Understanding how precipitation responds to temperature change is critical for interpreting hydroclimate risk over the Tibetan Plateau, a high-elevation water tower supplying major Asian river systems. While global-mean precipitation increases more slowly than Clausius–Clapeyron moisture scaling, regional responses can vary strongly with circulation and topography. We assess precipitation–temperature coupling over the Tibetan Plateau using two complementary approaches. First, we quantify Tibetan Plateau hydrological sensitivity (TPHS) from 14 CMIP6 models using idealized 1pctCO₂ and PiControl experiments (1850–1999), defined as the percentage change in precipitation per degree of warming. Second, we diagnose temperature-conditioned reorganization of daily precipitation occurrence using a quality-controlled 0.25° gridded observational dataset (1970–2019), evaluating precipitation intensity percentiles conditioned on temperature percentiles. The ensemble-mean TPHS is positive and seasonally varying: 3.6 ± 0.2% °C⁻¹ annually, with seasonal values of 2.6 ± 0.7 (winter), 4.9 ± 0.4 (spring), 3.6 ± 0.3 (summer), and 3.1 ± 0.5% °C⁻¹ (autumn). Observations show a systematic redistribution toward heavier daily intensities under warmer temperature regimes, most pronounced in spring and autumn. Together, these findings indicate that warming is associated with both an enhanced regional-mean precipitation response in CMIP6 models and a shift toward more frequent high-intensity precipitation in observations over the Tibetan Plateau.

Quantifying long-term historical changes in river runoff from the vulnerable high-mountain Third Pole is critical for Asia's water resources planning, but still unresolved from a coherent, regional perspective in the climate change context. Here we show that the mountain-outlet runoff generally experienced significant increases for the westerlies-dominated rivers (Indus, Amu Darya, Syr Darya, Tarim, Heihe, and, Shule) and insignificant declines for the monsoon-dominated rivers (Ganges, Brahmaputra, Mekong, and Salween) in the past half-century, largely driven by the enhanced westerlies and weakened Indian summer monsoon. Although the changing rates of runoff can be mostly explained by the varying precipitation minus evapotranspiration, the total water storage changes (e.g., regional glacier melting, groundwater depletion) cannot be neglected. After the year 1997, the contrasting changes in the westerlies- and monsoon-dominated regions have been remarkably accelerated, necessitating proactive adaptations to sustain regional water, ecology, and food security.

Study regions: Amu Darya River, a transboundary river originated in the high mountains of Central Asia, provides water resources for 43 million people. The river is a hot spot for research and of high tension and conflicts among nearby countries. Study focus: Climate projections from 20 Earth System Models (ESMs) under SSP1–2.6, SSP2–4.5, SSP3–7.0 and SSP5–8.5 climate scenarios archived in CMIP6 were statistically downscaled and bias corrected and were used to force the Variable Infiltration Capacity (VIC) hydrological model coupled with glacier melting scheme to analyze climate change impact on streamflow during 2020–2100. Our analysis focuses on the long-term streamflow changes, seasonality of streamflow, streamflow variability, and extreme streamflow. New hydrological insights for the region: Our study shows that although annual snowmelt streamflow sharply decreases, the modeled annual total streamflow continues to rise until the middle or the end of the century caused primarily by a positive change in rainfall and accelerated glacier melt. In this melt-water -dominated basin, the future hydrology largely depends on the rainfall and glacier melt. At the seasonal scale, the earlier onset of snowmelt causes total streamflow increases in spring and early summer, but little changes in the timing of peak streamflow. Analysis of annual maximum daily flows and streamflow variability reveals increases in the intensity and frequency of extreme streamflow event and a much larger year-to-year variability due to the reduced buffering effects of snowmelt and the gradually increased contribution from rainfall. These projections indicate that mitigation measures of ensuring water security should focus on coping with seasonal streamflow shifts, high annual streamflow variability and enhanced extreme events.

