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.

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.

Cloud is an active component in the weather-climate system that modulates both the radiation balance and the water cycle of the earth system via physical, chemical, and radiative mechanisms. In this study, we used observations of meteorological variables recorded on the Laohugou Glacier No. 12 in the western Qilian Mountains during 2009-2017 to investigate the radiative properties of cloud and its impact on glacier melting. The quantified cloud fraction showed an evident seasonal cycle. The highest cloudiness typically occurred at 16:00 Beijing time, which was probably associated with the strength of local convection that produced frequent occurrence of low-level cumulus or cumulonimbus clouds. Most heavy precipitation events (>14 mm) occurred on overcast days, signified that at least half of the total precipitation could be attributed to transportation from meso- or large-scale atmospheric circulations. Relationships between modelled glacier melting, energy components and cloud fraction showed that clouds could importantly reduce glacier melting, the most important contributor to this process was the clouds impact on net shortwave radiation. Circulation analyses showed that similar to 7.8%, similar to 6.3%, and similar to 18.7% of overcast days could be clearly and uniquely attributed to Arctic air mass events, monsoon events, and westerlies events, respectively. The remaining overcast days (similar to 67.2%) were influenced by multiple circulations, e.g., westerlies-monsoon, westerlies-Arctic air mass, monsoon-Arctic air mass, and westerlies-monsoon-Arctic air mass interactions. Monsoon potentially contributes a lot to precipitation in the western Qilian Mountains, future work should aim to do more atmospheric circulation analyses combining with isotopic tracing when precipitation occurs during overcast days.

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.

Solid precipitation is not only the main supply for glacier mass, but also exerts an important influence on surface albedo and intensifies glacier melting. However, precipitation type observation is very scarce in the high alpine glaciers, which limits the precise simulation of glacier mass balance. This study assessed three discrimination methods of precipitation types including Ding method, Dai method and Froidurot method based on surface albedo observation data on the Laohugou Glacier No. 12 (LHG Glacier) in western Qilian Mountains. The results showed that Ding method had a best applicability on the LHG Glacier, the other two need to calibrate parameters when they are used in the high elevation glacier region. Then we fitted the relationship between snowfall probability and fresh snow albedo, and put forward a revised formula to simulate fresh snow albedo based on Ding method, which is expected to reduce the uncertainty in glacier mass and energy balance model. Finally, we found a best air temperature threshold of 4 degrees C for discriminating monthly precipitation types. In order to accurately simulate the glacier melt, it is necessary to obtain the threshold temperature appropriately in different glacier region with different elevation and humidity.

Light-absorbing impurities (LAIs), such as organic carbon (OC), black carbon (BC), and mineral dust (MD), deposited on the surface snow of glacier can reduce the surface albedo. As there exists insufficient knowledge to completely characterize LAIs variations and difference in LAIs distributions, it is essential to investigate the behaviors of LAIs and their influence on the glaciers across the Tibetan Plateau (TP). Therefore, surface snow and snowpit samples were collected during September 2014 to September 2015 from Zhadang (ZD) glacier in the southern TP to investigate the role of LAIs in the glacier. LAIs concentrations were observed to be higher in surface aged snow than in the fresh snow possibly due to post-depositional processes such as melting or sublimation. The LAIs concentrations showed a significant spatial distribution and marked negative relationship with elevation. Impurity concentrations varied significantly with depth in the vertical profile of the snowpit, with maximum LAIs concentrations frequently occurred in the distinct dust layers which were deposited in non monsoon, and the bottom of snowpit due to the eluviation in monsoon. Major ions in snowpit and backward trajectory analysis indicated that regional activities and South Asian emissions were the major sources. According to the SNow ICe Aerosol Radiative (SNICAR) model, the average simulated albedo caused by MD and BC in aged snow collected on 31 May 2015 accounts for about 13% +/- 3% and 46% +/- 2% of the albedo reduction. Furthermore, we also found that instantaneous RF caused by MD and BC in aged snow collected on 31 May 2015 varied between 4-16 W m(-2) and 7-64 W m(-2), respectively. The effect of BC exceeds that of MD on albedo reduction and instantaneous RF in the study area, indicating that BC played a major role on the surface of the ZD glacier.