and drinking water supply, should be based on the knowledge of its hydrochemical status (Hosseinifard and Mirzaei, 2015). The latter is a function of the mineralization acquisition process and pollution (Sayeh et al., 2022). Many factors are involved in the chemistry of water, such as climate, geology, the presence of a sea, and human action (Peters and Maybeck, 2000). Thus, it is prudent to link the changes in the chemical character of waters to natural conditions and anthropogenic activities. Due to their location on the surface, surface waters are relatively less loaded with minerals than ground waters, which are subject to geochemical, natural processes resulting from water-rock interactions. Numerous research studies have elucidated these geochemical reactions through case studies (Gupta et al., 2008; Al-Ahmadi and El-Fiky, 2009; Senthilkumar and Elango, 2013; Barbieri et al., 2017; Yi et al., 2017). Several approaches were used to assess water geochemistry. By using the determination of chemical facies or factors approach, it is possible to identify, the mixing processes of waters (Selvakumar et al., 2017), the recharge zones (Dragon and Gorski, 2015) or the chemical evolution of waters due to the human activities which impact in a direct or indirect way in the modification of hydrochemical behaviour (Eloïse, 2017). Geochemical indicators are widely discussed in the literature and have used the following parameters: Saturation and Chloro-alkalines indices, Gibbs diagram and some characteristic ion ratios. Human, through diverse activities, participates in a direct or indirect way in the modification of hydrochemical behavior.
Algeria, as well as developing countries, has reoriented the concept of food security through institutional and administrative measures and policies aimed at improving the access of populations to abundant and healthy food. Thus, it is the availability of food, the accessibility to this food, the proper use, and the stability and safety of supplies (Amrani, 2021). Ambitious public policies put in place in terms of irrigation, energy and infrastructure development, also associated with the emergence of local economic dynamics, have allowed an extraordinary development of agriculture, especially in the Saharan regions, thus aiming to modernize agriculture with the purpose of increasing and stabilizing agricultural and food production (Bencharif, 2018). Benefiting from these incentives, in favor of Saharan agricultural projects, the increasing aggregation of the population in urban centers and, subsequently, the growth of consumer markets, stimulate the economic development of the entire region (Kouzmine et al., 2009).
La sequía, la aridez y las olas de calor son fenómenos intensificados por el calentamiento de la troposfera, exacerbado por actividades humanas que incrementan los gases de efecto invernadero. Paralelamente, la estratosfera se está enfriando, lo que afecta los patrones climáticos globales y contribuye a eventos climáticos extremos. Estos cambios tienen profundas implicaciones en los ecosistemas, especialmente en los bienes hídricos, la producción de alimentos y la salud humana, obligando a pensar en alternativas sostenibles y adaptativas en la agricultura y la gestión de los bienes naturales.
La ciencia desempeña un rol elemental en la gestión de estos desafíos climáticos, ofreciendo datos y modelos para la toma de decisiones informada y la implementación de estrategias de mitigación. Es esencial la adopción de tecnologías ambientalmente sostenibles y la colaboración internacional para limitar el calentamiento global y sus efectos, así como darle verdadera aplicación al Acuerdo de París. Con estas acciones, se debe proteger y preservar el clima de la Tierra a largo plazo, asegurando la resiliencia y el bienestar de las generaciones futuras de todos los continentes.
The changing climate makes it more difficult to manage water resources and food production sustainably. Various adaptation measures have been proposed to moderate the negative impacts of climate change; however, implementation of these measures may be hampered by other factors even if the benefits are acknowledged—a situation termed “soft adaptation limits” by the IPCC. We hypothesized that societal rules can be a potential barrier to adaptive action if they are too fixed, because such rules have coevolved with the interactions between the past climate and human activities. To test this hypothesis, we present a framework based on the assumption that associated societal rules of Japan's matured irrigation systems are potential barriers to adaptation. The framework consisted of two process‐based models, one to evaluate the water deficit risk and one to evaluate the benefits of optimizing rice yield and quality. We applied each model to an experiment in which we shifted the current transplantation date by 1 week for up to 5 weeks before and after the current date under the historical (1981–2000) and RCP 2.6 and 8.5 (2011–2030 and 2031–2050) scenarios. We revealed two contrasting development pathways in the study watershed. Soft adaptation limits imposed by water availability will occur by 2030 if farmers optimize for quality, whereas mutual benefits to farmers and river administrators will be achieved if farmers seek yield. We argue that more participatory research with stakeholder engagement, as well as policy discussions about these possible developments, is needed to ensure successful adaptation.
