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Relations between rainfall and the altitude of the terrain can have significant implications for rainfall-runoff studies in hydrology. The aim of this paper is to report on a study of relationships between annual and seasonal rainfall and the altitude of the terrain in Saudi Arabia (SA) using global ordinary least square (OLS) and local geographica...
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... This vast region spans approximately 2,150,000 square kilometers, constituting approximately 80% of the Arabian Peninsula's land [66][67][68]. KSA has approximately 2800 km of coastline along the Red Sea and the Arabian Gulf, with both bodies of water serving as the main suppliers of water vapor for the country [69]. The Kingdom of Saudi Arabia is characterized by noticeable topographical diversity. ...
Arid regions are susceptible to flash floods and severe drought periods, therefore there is a need for accurate and gap-free rainfall data for the design of flood mitigation measures and water resource management. Nevertheless, arid regions may suffer from a shortage of precipitation gauge data, whether due to improper gauge coverage or gaps in the recorded data. Several alternatives are available to compensate for deficiencies in terrestrial rain gauge records, such as satellite data or utilizing geostatistical interpolation. However, adequate assessment of these alternatives is mandatory to avoid the dramatic effect of using improper data in the design of flood protection works and water resource management. The current study covers 75% of the Kingdom of Saudi Arabia’s area and spans the period from 1967 to 2014. Seven satellite precipitation datasets with daily, 3-h, and 30-min temporal resolutions, along with 43 geostatistical interpolation techniques, are evaluated as supplementary data to address the gaps in terrestrial gauge records. The Normalized Root Mean Square Error by the mean value of observation (NRMSE) is selected as a ranking criterion for the evaluated datasets. The geostatistical techniques outperformed the satellite datasets with 0.69 and 0.8 NRMSE for the maximum and total annual records, respectively. The best performance was found in the areas with the highest gauge density. PERSIANN-CDR and GPM IMERG V7 satellite datasets performed better than other satellite datasets, with 0.8 and 0.82 NRMSE for the maximum and total annual records, respectively. The spatial distributions of maximum and total annual precipitation for every year from 1967 to 2014 are generated using geostatistical techniques. Eight Probability Density Functions (PDFs) belonging to the Gamma, Normal, and Extreme Value families are assessed to fit the gap-filled datasets. The PDFs are ranked according to the Chi-square test results and Akaike information criterion (AIC). The Gamma, Extreme Value, and Normal distribution families had the best fitting over 56%, 34%, and 10% of the study area gridded data, respectively. Finally, the selected PDF at each grid point is utilized to generate the maximum annual precipitation for 2, 5, 10, 25, 50, and 100-year rasters that can be used directly as a gridded precipitation input for hydrological studies.
... However, most were mainly based on the mean precipitation (averaged over the entire study area). It is noteworthy that orographic factors greatly influence the spatial variability of rainfall over complex topographies (e.g., areas near mountains) by initiating and enhancing rainfall (Basist et al., 1994;Goovaerts, 2000;Al-Ahmadi and Al-Ahmadi, 2013;Zhang et al., 2017;Yu et al., 2018;Sarmadi et al., 2019). Previous studies have revealed that the mean and maximum rainfall of station observations increase, reach a maximum, and then decrease as the elevation becomes higher (Fo, 1992;Bookhagen and Burbank, 2006;Nikolopoulos et al., 2015;Salerno et al., 2015;Zhou et al., 2019). ...
Based on hourly rain gauge data during May–September of 2016–20, we analyze the spatiotemporal distributions of total rainfall (TR) and short-duration heavy rainfall (SDHR; hourly rainfall ⩾ 20 mm) and their diurnal variations over the middle reaches of the Yangtze River basin. For all three types of terrain (i.e., mountain, foothill, and plain), the amount of TR and SDHR both maximize in June/July, and the contribution of SDHR to TR (CST) peaks in August (amount: 23%; frequency: 1.74%). Foothill rainfall is characterized by a high TR amount and a high CST (in amount); mountain rainfall is characterized by a high TR frequency but a small CST (in amount); and plain rainfall shows a low TR amount and frequency, but a high CST (in amount). Overall, stations with high TR (amount and frequency) are mainly located over the mountains and in the foothills, while those with high SDHR (amount and frequency) are mainly concentrated in the foothills and plains close to mountainous areas. For all three types of terrain, the diurnal variations of both TR and SDHR exhibit a double peak (weak early morning and strong late afternoon) and a phase shift from the early-morning peak to the late-afternoon peak from May to August. Around the late-afternoon peak, the amount of TR and SDHR in the foothills is larger than over the mountains and plains. The TR intensity in the foothills increases significantly from midnight to afternoon, suggesting that thermal instability may play an important role in this process.
