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Air Temperature Lapse Rate between Automatic Weather Station (AWS)1 and AWS2; and (b) Comparison of Observed and Simulated Hourly Air Temperature at AWS2.
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Most glaciers in the Tibetan Plateau (TP) are not closely monitored for mass balance (MB) due to their inaccessibility, which makes it difficult to better understand the dynamics of glacial advancement or retreat. Surface energy budget, MB, and the resulting melt runoff were calculated for Zhadang glacier (5,710 m above sea level) of the central TP...
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... three-hour gauge data were then converted to hourly data equally. The vertical air temperature lapse rate between AWS1 and AWS2 was analyzed, indicating that there is a good correla- tion ( Figure 2a). Thus, the lapse rate of À1.01°C/ 100 m was used. ...
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... the sites of AWS1 and AWS2, the empirical relationships between daily maximum (or minimum) and daily average air tem- peratures were developed using observed data during respectively. The applicability of this disaggregation method was validated with the observed hourly data at AWS2 for the period of June-October 2007 ( Figure 2b). As shown in Figure 3a, wind speed at AWS2 tended to be greater than at AWS1, probably because AWS2 is located at the col. ...
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... • C −1 ) and 10% precipitation increase (m w.e. (10%) −1 ) of different glaciers across the Tibetan Plateau [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88]. Section S1: Surface energy-mass balance model. ...
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... It is worth noting that around 24% of the modeling basin cases did not involve a parameter calibration procedure (such as Gaddam et al., 2018;Zhang et al., 2020); those studies typically used simple hydrological models and estimated parameter values based on field surveys and prior knowledge (e.g., Wang et al., 2015a;Kumar et al., 2016), or used a physically-based energy-balance module for the calculation of melt runoff (e.g., Prasch et al., 2011;Bash and Marshall, 2014;Brown et al., 2014). In total, the temperature-index (also named as degree-day) method was used in about 94% of the 227 modeling cases to calculate melt runoff (i.e., Koboltschnig et al., 2007;Singh et al., 2008;Zhang and Zhang, 2009;Li et al., 2014;Adnan et al., 2017), while the energy-balance approach was used in the remaining 6% (e.g., Loukas et al., 2002;Dadic et al., 2008, Li et al., 2015. ...
Quantifying the contributions of runoff components (CRCs) to streamflow is of significant importance for understanding the dynamics of water resources under changing climate in glacierized basins. This article presents a meta-analysis on different approaches for quantifying runoff components in glacierized basins, including the tracer-based end-member mixing method and the hydrological modeling approach. We collected estimated CRCs from 312 glacierized basin cases, as well as values of five characteristics in these basins including mean basin elevation (MBE), mean annual air temperature (MAT), mean annual precipitation (MAP), winter precipitation fraction (WPF) and glacierized area ratio (GAR). Relations between CRCs and the basin characteristics were assessed using a random forest (RF) algorithm. The review showed that CRCs were most often quantified by the hydrological modeling approach (73% of the basin cases). Compared to hydrological modeling, the tracer-based approach (applied in 19% of the basin cases) was more likely to be used in smaller basins <50 km², rather at the seasonal than annual time scale and with shorter study periods of <=5 years. Meta-analysis results indicate that: (1) At the annual time scale, the most important influencing basin characteristics were GAR and MBE for the ice melt contribution, WPF and MAP for the snow melt contribution, and GAR and WPF for the rainfall contribution. RF algorithm based on the five basin characteristics was able to explain 56%, 40%, and 40% of the variability of the reported annual contributions of ice melt, snowmelt and rainfall, respectively; the variability of seasonal CRCs and annual contribution of groundwater could be less well explained by the five basin characteristics. (2) Comparing different definitions of runoff components based on water-input or flow-pathway indicated that the ice melt contribution to total water input (sum of rainfall and melt water) based on the water-input definition was close to the contribution of ice melt-induced surface flow to total runoff based on the flow-pathway definition. In contrast, based on the reviewed studies, rainfall and snowmelt contributions based on the water-input definition were around 9%-14% higher than the contributions of rainfall and snowmelt induced surface flow to total runoff. (3) The tracer-based end-member mixing method tended to estimate larger uncertainties of CRCs than hydrological modeling, but uncertainties of modeled CRCs were likely underestimated as often only one or two of the three uncertainty sources of model parameter, model input and model structure were considered in the modeling studies. We propose that more efforts are required to cross validate CRCs estimated by the tracer-based and hydrological modeling methods, and to reduce uncertainties of CRCs by integrations of hydro-meteorological data and water tracer data.
