Sources and implications of black carbon (BC) and mineral dust (MD) on two glaciers on the central Tibetan Plateau were estimated based on in situ measurements and modeling. The results indicated that BC and MD accounted for 11 +/- 1% and 4 +/- 0% of the albedo reduction relative to clean snow, while the radiative forcing varied between 11 and 196 and 1-89 W m(-2), respectively. Assessment of BC and MD contributions to the glacier melt can reach up 88 to 434 and 35 to 187 mm w.e., respectively, contributing 9-23 and 4-10% of the total glacier melt. A footprint analysis indicated that BC and MD deposited on the glaciers originated mainly from the Middle East, Central Asia, North China and South Asia during the study period. Moreover, a potentially large fraction of BC may have originated from local and regional fossil fuel combustion. This study suggests that BC and MD will enhance glacier melt and provides a scientific basis for regional mitigation efforts.

The climate change impacted glacio-hydrological regime and thus the availability of water resources in arid region of Central Asia. The effects of climate change in the magnitude or seasonality of regional glacier runoff were still poorly understood in Central Asia. In this study, the glacier runoff, components of glacier runoff, equilibrium line altitude (ELA) and Glacier Mass Balance (GMB) during 1959-2017 are evaluated by elevation-dependent Degree-Day glacier melt model in eight sub-basins of Tarim Basin over Central Asia. The impacts of climate change on glacier and hydrology are assessed. The results suggested that climatic regime shifted to more warm-wet pattern on glacier zone after 1990 in study area. The ablation and accumulation of glaciers showed different patterns in eight sub-basins. All sub-basins showed a glacier mass deficit and GMB displayed a marked decreasing trend, but also exhibiting discrepancy. The mean ELA and rising rate of ELA were higher in the southern region. The glacier runoff increased significantly after 1990 in Tarim Basin, with obviously temporal and spatial variations in sub-basins. The mean annual volume of glacier runoff was 175.8 x 108 m3. The ice melt was a larger component of glacial runoff in Tarim Basin. The influence of rainfall runoff on glacier runoff was more obviously than snow melt runoff as more precipitation fell as rain in northern region. The larger proportions of snow melt runoff imply more precipitation fell as snowfall in southern region. The elevation-dependent contributions in glacier runoff showed differences in individual basins. Temperature and precipitation played different role for the glacier runoff increases among the sub-basins. Differences in sensitivity of GMB and glacier runoff were distinct and vary considerably. A thorough assessment of the spatially and temporally varying melt water originated by glaciers is crucial for the success of water scarcity adaptation under climate change. The glacier mass balance displayed a marked decreasing trend in Tarim Basin of Central Asia. The mean equilibrium line altitude and its rising rate were higher in the southern region. The ice melt runoff, snow melt runoff, rainfall runoff and glacier runoff exhibited normal distribution along with increasing elevation. The glacier runoff was 175.8x108m3, with obviously temporal and spatial variations of components in sub-basins, which varied considerably in response to warm-wet climate in Tarim Basin.image

In contrast to widespread glacier retreat evidenced globally, glaciers in the Karakoram region have exhibited positive mass balances and general glacier stability over the past decade. Snow and glacier meltwater from the Karakoram and the western Himalayas, which supplies the Indus River Basin, provide an essential source of water to more than 215 million people, either directly, as potable water, or indirectly, through hydroelectric generation and irrigation for crops. This study focuses on water resources in the Upper Indus Basin (UIB) which combines the ranges of the Hindukush, Karakoram and Himalaya (HKH). Specifically, we focus on the Gilgit River Basin (GRB) to inform more sustainable water use policy at the sub-basin scale. We employ two degree-day approaches, the Spatial Processes in Hydrology (SPHY) and Snowmelt Runoff Model (SRM), to simulate runoff in the GRB during 2001-2012. The performance of SRM was poor during July and August, the period when glacier melt contribution typically dominates runoff. Consequently, SPHY outperformed SRM, likely attributable to SPHY's ability to discriminate between glacier, snow, and rainfall contributions to runoff during the ablation period. The average simulated runoff revealed the prevalent snowmelt contribution as 62%, followed by the glacier melt 28% and rainfall 10% in GRB. We also assessed the potential impact of climate change on future water resources, based on two Representative Concentration Pathways (RCP) (RCP 4.5 and RCP 8.5). We estimate that summer flows are projected to increase by between 5.6% and 19.8% due to increased temperatures of between 0.7 and 2.6 degrees C over the period 2039-2070. If realized, increased summer flows in the region could prove beneficial for a range of sectors, but only over the short to medium term and if not associated with extreme events. Long-term projections indicate declining water resources in the region in terms of snow and glacier melt.

