The Asian water tower (AWT) serves as the source of 10 major Asian river systems and supports the lives of ~2 billion people. Obtaining reliable precipitation data over the AWT is a prerequisite for understanding the water cycle within this pivotal region. Here, we quantitatively reveal that the \"observed\" precipitation over the AWT is considerably underestimated in view of observational evidence from three water cycle components, namely, evapotranspiration, runoff, and accumulated snow. We found that three paradoxes appear if the so-called observed precipitation is corrected, namely, actual evapotranspiration exceeding precipitation, unrealistically high runoff coefficients, and accumulated snow water equivalent exceeding contemporaneous precipitation. We then explain the cause of precipitation underestimation from instrumental error caused by wind-induced gauge undercatch and the representativeness error caused by sparse-uneven gauge density and the complexity of local surface conditions. These findings require us to rethink previous results concerning the water cycle, prompting the study to discuss potential solutions.

The Qinghai-Tibet Plateau (QTP) is characterized by a vast number of frozen and unfrozen freshwater reservoirs, which is why it is also called \"the third pole\" of the Earth or \"Asian Water Tower\". We analyzed testate amoeba (TA) biodiversity and corresponding protozoic biosilicification in lake sediments of the QTP in relation to environmental properties (freshwater conditions, elevation, and climate). As TA are known as excellent bio-indicators, our results allowed us to derive conclusions about the influence of climate warming on TA communities and microbial biogeochemical silicon (Si) cycling. We found a total of 113 TA taxa including some rare and one unknown species in the analyzed lake sediments of the QTP highlighting the potential of this remote region for TA biodiversity. >1/3 of the identified TA taxa were relatively small (<30 μm) reflecting the relatively harsh environmental conditions in the examined lakes. TA communities were strongly affected by physico-chemical properties of the lakes, especially water temperature and pH, but also elevation and climate conditions (temperature, precipitation). Our study reveals climate-related changes in TA biodiversity with consequences for protozoic biosilicification. As the warming trend in the QTP is two to three times faster compared to the global average, our results provide not only deeper insights into the relations between TA biodiversity and environmental properties, but also predictions of future developments in other regions of the world. Moreover, our results provide fundamental data for paleolimnological reconstructions. Thus, examining the QTP is helpful to understand microbial biogeochemical Si cycling in the past, present, and future.

Recent studies indicate that the Asian Water Tower (AWT) is at risk due to climate change, which can negatively impact water and food security in Asia. However, there is a lack of comprehensive information on lakes\' spatial and temporal changes in this region. This information is crucial for understanding the risk magnitude and designing strategies. To fill this research gap, we analyzed 89,480 Landsat images from 1977 ± 2 to 2020 ± 2 to investigate the changes in the size of lakes recharged by the AWT. Our findings showed that out of the 209 lakes larger than 50 km2, 176 (84 %) grew during the wet season and 167 (81 %) during the dry season. 74 % of expanded lakes are located in the Inner Tibetan Plateau (TP) and Tarim basins. The lakes that shrank are found mainly in the Helmand, Indus, and Yangtze basins. Over the entire period, the area of shrinkage (55,077.028 km2 in wet season, 53,986.796 km2 in dry) markedly exceeded expansion (13,000.267 km2 in wet, 11,038.805 km2 in dry), with the drastic decline of the Aral Sea being a major contributor to shrinkage, accounting for 90 % of the total loss. From 1990 ± 2 to 2020 ± 2, alpine lakes mostly expanded, plain lakes mostly shrank, with the opposite trend from 1977 ± 2 to 1990 ± 2. Glacial loss and permafrost thawing under global warming in the Inner TP, Tarim Interior, Syr Darya, and Mekong basins were strongly correlated with lake expansion. However, permafrost discontinuities may prevent significant growth of lakes in the Indus and Ganges basins despite increased recharge. Our findings point to the prominence of the risk the lakes recharged by AWT face. Taking immediate action to manage these risks and adaptation is crucial as the AWT retreats and lake recharges are slowed.

Climate change and human activities can have an impact on the supply and demand of water-related ecosystem services (WRESs) in the Asian water tower (AWT) and its downstream area, which is closely related to the production and livelihoods of billions of people. However, few studies have taken the AWT and its downstream area as a whole to assess the supply-demand relationship of WRESs. This study aims to assess the future trends of the supply-demand relationship of WRESs in the AWT and its downstream area. Here, the supply-demand relationship of WRESs in 2019 was assessed using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model and socio-economic data. Then, future scenarios were selected under the framework of the Scenario Model Intercomparison Project (ScenarioMIP). Finally, trends in the supply-demand of WRESs were analysed at multiple scales from 2020 to 2050. The study found that the supply-demand imbalance of WRESs in the AWT and its downstream area will continue to intensify. The area with imbalance intensification was 2.38 × 106 km2 (61.7 %). The supply-demand ratio of WRESs will decline significantly under different scenarios (p < 0.05). The main reason for the imbalance intensification in WRESs is the constant growth of human activities, with a relative contribution of 62.8 %. Our findings suggest that in addition to the pursuit of climate mitigation and adaptation, attention should also be paid to the impact of rapid human activity growth on the supply-demand imbalance of WRESs.

Determining the changes in the urban water footprint (WF) of the Tibetan Plateau is important for sustainable development within this region and in downstream regions. Taking Xining, the largest city on the Tibetan Plateau, as an example, this study quantified the changes in the WF of this region in the 2005-2018 period. We found that Xining\'s total WF increased by 22.6%, from 8.9 billion to 10.9 billion m3 in this period. The increase in Xining\'s gray WF (WFgray) resulting from the intensification of urban point-source pollution was the primary cause of the increase in its total WF. Xining\'s WFgray from point-source pollution increased by 75.3%, from 3.1 billion to 5.4 billion m3. In addition, Xining\'s WF far surpassed the amount of available water resources (WA) in this region. It is possible to prevent Xining\'s WF from exceeding its WA only by simultaneously controlling point- and nonpoint-source pollution in the future. Thus, it is recommended that great importance be attached to the rapid increase in the WFgray of the Tibetan Plateau resulting from rapid urbanization and that effective measures be implemented to control point- and nonpoint-source pollution, so as to safeguard sustainable development within the Tibetan Plateau and in downstream regions.