Abstract. Snow in the high-altitude and high-latitude regions is essential for water resources and climate regulation. However, studies on snow mass balance components in alpine areas like the Tibetan and Pamir Plateaus (TPP) are limited. To fill the gap, a novel snow simulation framework was developed, combining in-situ snow depth, satellite snow cover, and point- and grid-scale modelling, supported by sensitivity analysis, automatic calibration, and deep learning. Key snow components—snowfall, snow water equivalent (SWE), refrozen snow, sublimation, evaporation, and snowmelt—were simulated across the TPP from 1962 to 2019 with reliable accuracy. Regionally averaged annual snowfall and refrozen snow—together representing snow pack input—were 70.67 ± 17.32 mm and 16.56 ± 3.85 mm, respectively. On average, 38 % of this input is converted into SWE and snowmelt that contributes 12–19 % of total river discharge over the TPP, while the remaining 62 % is lost to the atmosphere through sublimation and evaporation. Snow contributes less to water resources than to atmospheric moisture over the TPP on annual average. Seasonal snow patterns vary by region: in the Pamirs snow accumulates throughout the winter, making March–April SWE a key water resource indicator; while in the Tibetan Plateau, limited snow accumulation means total annual snowmelt better representing snow water resources. Significant regional declines have been simulated for key snow components though the trends vary spatially, potentially greatly influencing weather and climate both locally and remotely. Precipitation drives SWE changes in the north and west of the TPP, while temperature and wind speed play greater roles in the center and south.

Brine mining to meet resource demands amid renewable energy transitions is affecting water resources in South America and China. Hydrologists can help understand how and join the search for solutions.

Soil freeze-thaw cycles play a critical role in ecosystem, hydrological and biogeochemical processes, and climate. The Tibetan Plateau (TP) has the largest area of frozen soil that undergoes freeze-thaw cycles in the low-mid latitudes. Evidence suggests ongoing changes in seasonal freeze-thaw cycles during the past several decades on the TP. However, the status of diurnal freeze-thaw cycles (DFTC) of shallow soil and their response to climate change largely remain unknown. In this study, using in-situ observations, the latest reanalysis, machine learning, and physics-based modeling, we conducted a comprehensive assessment of the spatiotemporal variations of DFTC and their response to climate change in the upper Brahmaputra (UB) basin. About 24 +/- 8% of the basin is subjected to DFTC with a mean frequency of 87 +/- 55 days during 1980-2018. The area and frequency of DFTC show small long-term changes during 1980-2018. Air temperature impacts on the frequency of DFTC changes center mainly around the freezing point (0 degrees C). The spatial variations in the response of DFTC to air temperature can primarily be explained by three factors: precipitation (30.4%), snow depth (22.6%) and seasonal warming/cooling rates (14.9%). Both rainfall and snow events reduce diurnal fluctuations of soil temperature, subsequently reducing DFTC frequency, primarily by decreasing daytime temperature through evaporation-cooling and albedo-cooling effects, respectively. These results provide an in-depth understanding of diurnal soil freeze-thaw status and its response to climate change. Freeze-thaw transitions of terrestrial landscapes are a common phenomenon in cold regions. The seasonal and diurnal freeze-thaw cycles (DFTC) of shallow soil exhibit substantial differences in response to climate. Understanding of the spatiotemporal patterns of DFTC and their response to climate change remains limited over the Tibetan Plateau (TP), which is characterized by the largest areas of freeze-thaw terrain in the mid- and low-latitudes of the world. We found the frequency and area of DFTC show a slight increase trend in a significantly warming climate in upper Brahmaputra (UB) basin, the largest river basin of the TP. The variation of DFTC depends on climatic conditions, with soils near the freezing point (0 degrees C) being more susceptible to changes in DFTC. Precipitation, snow depth and seasonal warming/cooling rates are the top three factors influencing the response of DFTC to air temperature changes. Snowfall plays a more important role in the temporal variability of DFTC frequency than rainfall. The number of diurnal freeze-thaw cycles (DFTC) in shallow soil increase slightly during the period 1980-2018 in the upper Brahmaputra (UB) basin Air temperature effects on the changes in DFTC frequency center on the freezing point Snowfall plays a more important role in the temporal variability of DFTC than rainfall