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Research Impact Statement: Critical zone controls larger portion of variability in meltwater and runoff, whereas temperature change is identified as dominant driver for total runoff changes in most of the glacierized catchments. ABSTRACT: In glacierized catchments, elevation is correlated with meltwater through its association with temperature , precipitation, and glacier hypsometry. The revelation of the altitudinal distribution of meltwater, unattended and not fully understood in previous work, might provide a better understanding of climate change impacts on glacio-hydrology. Here, critical zone approach was defined and applied in 12 glacierized catchments of the Tien Shan-Pamir-Karakorum Mountains, Central Asia using manually calibrated glacier-enhanced Soil and Water Assessment Tool model over 1966-2005. The critical zone, a sequence of elevation bands with above-average snow and glacier melt, contributes maximum meltwater to total runoff. The critical zone shared 37%-95% (average = 80%) of meltwater contributions to total runoff, although its size was only 13%-30% of the total elevational relief. The critical zone controlled 76% and 82% variability in relative changes of glacier area and total runoff at the catchment scale, respectively. The increase in temperature was identified as the dominant driver for variations in total runoff in all catchments except Vakhsh and Yurungkash, where precipitation change remained dominant. Overall, glacier hypsometry limited the first-order control of meltwater distributions on glacio-hydrology. It is concluded that critical zone approach can interpret the proxy role of elevation to affect water availability under climate and glacier area change in glacierized catchments. (
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Glacier mass balance shows a spatially heterogeneous pattern in response to global warming on the Tibetan Plateau (TP), and the climate mechanisms controlling this pattern require further study. In this study, three glaciers where systematic glaciological and meteorological observations have been carried out were selected, specifically Parlung No. 4 (PL04) and Zhadang (ZD) glaciers on the southern TP and Muztag Ata No. 15 (MZ15) glacier in the eastern Pamir. The characteristics of the mass and energy balances of these three glaciers during the periods between October 1th, 2008 and September 23rd, 2013 were analyzed and compared using the energy and mass balance model. Results show that differences in surface melt, which mainly result from differences in the amounts of incoming longwave radiation (Lin) and outgoing shortwave radiation (Sout), represent the largest source of the observed differences in mass balance changes between PL04 and ZD glaciers and MZ15 glacier, where air temperature, humidity, precipitation and cloudiness are dramatically different. In addition, sensitivity experiments show that mass balance sensitivity to air temperature change is remarkably higher than that associated with precipitation change on PL04 and ZD glaciers, in contrast results from MZ15 glacier. And significantly higher sensitivities to air temperature change are noted for PL04 and ZD glaciers than for MZ15 glacier. These significant differences in the sensitivities to air temperature change are mainly caused by differences in the ratio of snowfall to precipitation during the ablation season, melt energy (Lin+Sout) during the ablation season and the seasonality of precipitation among the different regions occupied by glaciers. In turn, these conditions are related to local climatic conditions, especially air temperature. These factors can be used to explain the different patterns of change in Tibetan glacier mass balance under global warming.
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... tpedatabase.cn) and previous studies (Li et al., 2015;Zhang et al., 2013a). The initial snow cover map was simply set to 10 cm w.e. because such uncertainty in initial inputs could be largely reduced after model running for several mass balance years. ...
Understanding the hydrologic processes of inland lake basins in the Tibetan Plateau (TP) could provide insights into the responses of Tibetan lake dynamics to climate change. An efficient approach for this purpose is to represent complex hydrologic behaviors of such Tibetan lake watersheds with plausible hydrologic models. In this study, water level fluctuations of Lake Nam Co, an inland lake in the central TP, were investigated using a lumped lake-watershed model. The degree-day factor method was introduced to improve the model applicability in glacier-covered basins. The model simulated the hydrologic processes as well as the lake water budget. Remote sensing images (Landsat MSS, TM, ETM + and OLI) from 1972 to 2015 were used to identify the glacier and lake boundaries. Multisource climate data (e.g., ground point observation, 0.25o gridded APHRODITE and TRMM 3B42 v7 precipitation products) were used to drive the hydrologic model at a monthly time step. Results of trend analysis showed that basin-wide annual air temperature increased by the rate 0.04 °C/yr from 1961 to 2015. Mean annual precipitation slowly increased from 1961 to the mid-1990s, and then rapidly increased from the late-1990s to the mid-2000s, and finally obviously decreased after the mid-2000s. As a response to climate change, glaciers decreased by 62.69 km² (29%) and lake area increased by 91.83 km² (4.7%) from 1972 to 2015. The analysis of lake water budget suggested that, the total basin runoff and on-lake precipitation contributed 1.36 km³/yr (66%) and 0.7 km³/yr (34%), respectively, to mean annual water gain of the lake. Glacier runoff was 14% of the basin runoff and 10% of the total water gain of the lake. The percentages of lake evaporation, water seepage and water surplus were 65%, 20% and 15%, respectively. Lake level increased with the rate of 0.14 m/yr for the study period 1961–2015. It could be concluded that precipitation was the dominant controlling factor for the different magnitudes of lake level rising rates of 0.10, 0.41 and 0.06 m/yr for the periods of 1961–1998, 1999–2008 and 2009–2015, respectively.