... According to the Köppen climate classification system [35,36], the majority of Saudi Arabia is a hot and arid desert; however, the southwest region of Saudi is considered semi-arid [37,38]. Precipitation is scant and infrequent in most regions of Saudi Arabia, with the wet season occurring from October to April [37,39]. During dry months, hardly any precipitation occurs, with the exception of the southwest area of the country [39,40]. ...
... Precipitation is scant and infrequent in most regions of Saudi Arabia, with the wet season occurring from October to April [37,39]. During dry months, hardly any precipitation occurs, with the exception of the southwest area of the country [39,40]. ...
... The lower CC values during moderate rainfall events could be linked to the orographic effects of the prominent mountainous region in Saudi Arabia [27,44]. In arid regions like Saudi Arabia, the interaction between topography and precipitation is a crucial factor influencing the spatial distribution of rainfall [39]. Mountains can act as barriers to moist air masses, leading to orographic lifting on the windward side and subsequently enhancing rainfall in those areas. ...
In the past decade, Saudi Arabia has witnessed a surge in flash floods, resulting in significant losses of lives and property. This raises a need for accurate near-real-time precipitation estimates. Satellite products offer precipitation data with high spatial and temporal resolutions. Among these, the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks–Dynamic Infrared Rain Rate near-real-time (PDIR-Now) stands out as a novel, global, and long-term resource. In this study, a rigorous comparative analysis was conducted from 2017 to 2022, contrasting PDIR-Now with rain gauge data. This analysis employs six metrics to assess the accuracy of PDIR-Now across various daily rainfall rates and four yearly extreme precipitation indices. The findings reveal that PDIR-Now slightly underestimates light precipitation but significantly underestimates heavy precipitation. Challenges arise in regions characterized by orographic rainfall patterns in the southwestern area of Saudi Arabia, emphasizing the importance of spatial resolution and topographical considerations. While PDIR-Now successfully captures annual maximum 1-day and 5-day precipitation measurements across rain gauge locations, it exhibits limitations in the length of wet and dry spells. This research highlights the potential of PDIR-Now as a valuable tool for precipitation estimation, offering valuable insights for hydrological, climatological, and water resource management studies.
... The KSA overlooks both the Arabian Gulf and the Red Sea, boasting 550 and 2250 km of shoreline, respectively. These water bodies serve as the kingdom's primary sources of water vapor [55]. The KSA has a complex topography that can be classified into four categories: (1) coastal plains, (2) central and northern plateaus, (3) the central Tuwayq mountains, and (4) the western Asir mountains. ...
Providing an accurate spatiotemporal distribution of rainfall and filling data gaps are pivotal for effective water resource management. This study focuses on the Asir region in the southwest of Saudi Arabia. Given the limited accuracy of satellite data in this arid/mountain-dominated study area, geospatial interpolation has emerged as a viable alternative approach for filling terrestrial records data gaps. Furthermore, the irregularity in rain gauge data and the yearly spatial variation in data gaps hinder the creation of a coherent distribution pattern. To address this, the Centered Root Mean Square Error (CRMSE) is employed as a criterion to select the most appropriate geospatial interpolation technique among 51 evaluated methods for maximum and total yearly precipitation data. This study produced gap-free maps of total and maximum yearly precipitation from 1966 to 2013. Beyond 2013, it is recommended to utilize ordinary Kriging with a J-Bessel semivariogram and simple Kriging with a K-Bessel semivariogram to estimate the spatial distribution of maximum and total yearly rainfall depth, respectively. Additionally, a proposed methodology for allocating additional rain gauges to improve the accuracy of rainfall spatial distribution is introduced based on a cross-validation error (CVE) assessment. Newly proposed gauges in the study area resulted in a significant 21% CVE reduction.
... KSA has a western 2250 km shoreline along the Red Sea and an eastern one of 550 km along the Arabian Gulf. The two water bodies are the source of water vapor in the country [60]. KSA's main topographic features is classified into coastal plains, northern and Najd plateaus, the Empty Quarter Desert, the Tuwayq mountains, and Asir Mountains. ...