Frozen soil properties and thermohydraulic processes are still not fully understood due to lack of in-situ measurements, especially in the high altitudes and high latitudes (HAHL). Based on hourly measurements at 10, 40, 80 and 120 cm depths at 21 sites in the west, south and northeast regions of the Tibetan Plateau (TP) during July 2018 - July 2019, we examined soil particles, spatiotemporal variations of soil thermohydraulic processes and their connections with environmental factors to reveal the heterogenous frozen soil properties on the TP. Sand and silt are the dominant soil particles and clay is less than 10% at the sites. Existing and widely used soil products underestimates (significantly overestimates) sand (clay) content on the TP which raises the uncertainty in the thermohydraulic parameters derived from these products. Diurnal soil moisture and temperature variations are seen only above 40 cm, but seasonal variations occur down to 120 cm due to the soil memory effect. Seasonally frozen soil and permafrost soil show different freezing and melting processes. Dry soil features greater soil temperature temporal variability and deeper maximum frozen depth than wet soil. Zero curtain occurs in both dry and wet soil, and displays high (low) frequency but short (long) duration at 10 (80) cm that vary spatially. Moisture depression exists in seasonally frozen soil and is determined by the initial soil moisture and temperature gradient strength. The strong thermohydraulic coupling existed in cold season collapses in warm season. Soil moisture exhibits higher spatiotemporal variability than soil temperature. At daily time scale, the influences of precipitation, wind speed and relative humidity on soil moisture and temperature vary under different climate conditions. These findings fill the knowledge gaps in the soil thermohydraulic processes in the HAHL, and improve the understanding of frozen soil properties and heat-water coupling processes in soil in the HAHL. The study will benefit the Earth system model development and improve the quality of soil temperature and moisture assimilation and remote sensing products in the HAHL.

Tibet's Qilian Mountains (QM) include critical water conservation areas and important ecological barriers, which help maintain downstream inland river oasis stability. For decades, contemporaneous climatic and cryospheric variation has severely impacted QM's hydrological processes, challenging local water resource management and sustainable development. However, due to prevalent data and methodological limitations, QM research has primarily focused on runoff change at a basin scale. Spatial distributions and temporal changes in runoff subsequently remain unclear. Based on multi‐source data and the literature, we estimated that QM's mountain outlets generate approximately 15.671 km 3 in total annual runoff, exhibiting a spatially decreasing pattern from northeast to southwest. Moreover, runoff distribution and trend variation at seasonal and annual scales depend upon the river replenishment source type. Beginning in the 1950s and 1960s, eastern rain‐fed rivers experienced a downward trend while those dominated by meltwater or simultaneously fed by multiple sources in its central and western regions experienced an upward trend. As an integrated product of mixed multi‐factor effects, runoff is regulated by temperature, precipitation, and cryospheric meltwater. Moreover, the main controlling runoff factors varied seasonally under different water source concentrations. Annually, precipitation was the main driver for runoff change in the eastern region while, correspondingly, temperature was in the western region where glaciers and the snow line boundary predominant. Besides, this study highlighted that the existing literature has significant limitations in understanding interactions among different cryospheric components and hydrologic process mechanisms when exploring the reasons for runoff variations, which needs further exploration in the future.

The additional data and code for running BRT model and generating the figures for manuscript entitled "Asynchronous warming between air and ground on the Tibetan Plateau and the drivers".