A cascade of drought impacts refers to a series of interconnected events that trigger a chain reaction of impacts, extending beyond water scarcity, to affect agricultural production, socio-economic factors, and the environment. This paper aims to understand the role of society in mitigating drought impacts, particularly through policy responses. Conducting a case study in Ceará state, northeast Brazil, we used a global rare dataset of continuously drought monitoring, complemented by interviews with smallholder farmers and agricultural extension technicians. Additionally, we analyzed policy documents related to public policies implemented at the local level. Employing a classification of drought impacts as our analytical framework, our findings indicate that socio-environmental-economic impacts of drought are less frequently reported, suggesting that development policies are mitigating cascading effects on livelihoods. Most impacts are associated with hydrological impacts of drought, suggesting unintended consequences of investments in increasing water supply. We emphasize the significant contribution of public policies to mitigating the cascading effects of drought, which do not necessarily involve increasing water availability, but strengthen the local economy.
Developing an effective and reliable integrated drought index is crucial for tracking and identifying droughts. The study employs game theory to create a spatially variable weight drought index (GTDI) by combining two single-type indices: the agricultural drought index (SSMI), which implies drought hazard-bearing conditions, and the meteorological drought index (SPEI), which implies drought hazard-causing conditions. Also, the entropy theory-based drought index (ETDI) is induced to incorporate a spatial comparison to the GTDI to illustrate the rationality of gaming weight integration. Leaf Area Index (LAI) data is employed to confirm the reliability of the GTDI in identifying drought by comparing it with the SPEI, SSMI, and ETDI. Furthermore, an assessment is conducted on the temporal trajectories and spatial evolution of the GTDI-identified drought to discuss the GTDI’s advancedness in monitoring changes in hazard-causing and bearing impacts. The results showed that the GTDI has a greatly high correlation with single-type drought indices (SPEI and SSMI), and its gaming weight integration is more logical and trustworthy than the ETDI. As a result, it outperforms ETDI, SPEI, and SSMI in recognizing drought spatiotemporally, and is projected to replace single-type drought indices to provide a more accurate picture of actual drought. Additionally, GTDI exhibits the gaming feature, indicating a distinct benefit in monitoring changes in hazard-causing and bearing impacts. The case studies show drought events in the Wei River Basin are dominated by a lack of precipitation. The hazard-causing index SPEI dominates the early stages of a drought event, whereas the hazard-bearing index SSMI dominates the later stages. This study surely serves as a helpful reference for the development of integrated drought indices as well as regional drought mitigation, prevention, and monitoring.
This study aims to quantify meteorological–hydrological drought propagations and examine the potential impacts by climatic variability, LULC change (LULC), and human regulations. An integrated observation-modeling framework quantifies drought propagation intervals and assesses mechanisms influencing hydrological droughts. Meteorological droughts are characterized using the Standardized Precipitation Evapotranspiration Index (SPEI), and hydrological droughts are assessed through the Standardized Streamflow Index (SSI) across diverse climatic zones. Cross-correlation analysis between SPEI and SSI time series identifies the lag time associated with the highest correlation as the drought propagation interval. Mechanisms are investigated via a coupled empirical-process modeling framework incorporating the Soil and Water Assessment Tool (SWAT). Discrepancies between simulated and observed SSI time series help quantify the extent of human regulation impacts on hydrological drought characteristics and propagation. The Yellow River Basin (YRB), divided into six subzones based on climate characteristics, is selected as the case study. Key findings include: (1) Meteorological droughts were extremely severe across most YRB during the 1990s, while the 2000s showed some mitigation primarily due to precipitation increases. (2) Hydrological droughts and propagation times from meteorology to hydrology demonstrated substantial spatiotemporal variability. In general, summer propagation times were shorter than other seasons. (3) Propagation times were shorter in arid regions with cropland or built-up land cover versus grassland and woodland, while the reverse held for humid regions. (4) Human regulations prolonged propagation times, likely due to reservoir regulations designed to overcome water deficits. While the YRB is the focus of this paper, the methodologies and findings are applicable to other regions worldwide to enhance drought forecasting and water resource management. In various hydrological and climatic contexts worldwide.