Global warming potentially increases precipitation and intensifies water exchange, thereby accelerating the hydrological cycle. The Tibetan Plateau (TP) is an Asian water tower in which the water budget varies and its anomaly exerts stress on resource availability. Few studies have quantified long-term water budgets across TP owing to scarcity of ground-based observations and uncertainties in remote sensing data. In this study, water budget components (i.e., precipitation, glacial melting [GM], evapotranspiration [ET], runoff, and soil moisture [SM] state) in TP are synthetically estimated for the past three decades. The water budget estimation benefits from a GM-coupled hydrological ensemble modeling, which is forced by nine precipitation products with seven from satellite methods. The results show that the ensemble modeling effectively captures the dynamics of runoff, ET, and terrestrial water storage. The long-term average annual water input (sum of precipitation and GM) was approximately 438 mm, with similar to 4 % contribution from GM, for which the annual ET and runoff take away was approximately 263 and 173 mm, respectively. From 1984 to 2015, the four water fluxes significantly increased with varying rates (2.3 mm/yr, precipitation; 0.9 mm/yr, GM; 1.5 mm/yr, ET; 1.1 mm/yr, runoff), which suggested an accelerating hydrological cycle. Particularly, increasing GM (similar to 5.8 mm/yr) in the Nyainqentanglha Mountains in southern TP induced high-yield runoff (>800 mm). These estimations aid in yielding robust solutions for water management in TP and neighboring regions. The accelerated hydrological cycle implies potential flooding risk and vulnerability of the hydrological system under climate change.

Brown carbon (BrC)/water-soluble organic carbon (WSOC) plays a crucial role in glacier melting. A quantitative evaluation of the light absorption characteristics of WSOC on glacier melting is urgently needed, as the WSOC release from glaciers potentially affects the hydrological cycle, downstream ecological balance, and the global carbon cycle. In this work, the optical properties and composition of WSOC in surface snow/ice on four Tibetan Plateau (TP) glaciers were investigated using a three-dimensional fluorescence spectrometer and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The total light-absorption of WSOC in snow/ice at 250-400 nm (ultraviolet region) and 400-600 nm (visible region) accounted for about 60.42% and 27.17% of the light absorption by the total organics, respectively. Two protein-like substances (PRLIS), one humic-like substance (HULIS), and one undefined species of chromophores in snow/ice on the TP glacier surfaces were identified. The lignins and lipids were the main compounds in the TP glaciers and were presented as CHO and CHNO molecules, while CHNOS molecules were only observed in the southeast TP glacier. The light absorption capacity of WSOC in snow/ice was mainly affected by their oxidizing properties. PRLIS and undefined species were closely linked to microbial sources and the local environment of the glaciers (lignins and lipids), while HULIS was significantly affected by anthropogenic emissions (protein/amino sugars). Radiative forcing (RF)-induced by WSOC relative to black carbon were accounted for about 11.62 +/- 12.07% and 8.40 +/- 10.37% in surface snow and granular ice, respectively. The RF was estimated to be 1.14 and 6.36 W m- 2 in surface snow and granular ice, respectively, during the melt season in the central TP glacier. These findings contribute to our understanding of WSOC's impact on glaciers and could serve as a baseline for WSOC research in cryospheric science.

Monitoring the variations in terrestrial water storage (TWS) is crucial for understanding the regional hydrological processes, which helps to allocate and manage basin-scale water resources efficiently. In this study, the impacts of climate change, glacier mass loss, and human activities on the variations in TWS of the Qaidam Basin over the period of 2002-2020 were investigated by using Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) data, and other hydrological and meteorological data. The results indicate that TWS anomalies (TWSA) derived from five GRACE solutions experienced significant increasing trends over the study period, with the change rates ranging from 4.85 to 6.90 mm/year (1.37 to 1.95 km(3)/year). The GRACE TWSA averaged from different GRACE solutions exhibited an increase at a rate of 5.83 +/- 0.12 mm/year (1.65 +/- 0.03 km(3)/year). Trends in individual components of TWS indicate that the increase in soil moisture (7.65 mm/year) contributed the most to the variations in TWS. Through comprehensive analysis, it was found that the temporal variations in TWS of the Qaidam Basin were dominated by the variations in precipitation, and the spatial variations in TWS of the Qaidam Basin were mostly driven by the increase in glacier meltwater due to climate warming, particularly in the Narin Gol Basin. In addition, the water consumption associated with human activities had relatively fewer impacts.