Transboundary rivers are often the cause of water-related international disputes. One example is the Amu Darya River, with a catchment area of 470 000 km(2), which passes through five countries and provides water resources for 89 million people. Intensified human activities and climate change in this region have altered hydrological processes and led to water-related conflicts and ecosystem degradation. Understanding streamflow composition and quantifying the change impacts on streamflow in the Amu Darya basin (ADB) are imperative to water resources management. Here, a degree-day glacier-melt scheme coupled offline with the Variable Infiltration Capacity hydrological model (VIC-glacier), forced by daily precipitation, maximum and minimum air temperature, and wind speed, is used to examine streamflow composition and changes during 1953-2019. Results show large differences in streamflow composition among the tributaries. There is a decrease in the snowmelt component (-260.8 m(3) s(-1)) and rainfall component (-30.1 m(3) s(-1)) at Kerki but an increase in the glacier melt component (160.0 m(3) s(-1)) during drought years. In contrast, there is an increase in the snowmelt component (378.6 m(3) s(-1)) and rainfall component (12.0 m(3) s(-1)) but a decrease in the glacier melt component (-201.8 m(3) s(-1)) during wet years. Using the VIC-glacier and climate elasticity approach, impacts of human activities and climate change on streamflow at Kerki and Kiziljar during 1956-2015 are quantified. Both methods agree and show a dominant role played by human activities in streamflow reduction, with contributions ranging 103.2%-122.1%; however, the contribution of climate change ranges from -22.1% to -3.2%.

Mountain snowpack is an important water resource in high altitude and latitude regions where terrain is typically complex. However, only limited information has been published on snowmelt pathways in such regions and their de facto contributions to streamflow and soil moisture. To fill this knowledge gap, this study integrated a snowmelt pathway tracking algorithm to the high-resolution physically based Distributed Hydrology Soil Vegetation Model (DHSVM) to track snowmelt movement and to quantify snowmelt contributions during surface hydrologic processes. A simple reservoir operation scheme was also integrated into the model. The modified model was applied to a dammed mesoscale watershed in the northeastern region of the Tibetan Plateau, China, to explore relevant snow and reservoir effects. Results show that both the annual snow contribution to soil moisture (SC-SM) and the snow contribution to streamflow (SC-S) significantly decreased between 1965 and 2019. On a monthly scale, SC-SM amplitudes were highest in the upper soil layer, while peaks in deeper layers lagged behind those in upper layers. Moreover, mean monthly SC-S from all stations revealed bimodal distributions that corresponded to the snowfall season. Finally, reservoir regulation measures only exerted minimal impacts (<= 2.0 %) on SC-S. If current climate change rates continue on the same trajectory, mountain snowpack reductions will be the primary cause for decreases in monthly and annual streamflow at the outlet of this basin. To mitigate climate change impacts, better water resource management is needed in this watershed.

Atmospheric conditions, topsoil properties and land cover conditions play essential roles in ground surface temperature (GST), surface air temperature (SAT) and their differences (GST-SAT). They determine the strength of the thermal forcing of the lower atmospheric boundary and the distributions of frozen ground in cold regions. However, the relative importance of these factors at various time scales and the underlying physical mechanisms remain less well understood. Here, we investigate the spatiotemporal patterns of GST-SAT and examine 11 potential factors in three categories in influencing the GST-SAT variations from 1983 to 2019 over the Tibetan Plateau (TP) using boosted regression tree models. The results show that the TP has experienced asynchronous warming in GST and SAT since 2001: a warming hiatus in SAT but continued warming in GST, resulting in a significantly increasing trend in GST-SAT. The relative importance of the three categories that influence the GST-SAT spatial variation was: atmospheric variables (56.1 %) > shallow soil properties (24.4 %) > interfacial land cover features (19.5 %). The importance of the factors also varied with the combinations of annual, seasonal, daily, day-time and night-time time scales, manifested by positive or negative effects. The interdecadal changes of net radiation, precipitation, wind speed and soil moisture amplified the asynchronous warming between air and shallow ground over the TP since the 2000s. These findings provide an in-depth understanding of the spatiotemporal variations of GST-SAT and the underlying mechanisms. This study will benefit the development of the Earth system models on the TP.

