Numerous endorheic lakes in the Qinghai-Tibet Plateau (QTP) have shown a dramatic increase in total area since 1996. These expanding lakes are mainly located in the interior regions of the QTP, where permafrost is widely distributed. Despite significant permafrost degradation due to global warming, the impact of permafrost thawing on lake evolution in QTP has been underexplored. This study investigated the permafrost degradation and its correlation with lake area increase by selecting four lake basins (Selin Co, Nam Co, Zhari Namco, and Dangqiong Co) in QTP for analysis. Fluid-heat-ice coupled numerical models were conducted on the aquifer cross-sections in these four lake basins, to simulate permafrost thawing driven by rising surface temperatures, and calculate the subsequent changes in groundwater discharge into the lakes. The contribution of these changes to lake storage, which is proportional to lake area, was investigated. Numerical simulation indicates that from 1982 to 2011, permafrost degradation remained consistent across the four basins. During this period, the active layer thickness first increased, then decreased, and partially transformed into talik, with depths reaching up to 25 m. By 2011, groundwater discharge had significantly risen, exceeding 2.9 times the initial discharge in 1988 across all basins. This increased discharge now constitutes up to 17.67 % of the total lake water inflow (Selin Co). The dynamic lake water budget further suggests that groundwater contributed significantly to lake area expansion, particularly since 2000. These findings highlight the importance of considering permafrost thawing as a crucial factor in understanding the dynamics of lake systems in the QTP in the context of climate change.

Identifying the changes in terrestrial water storage is essential for a comprehensive understanding of the regional hydrological mass balance under global climate change. This study used a partial least square regression model to fill the observation gaps between GRACE and GRACE-FO and obtained a complete series of terrestrial water storage anomaly data from April 2002 to December 2020 from southeast China. We investigated the variations in terrestrial water storage anomalies in the region and the influencing factors. The study revealed that terrestrial water storage (TWS) anomalies have been increasing in the region, with an average increase of 0.33 cm/yr (p < 0.01). The intra-annual variation showed a positive anomaly from March to September and a negative anomaly in other months. Terrestrial water storage anomalies increased in most regions (especially in the central and northern parts), whereas they decreased in the southern parts. In terms of the components, the soil moisture storage (SMS) contributes 58.3 % and the surface water storage (SWS, especially reservoirs water storage) contributes 41.4 % to the TWS. The study also found that changes in the precipitation explain approximately 71.7 % of the terrestrial water storage variation, and reservoirs contributes to the remaining 28.3 %. These results are essential for understanding the changes in the hydrological cycle and developing strategies for water management in Southeast China.

Study region: The Northwest inland basins of China (NWC).Study focus: Terrestrial water resources, especially groundwater resources, are the main source of water for human activities and for maintaining the stability of the ecological environment in NWC. Excessive consumption of water resources will seriously affect the sustainable utilization of water resources and ecological security in this region. Therefore, it is urgent to clarify the long-term changes in water storage in this area in order to handle the pressure of future water re-sources and the natural environment. Using GRACE satellite datasets and global hydrological models (GHMs) products, this study analyzed spatiotemporal variations in terrestrial water storage anomalies (TWSA), groundwater storage anomalies (GWSA), soil moisture, snow water equivalent, and canopy interception combined anomalies (SSCA) in NWC through the application of the water balance, trend decomposition, and empirical orthogonal decomposition methods. Furthermore, the driving factors of water storage change and feasible water resource manage-ment strategies were discussed. New hydrological insights for the region: TWSA in the NWC has experienced a continuous decline over the past nearly 40 years, while SSCA has shown a weak increasing trend (0.03 cm yr-1). Since the availability of glacial retreat data (2003-2016), glacial water storage in the NWC has decreased by 0.09 cm per year, while TWSA, SSCA, and GWSA have changed at rates of -0.25, 0.02, and -0.18 cm yr-1, respectively. The North Tianshan Rivers Basin has become one of the areas with the most severe groundwater depletion in China. 2005-2010 was a turning period in the changes of TWSA, followed by widespread water loss across the NWC. Glacier and snow melt are the most important factors for the decline of TWSA in the Tianshan mountains area, and over -exploitation of groundwater by human activities is a secondary factor. For other regions, Groundwater losses remain the most significant contributor to TWSA losses. The massive loss of water storage in the Tianshan Mountains area, especially the accelerated retreat of glaciers, will affect the stable water supply to the middle and lower reaches of the oasis region, perhaps leading to increased groundwater extraction, which will threaten regional water security and sustainable development. Developing a water-saving society and implementing inter-basin water transfer arefeasible ways to alleviate the water resource crisis. Conducting a comprehensive analysis of all inland rivers in China helps to facilitate horizontal comparisons between various basins, thereby providing more comprehensive insights of water storage fluctuations. The data on water storage changes, extending back to 1980, provide a longer-term perspective on water resource changes in the region, which can contribute to enhancing water resource security and ecological environ-mental protection.