Large-scale glaciers in the Third Pole are experiencing significant thinning and retreat, partly due to the increased deposition of black carbon (BC) and mineral dust (MD). At present, BC is generally considered a more important contributing factor than MD to glacier melting. Based on a deep analysis of published data, the relative contribution of MD versus BC to snow/ice melting increases rapidly, because BC is more likely than MD to be discharged during the melting process. As a result, the contribution of MD to glacier melting is comparable to or even higher than that of BC when the glacier surface appears as aged snow and bare ice. The importance of MD to glacier melting must therefore be emphasized in the water tower of Asia.

In many high altitude river basins, the hydro-climatic regimes and the spatial and temporal distribution of precipitation are little known, complicating efforts to quantify current and future water availability. Scarce, or non-existent, gauged observations at high altitudes coupled with complex weather systems and orographic effects further prevent a realistic and comprehensive assessment of precipitation. Quantifying the contribution from seasonal snow and glacier melt to the river runoff for a high altitude, melt dependent region is especially difficult. Global scale precipitation products, in combination with precipitation-runoff modelling may provide insights to the hydro-climatic regimes for such data scarce regions. In this study two global precipitation products; the high resolution (0.1 degrees x 0.1 degrees), newly developed ERA5-Land, and a coarser resolution (0.55 degrees x 0.55 degrees) JRA-55, are used to simulate snow/glacier melts and runoff for the Gilgit Basin, a sub-basin of the Indus. A hydrological precipitation-runoff model, the Distance Distribution Dynamics (DDD), requires minimum input data and was developed for snow dominated catchments. The mean of total annual precipitation from 1995 to 2010 data was estimated at 888 mm and 951 mm by ERA5-Land and JRA-55, respectively. The daily runoff simulation obtained a Kling Gupta efficiency (KGE) of 0.78 and 0.72 with ERA5-Land and JRA-55 based simulations, respectively. The simulated snow cover area (SCA) was validated using MODIS SCA and the results are quite promising on daily, monthly and annual scales. Our result showed an overall contribution to the river flow as about 26% from rainfall, 37-38% from snow melt, 31% from glacier melt and 5% from soil moisture. These melt simulations are in good agreement with the overall hydro-climatic regimes and seasonality of the area. The proxy energy balance approach in the DDD model, used to estimate snow melt and evapotranspiration, showed robust behaviour and potential for being employed in data poor basins. (c) 2021 Published by Elsevier B.V.

Commonly known as the Asian Water Tower, glaciers in the Tibetan Plateau (TP) and its surrounding regions are vital to the regional water cycle and water resources in the downstream areas. Recently, these glaciers have been experiencing significant shrinkage mostly due to climate warming, which is also profoundly modulated by the surface snow albedos. In this study, we summarized the current status of the glaciers in the TP and its sur-rounding region, focusing on glacier retreat and mass balance. Furthermore, based on glacier surface snow al-bedo data retrieved from MODIS (moderate resolution imaging spectroradiometer, with resolution of 500 m x 500 m), we investigated the potential impact of glacier surface snow albedo changes on glacier melting. The results demonstrated that glacier shrinkage was pronounced over the Himalayas and the southeast TP. The regional distribution of the average albedos on the glacier surface (during summer) exhibited similar patterns to those of glacier retreat and mass balance changes, indicating a significant relationship between the annual glacier mass balance and glacier surface albedos during the past decades (2001-2018). This reflected that albedo reduction, in addition with rising temperatures and changing precipitation, was a significant driver of glacier melting in the TP. Estimations based on glacier surface summer albedos and snowmelt model further suggested that the effect of surface albedo reduction can drive about 30% to 60% of glacier melting. Due to its strong light absorption, black carbon (BC) in snow can be a substantial contributor to albedo reduction, which enhanced glacier melting in summer in the TP by approximately 15%. This study improved our insights into the causes of glacier melting in the Tibetan Plateau.

Most glaciers in the Tibetan Plateau (TP) are experiencing dramatic retreat, which is resulting in serious environmental and ecological consequences. In addition to temperature increases, increased light-absorbing particles (LAPs) and decreased precipitation were proposed to, independently, play important roles in reducing glacier accumulation. Based on investigations of effect from an extremely low precipitation event in the TP and surrounding regions caused by La Nina from October 2020 to April 2021, a new mechanism was provided. It was shown that decreased precipitation during study period leaded to both low snow accumulation and high LAP concentrations in snow on glacier surfaces in the TP. This phenomenon will strongly enhance earlier and accelerated glacier melt in this critical region and needs to be considered in future related studies. (C) 2021 Elsevier B.V. All rights reserved.