Rainfall depth is a crucial parameter in water resources and hydrological studies. Rain gauges provide the most reliable point-based rainfall estimates. However, they do not have a proper density/distribution to provide sufficient rainfall measurements in many areas, especially in arid regions. To evaluate the adequacy of satellite datasets as an alternative to the rain gauges, the Kingdom of Saudi Arabia (KSA) is selected for the current study as a representative of the arid regions. KSA occupies most of the Arabian Peninsula and is characterized by high variability in topographic and climatic conditions. Five satellite precipitation datasets (SPDSs)-CMORPH, PERSIANN-CDR, CHIRPS V2.0, TMPA 3B42 V7, and GPM IMERG V6-are evaluated versus 324 conventional rain-gauges' daily precipitation measures. The evaluation is conducted based on nine quantitative and categorical metrics. The evaluation analysis is carried out for daily, monthly, yearly, and maximum yearly records. The daily analysis revealed a low correlation for all SPDSs (<0.31), slightly improved in the yearly and maximum yearly analysis and reached its highest value (0.58) in the monthly analysis. The GPM IMERG V6 and PERSIANN-CDR have the highest probability of detection (0.55) but with a high false alarm ratio (>0.8). Accordingly, in arid regions, the use of daily SPDSs in rainfall estimation will lead to high uncertainty in the obtained results. The best performance for all statistical metrics was found at 500-750 m altitudes in the central and northern parts of the study area for all satellites except minor anomalies. CMORPH dataset has the lowest centered root mean square error (RMSEc) for all analysis periods with the best results in the monthly analyses.
... O modelo GWR produz informações que explicam a variação espacial a partir das associações entre variáveis. A hipótese é que as características adjacentes têm um efeito maior nas estimativas dos parâmetros que as características mais distantes espacialmente (AL-AHMADI; AL-AHMADI, 2013;MENNIS, 2006). Para especificar a estrutura de ponderação geográfica o modelo GWR requer a especificação de uma forma de kernel e uma largura de banda. ...
... Valores de r² mais elevados indicam maior capacidade do modelo de explicar mais variações da variável dependente como função das variáveis independentes. O AICc é um indicador da precisão e da complexidade do modelo, as diminuições no valor do AICc indicam que o modelo está mais próximo da realidade (AL-AHMADI; AL-AHMADI, 2013;BROWN et al., 2012;CHARLTON, 2002;MENNIS, 2006 ...
A ilha de calor urbana de superfície (ICUS) é o fenômeno urbano mais evidente das transformações provocadas pela ação humana, e, por conseguinte, das alterações climáticas em escala local. Diante disso, essa pesquisa teve como objetivo modelar a ICUS por meio de modelos estacionários (MQO) e não estacionários (GWR) utilizando variáveis naturais e antrópicas (Altitude, Índice de Posição Topográfica - IPT, Normalized Difference Vegetation Index - NDVI, Índice da Diferença Normalizada de Água - NDWI e Índice de Urbanização - IU) da cidade de São Carlos, São Paulo, Brasil. Os resultados evidenciaram que o modelo GWR explicou mais satisfatoriamente a variabilidade da ICUS que o modelo MQO, explicando 90% da variação da ICUS no verão, enquanto que o MQO explicou 79%. Os valores de AICc indicaram, também, superioridade do modelo GWR. As informações obtidas pelo modelo não estacionário poderão facilitar a implementação de medidas mitigadoras da ICUS. O modelo GWR mostrou-se ser eficiente para modelar a ICUS em cidade média, portanto, sugere-se que esse modelo seja utilizado em pequenas e grandes cidades brasileiras para que possa ser validado em cidades com diferentes características espaciais.
... The present study examines spatial relationships between NDVI data from the MODIS NDVI satellite data and rainfall data from CHIRPS in the Bisha Watershed in southwestern Saudi Arabia. This study area is considered sensitive to environmental changes because it exists as an eco-climatic transition zone between cold semi-arid and hot arid climates (extended from south to north) [30,54,55]. According to the "Köppen climate classification [56,57]" transition areas, which are usually semi-arid and change from subhumid climates to desert climates, have semi-arid climates, as well as certain ecological characteristics that transition between them. ...
Citation: Mallick, J.; AlMesfer, M.K.; Singh, V.P.; Falqi, I.I.; Singh, C.K.; Alsubih, M.; Kahla, N.B. Evaluating the NDVI-Rainfall Relationship in Bisha Watershed, Saudi Arabia Using Non-Stationary Modeling Technique. Atmosphere 2021, 12, 593. https://
... Altitude is an important factor of topography, and the relationship between altitude and precipitable water has always been the focus of topographic precipitation research [31][32][33]. Due to the topographic effect, precipitable water and cloud droplets in complex terrain areas increase with increasing altitude. In the southern Himalayas, precipitation also has similar characteristics. ...