The Amu Darya contributed 70% of the flow to the Aral Sea in central Asia before the 1960s, when the Amu Darya streamflow to the Aral Sea started to dwindle. The severe environmental and socioeconomic disaster happened mainly due to intensified water abstraction with the backdrop of climate change. However, knowledge of up to the most recent extreme climate conditions and their changes, as well as their relations to streamflow in the basin, is still lacking. This study aims to understand extreme hydrometeorological conditions and their changes, as well as their relations in the past several decades, especially in the upper Amu Darya basin. The spatial patterns of the means of all extreme temperature indices followed the elevation gradient. The majority of the basin showed an increasing trend in extreme warm events but a decreasing trend in extreme cold events. The north of the upper basin had over 1000 mm annual precipitation, and the east had less than 300 mm annual precipitation. Overall, the upper Amu Darya basin underwent a wetting and warming annual trend. Annual streamflow in the upper subbasins was less than 750 m3 s-1, but together they produced over 1500 m3 s-1 flow in the middle reach and basin outlet. Streamflow change varied among subbasins. Correlations between climatic factors and streamflow at annual time steps were weak but distinct at monthly time steps with lagged effects. In highland subbasins with high coverage of glaciers and snow, temperature minima and maxima impacts were opposite and overwhelmed precipitation, whereas in lowland subbasins, precipita-tion was more important.

Study region: The Sanjiangyuan, located on the Tibetan Plateau, is the headwater of the three large Asia Rivers- the Yangtze, Yellow and Lancang (upper Mekong) Rivers.Study focus: Mountain glacier melt runoff, an important buffer against drought, is enhancing with climate warming. Projection of glacier (especially small glaciers) runoff change is imperative for adapting to climate change and mitigating relevant risks. We aim to provide an up-to-date knowledge of the glacier area and runoff change for 2016-2099 in the Sanjiangyuan.New hydrological insights for the region: Projections based on CMIP6 archive show that 1) glacier area in the Sanjiangyuan for the four SSPs will shrink by 36 +/- 12 % (SSP1-2.6), 42 +/- 20 % (SSP2-4.5), 49 +/- 19 % (SSP3-7.0) and 61 +/- 15 % (SSP5-8.5) by the end of the 21st century. Small glacier dominated Lancang River basin is more sensitive to climate change than large glacier abundant Yangtze River basin and Yellow River basin. The Lancang River basin is pro-jected to experience the greatest relative glacier area shrinkage, 10 % of glacier area and 55 % of glacier number will disappear for SSP5-8.5; 2) annual glacier runoff in the Yangtze River and Yellow River will reach peak water around 2080 under SSP3-7.0, while the Lancang River is already in or near peak water timing for all SSPs. Higher emission scenario tends to yield later peak water timing due to the changes in snow melt.

To better understand the hydrometeorological mean conditions and changes in Nepal, this study analyzes annual and monthly changes of mean and extreme precipitation indices for 34 stations (1986-2015) and streamflow indices for 19 stations (different available periods ranging from 1962 to 2014). The annual and monthly precipitation-streamflow relations in the major basins of Nepal are also analyzed. Nepal has heterogeneous precipitation spatial patterns in its mean and changes. The spatial pattern of extreme precipitation shows that the dry regions are prone to dry extremes and wet regions are prone to wet extremes during the past three decades. However, the annual precipitation trend is decreasing in general and the monsoon-dominated regions, namely, southern, eastern, and central Nepal, are becoming drier with less intensive precipitation while the western region is getting wetter. The trend of annual precipitation on average is decreasing at the rate of 4.2 mm yr(-1). The risk of drought is increasing in Nepal as 100% of stations show a positive trend of consecutive dry days (CDD) and the all-Nepal trend is 0.8 days yr(-1), which can put stress on the agriculture and health sector. The highest increase in CDD is at Ilam in the eastern hills with 2.9 days yr(-1). The Southeast Asian monsoon index shows a statistically significant 1-month-lagged influence on country-wise precipitation in Nepal. The effect of decreasing precipitation is seen in the streamflow trend as the majority of stations show decreasing runoff in June and July, as opposed to an increase in the winter months. CDD and maximum 1-day (Rx1day) and 5-day (Rx5day) precipitation significantly decrease with elevation.