In undammed watersheds in Mediterranean climates, the timing and abruptness of the transition from the dry season to the wet season have major implications for aquatic ecosystems. Of particular concern in many coastal areas is whether this transition can provide sufficient flows at the right time to allow passage for spawning anadromous fish, which is determined by dry season baseflow rates and the timing of the onset of the rainy season. In (semi-) ephemeral watershed systems, these functional flows also dictate the timing of full reconnection of the stream system. In this study, we propose methods to predict, approximately 5 months in advance, two key hydrologic metrics in the undammed rural Scott River watershed in northern California. The two metrics are intended to characterize (1) the severity of a dry year and (2) the relative timing of the transition from the dry to the wet season. The ability to predict these metrics in advance could support seasonal adaptive management. The first metric is the minimum 30 d dry season baseflow volume, Vmin, which occurs at the end of the dry season (September–October) in this Mediterranean climate. The second metric is the cumulative precipitation, starting 1 September, necessary to bring the watershed to a “full” or “spilling” condition (i.e., initiate the onset of wet season storm- or baseflows) after the end of the dry season, referred to here as Pspill. As potential predictors of these two metrics, we assess maximum snowpack, cumulative precipitation, the timing of the snowpack and precipitation, spring groundwater levels, spring river flows, reference evapotranspiration, and a subset of these metrics from the previous water year. Though many of these predictors are correlated with the two metrics of interest, we find that the best prediction for both metrics is a linear combination of the maximum snowpack water content and total October–April precipitation. These two linear models could reproduce historical values of Vmin and Pspill with an average model error (RMSE) of 1.4 Mm3 per 30 d (19.4 cfs) and 25.4 mm (1 in.), corresponding to 49 % and 37 % of mean observed values, respectively. Although these predictive indices could be used by governance entities to support local water management, careful consideration of baseline conditions used as a basis for prediction is necessary.
Streamflow flash droughts (SFDs), characterized by a rapid decline in streamflow over a relatively short period, affect water availability, hydropower generation, and the ecosystem. However, atmospheric and land processes that drive SFDs in the monsoonal climate of India remain unexplored. Using observations, reanalysis data sets, and model simulations, we examined the critical drivers of SFDs in 64 catchments in India during the 1971–2018 period. We identified meteorological flash droughts (MFDs) using precipitation and SFDs using in situ observations and model simulations of streamflow. We show that precipitation deficit and anomalous high temperature, driven mainly by the summer monsoon breaks, lead to the development of MFDs. Antecedent baseflow conditions play a major role in the propagation of MFDs to SFDs. Favorable atmospheric conditions (driven by the monsoon breaks) cause MFDs, which translate to SFDs. High and low baseflow conditions limit the rapid decline in streamflow, which controls the occurrence of streamflow flash drought. On the other hand, favorable atmospheric conditions combined with moderate baseflow can trigger SFDs in India during the summer monsoon season. Moreover, humid catchments are more prone to propagation from MFDs to SFDs during the monsoon season in India. Understanding the crucial role of atmospheric and land drivers can assist in examining the occurrence of streamflow flash drought with implications for water resources planning and management.
Drought, defined as the period when water availability considerably remains below normal levels for a certain time period, has devastating social, economic and environmental impacts. It is significant to closely monitor the temporal and spatial variability of drought in order to implement policies to mitigate the drought risk and ensure the sustainable management of water resources. In this study, three different drought indices, standard precipitation index (SPI), standardized precipitation‐evapotranspiration index (SPEI) and reconnaissance drought index (RDI), are calculated for 3‐, 6‐ and 12‐month time scales from the precipitation and temperature data measured in 11 meteorological observation stations within the Mediterranean coastal region of Türkiye during 1972–2020. Initially, two absolute homogeneity tests were applied, namely the standard normal homogeneity test (SNHT) and the Pettitt test, to detect abrupt changes in drought index time series. Then, trend analysis was carried out with the innovative trend analysis (ITA) and improved visualization of ITA (IV‐ITA) methods to determine the temporal variation of the drought in the region. A graphical representation is developed for the drought classifications based on IV‐ITA. As a result of the SNHT and Pettitt test, significant change points were found at a 5% significance level in 91.92% and 85.86% of all indices, respectively. In both tests, breaks were detected at similar times (between 1972 and 1974) at Marmaris station, while at Alanya station, changes were found between 1972 and 1973 for the SNHT and in 2008 for the Pettitt test. The trend differences between extreme conditions (extremely dry and wet) decreased with an increase in time scale, distinctively. The ITA trends were almost identical for 3‐month time scales, and they started to differ with time scale increases. Particularly, the presence of negative differences in data points contributes to the augmentation of drought periods, despite a few instances of extreme cases and minor fluctuations that can also be observed in IV‐ITA. The findings obtained from the study are expected to provide valuable information about the recent shifts in drought in the Mediterranean basin.
Michael H. Glantz and Richard W. Katz, of the Environmental and Societal Impacts Group at the National Center for Atmospheric Research, Boulder, Colorado, draw on the case of the Sahel to comment on the use of the term `drought' for arid regions
Droughts and floods, as precipitation excesses, are quite different natural hazards, and each costs the United States more than $1 billion in losses annually. At the impact and policy levels, confusion arises from an inability to define droughts suitably and to identify flood losses in a quantitative way, unaffected by population changes, land use shifts, and other socioeconomic factors. Examples from Illinois research are used to show how relationships can be developed between generally understandable precipitation values and drought or flood losses in various economic sectors and land use areas. Then, the time and space variations of the events can be objectively assessed by using the precipitation data, providing meaningful scientific-engineering definitions for use by decision makers.