Changes in atmospheric water vapor mainly occur in the atmospheric boundary layer. However, due to many factors, such as orography and ground thermal dynamic conditions, the change trends and transformation law of atmospheric water vapor contents above different surfaces are still unclear. In this work, a Doppler weather radar with high spatial-temporal resolution was used to monitor the variations and transformations of water vapor contents over different land surfaces for two years. The results show that the atmospheric water vapor content shows a very good positive correlation with elevation at altitudes between 600 m and 1200 m, while different land surfaces have delicate impacts on atmospheric water vapor contents, such as extreme values appearing above impervious urban surfaces, uniform distributions appearing over water body and vegetated surfaces being wet but avoiding extreme conditions. Compared with previous studies, the results and conclusions of this study are mainly derived from accurate direct observations based on high-resolution radar. Identifying the distribution and transformation of water vapor over different surfaces can enhance our understanding of the movement and variation of atmospheric water vapor over complex terrain and different land surfaces, and improve the planning and construction capacity of different surfaces, such that humankind can mitigate the severe disasters caused by drastic changes in atmospheric water vapor.
... In fact, the amount of rainfall on the western slopes decreases to the north direction due to the formation of the winter monsoon. The rainfall decreases on the other eastern side of the mountain as the winds transporting moisture from the Red Sea are blocked by the mountain high elevations (Abdulrazzak et al. 1995;Al-Ahmadi and Al-Ahmadi 2014). Subyani (1999) reported that the Pearson correlation coefficient, between the elevation and the precipitation, was found to be significant, reaching 0.45 in the southwestern of Saudi Arabia. ...
The hydrologists need effective procedures to assist them in predicting the implications related to high rainfall risks, both at gauged and ungauged areas. The first step for any assessment is estimating the rainfall values associated with various return periods in years. This information is obtained using rainfall frequency analysis techniques based on observed maximum daily rainfall values. The existence of a regional distribution for the rainfall frequency within a certain region is considered as a precious information for the hydrologists to estimate—with confidence—the expected rainfall at high return periods. The aim of this research is to determine the regional statistical distribution for various regions in Saudi Arabia. Saudi Arabia was selected to represent arid regions as it covers a large area of the Arabian Peninsula in addition to the availability of rainfall data compared with other similar countries. The data of 394 rainfall gauging stations were included in the study, which covers all Saudi Arabia in its 13 main regions. The data was analyzed using multiple frequency analysis methods and was subjected to various statistical tests including Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), Anderson-Darling Criterion (AD), Station-Year Analysis, and Index Flood Method, in order to determine the best regional statistical distribution and define the homogenous regions using regional analysis. The study concluded that the Log-Pearson type III distribution was the best model to describe the distribution of the daily maximum rainfall in the region. Saudi Arabia was sub-divided into seven homogeneous regions. Contour maps for the 2-, 5-, 10-, 25-, 50-, and 100-year rainfall were produced to predict the rainfall at any point within the Kingdom of Saudi Arabia.
... Among the orographic factors, elevation differences considerably influence the spatial variability of climatic rainfall in mountainous terrains (Al, 2013;Basist et al., 1994;Goovaerts, 2000;Sarmadi et al., 2019;. Using the data from 1300 rain-gauge stations around the world, Lauscher (1976) attempted to globally investigate the relationship between mean annual rainfall and elevation, and found it has various characteristics at different latitudes; in the mid-latitudes, rainfall increases with elevation. ...
The Ili River Valley is a trumpet-like terrain facing westward. From west to east, the elevation of the valley floor increases and the width of the valley decreases. Using hourly rainfall data of 2009–2016 obtained from 100 gauge stations over the Ili River Valley, the climatic features of summer regional rainfall events (RREs) are investigated. The mean amount and frequency of rainfall during summer show considerable spatial variabilities in terms of along-valley and across-valley directions. Along the valley, the rainfall gradually increases with increasing elevations. Across the valley, the rainfall also increases from the valley floor to the northern and southern slopes. Three distinct types of RREs are identified: western-local, eastern-local, and eastward-movement RREs. The eastern-local and western-local RREs are located over the east and west of the valley, respectively. The eastern-local RREs have more numbers and longer duration than the western-local RREs, resulting in more rainfall in the east than in the west of the valley. In contrast, the eastward-movement RREs with the longest duration initiate from the west of the valley and gradually move to the east of the valley. For these RREs, the spatial distribution of the rainfall exhibits a pattern similar to that of the summer mean rainfall. These contribute to more than half of the summer total rainfall in most stations. To explain their propagation mechanisms, the circulation structures accompanying the eastward-movement RREs are analyzed. The circulation structures exhibit a consistent characteristic with that of the Central-Asia vortex/trough systems. The eastward movement of the entire circulation structures is corresponding with that of the rainfall center.