Global climate change gives rise to changing spatial patterns of snow and ice, especially over mountain blocks where orographic and synoptic circulation effects play significant roles in creating patterns of precipitation and glacier development. The presence of snow and ice results in heat balance changes and other land surface feedbacks that have implications for patterns of mountain glacier retreat and the dynamics of mountain geomorphic systems. This study considers the sensitivity of the mountain cryosphere (snow, ice, permafrost) to global climate change, and the implications of this sensitivity analysis for evaluating mountain surface stability, geomorphic change and the generation of mountain geohazards. Consideration of these issues is informed by evidence from case studies reported in the literature and by field observations of mountain system dynamics worldwide. Results show that ‘sensitivity’ to climate forcing has been interpreted and defined in different ways in mountain snow, ice and permafrost systems, with respect to properties such as albedo, mass balance or rapidity of system change. There are also significant spatial differences in sensitivity between different mountain blocks for snow, ice and permafrost, and these regions are therefore likely to follow different trajectories of geomorphic change in response to climate forcing, related to their physiographic properties and the extent of cryospheric coverage. Within glaciated mountains in particular, the relative timing of different geomorphic events, and the interplay between slope, glacier front and proglacial sediment sources and environments, may vary depending on glacier size, geomorphic setting and microclimate. By contrast, responses to permafrost warming (increased surface instability and mass movements) and changes in snow patterns (avalanche risk, floods) may have quite different spatial and temporal patterns and influenced by different environmental controls. An integrated evolutionary model for mountain system development under a changing cryosphere is proposed, highlighting the critical role of energy balance as a forcing factor that then triggers downstream mountain system responses. This suggests that different elements of mountain systems exhibit different sensitivities, and furthermore that these sensitivities change over time and space through the period of anthropogenic global warming and paraglacial relaxation.
Understanding glacier mass balance (MB) change under global warming is important to assess the impact of glacier change on water resources. This study evaluated the applicability of a modified distributed surface energy balance model (DSEBM) with 3-h temporal and 100-m spatial resolution to the alpine Dongkemadi Glacier (DKMD) in the central Tibetan Plateau region, analyzed the causes of glacier MB variations with respect to energy balance, and evaluated MB changes under various climate scenarios. Results showed that: (i) the modified model can describe surface energy and MB of XDKMD well; (ii) net shortwave and longwave radiation, accounting for more than 80% of total heat flux, dominated the glacier energy balance during both summer and winter months; (iii) summer MB spatial patterns dominated annual MB, consistent with the fact that DKMD is a summer accumulation type glacier; and (iv) effect of increase in air temperature on glacier MB is higher than that of decrease in air temperature. The sensitivity of MB revealed by the modified DSEBM can help to understand MB changes influenced by the climate changes and to regulate water management strategies to adapt to climate changes at the catchment scale.
Few simulations of typical Tibetan Plateau glacier response to climate warming have been made, despite the glaciers' importance as water supplies in an arid region. Here we apply a three-dimensional thermomechanically coupled full-Stokes ice dynamics model to simulate the evolution of Qingtang No.1 Glacier, a representative glacier in the central Tibetan Plateau. A degree-day model along with snow temperature and precipitation estimates based on nearby observations are used to estimate surface mass balance (SMB) over the past three decades. The resulting SMB gradients and equilibrium-line altitude (ELA) sensitivity to air temperature are used to parameterize the SMB in the future. We use the ice-flow model to simulate glacier evolution from 2013 to 2050. Simulated within-glacier temperatures and present-day glacier terminus retreat rates are in reasonable agreement with previous observations. Forcing the glacier model with the historical warming trend of 0.035 degrees Ca-1 and a warming projection from the high resolution regional climate model (RegCM3) under the A1B scenario for the period 2013-2050 leads to substantial retreat and ice loss, and large increases (110%-155%) in annual water runoff. Losses of 11%-18% in area and 19%-30% in volume are predicted over the next four decades, with the warmer RegCM3 scenario giving larger rates of loss. Sensitivity of glacier change to the parameters in SMB profiles are also assessed.