水利枢纽工程直接影响天然河川径流情势和水生生物环境.只有兼顾人类需求和自然生态需求的水利枢纽工程才具有可持续性.以拉萨河上游旁多水利枢纽工程为例,利用变化范围法(Range of Variability Approach,RVA)和2014-2020年逐日入库天然流量、调节后的出库流量和库水位等数据,综合分析旁多水利枢纽对拉萨河径流情势的影响,定量评价径流情势各指标及整体改变程度;并结合向量统计的方法完整地展示了年极端径流时间分布特征,合理评价了水库调节对年极端流量发生时间的影响.结果表明:旁多水利枢纽工程对拉萨河径流情势影响较大,特别是对冬春季极端低流量具有持续影响;其中1月、3月、5月平均流量、年最小1天流量、年最小连续30天流量、年最小1天流量发生时间改变度为100％;水利枢纽运行期间径流情势整体改变度为62.21％,属于中度改变.虽然旁多水利枢纽对拉萨河的调节满足了农业和城镇供水需求,有利于社会和经济发展,但径流情势的中度改变,尤其是对低流量的高度改变,将对拉萨河的整个河流生态系统造成不利影响.通过对旁多水利枢纽的运行提出实时评估,指出目前水库调节存在的问题,提出水库调节应统筹兼顾社会和生态需求,为合理调度拉萨河流域水资源提供参考.

Upper Brahmaputra (UB) is the largest (similar to 240,000 km(2)) river basin of the Tibetan Plateau, where hydrological processes are highly sensitive to climate change. However, constrained by difficult access and sparse in situ observations, the variations in precipitation, glaciers, frozen ground, and vegetation across the UB basin remain largely unknown, and consequently the impacts of climate change on streamflow cannot be accurately assessed. To fill this gap, this project aims to establish a basinwide, large-scale observational network (that includes hydrometeorology, glacier, frozen ground, and vegetation observations), which helps quantify the UB runoff processes under climate-cryosphere-vegetation changes. At present, a multisphere observational network has been established throughout the catchment: 1) 12 stations with custom-built weighing automatic rain/snow meters and temperature probes to obtain elevation-dependent gradients; 2) 9 stations with soil moisture/temperature observations at four layers (10, 40, 80, 120 cm) covering Alpine meadow, grasslands, shrub, and forest to measure vegetation (biomass and vegetation types) and soil (physical properties) simultaneously; 3) 34 sets of probes to monitor frozen ground temperatures from 4,500 to 5,200 m elevation (100-m intervals), and two observation systems to monitor water and heat transfer processes in frozen ground at Xuegela (5,278 m) and Mayoumula (5,256 m) Mountains, for improved mapping of permafrost and active layer characteristics; 4) 5 sets of altimetry discharge observations along ungauged cross sections to supplement existing operational gauges; 5) high-precision glacier boundary and ice-surface elevation observations at Namunani Mountain with differential GPS, to supplement existing glacier observations for validating satellite imagery. This network provides an excellent opportunity to monitor UB catchment processes in great detail.

Understanding the effects of the snow ratio on glacier mass balance under variable climatic conditions is crucial for predicting how glaciers will respond to climate change, and for forecasting water supplies to surrounding lowland areas. Due to recent climate change, the historical annual snow ratio of the Dongkemadi (DKMD) Glacier showed a significant increasing trend (0.0538% a(-1), p < 0.05), and an abrupt upward change in 1977 due to decreasing precipitation concentration. Snow ratios with fixed precipitation concentration and nonwarming climate scenarios were calculated to isolate the impact of the snow ratio on glacier mass balance. Under nonwarming conditions, the snow ratio showed little variability, ranging from 88.4% to 99.9%. Glacier modeling results comparing five snow ratio scenarios from 1961 to 2009 showed three main features as follows. (i) Glacier mass balance was low and more sensitive to a warming climate for lower snow ratio scenarios. (ii) The difference in mass balance between the scenarios fluctuated, but generally increased with time. Spatially, the ablation area change was larger (0.4 km(2)), and the equilibrium line altitude was higher (5.9 m) in scenarios with lower snow ratios. (iii) The change in net shortwave radiation was the main reason for changes in glacial melt, and the albedo played a key role in controlling the difference of glacier energy balance between snow ratio scenarios. Rain increment only accounted for about 20%-33% of meltwater increment. Overall, this study provides valuable information to evaluate how snow ratios impact the mass balance of glaciers with ongoing climate change.