Despite that the supplying role of cryosphere (glaciers, permafrost, and snow) in groundwater storage (GWS) in Tibetan Plateau (TP) is well-known by comparing their long-term linear trends, the question whether GWS could in turn affect the variation of cryospheric variables remains controversial, since long-term trend analysis fails to distinguish the direction of their interplay. To find evidence of GWS causally affecting cryosphere, this research resorts to the causal inference community and investigates a novel causal interaction between GWS and cryosphere in TP: nonlinear dynamic causality (NDC), based on the Nonlinear Dynamic System (NDS) theory. The specific method applied is called Convergent Cross-mapping (CCM), which detects NDC between two targeted variables X and Y from both directions (X & RARR; Y, Y & RARR; X). Important findings are summarized as follows: (1) With CCM, NDCs with similar strengths are found from glaciers retreat, snowmelt, and permafrost thaw to GWS, respectively; (2) Also in the form of NDC, GWS is proven to reversely affect permafrost, but not to glacier and snow; (3) NDCs are also found between GWS and other hydrometeorological variables in TP, including lakes, soil moisture, precipitation, and temperature; (4) Some nontraditional NDCs from glaciers and lakes towards GWS are identified. Overall, using CCM, our new findings about NDC answer the controversial question of whether GWS could in turn affect cryosphere, completing previous conclusions about how GWS interplays with cryosphere in TP, and more importantly, this research would shed light on future causality detection in hydrology.

Understanding terrestrial water storage (TWS) dynamics and associated drivers (e.g., climate variability, vegetation change, and human activities) across climate zones is essential for designing water resources management strategies in a changing environment. This study estimated TWS anomalies (TWSAs) based on the corrected Gravity Recovery and Climate Experiment (GRACE) gravity satellite data and derived driving factors for 214 watersheds across six climate zones in China. We evaluated the long-term trends and stationarities of TWSAs from 2004 to 2014 using the Mann-Kendall trend test and Augmented Dickey-Fuller stationarity test, respectively, and identified the key driving factors for TWSAs using the partial correlation analysis. The results indicated that increased TWSAs were observed in watersheds in tropical and subtropical climate zones, while decreased TWSAs were found in alpine and warm temperate watersheds. For tropical watersheds, increases in TWS were caused by increasing water conservation capacity as a result of large-scale plantations and the implementation of natural forest protection programs. For subtropical watersheds, TWS increments were driven by increasing precipitation and forestation. The decreasing tendency in TWS in warm temperate watersheds was related to intensive human activities. In the cold temperate zone, increased precipitation and soil moisture resulting from accelerated and advanced melting of frozen soils outweigh the above-ground evapotranspiration losses, which consequently led to the upward tendency in TWS in some watersheds (e.g., Xiaoxing'anling mountains). In the alpine climate zone, significant declines in TWS were caused by declined precipitation and soil moisture and increased evapotranspiration and glacier retreats due to global warming, as well as increased agriculture activities. These findings can provide critical scientific evidence and guidance for policymakers to design adaptive strategies and plans for watershed-scale water resources and forest management in different climate zones.

Understanding how groundwater storage (GWS) responds to climate change is essential for water resources management and future water availability in the Tibetan Plateau (TP). However, the dominant factor controlling long-term GWS changes remains unclear and its responses to climate change are not well understood. Here we combined multi-source datasets including in-situ measurements, satellite observations, global models, and reanalysis products to reveal that GWS increased at 5.59 +/- 1.44 Gt/yr during 2003-2016 while showing spatial heterogeneities with increasing trends in northern TP and glacial regions and declining trends in central and southern TP. The accelerated transformation from solid water (glaciers, snow, and permafrost; -17.72 +/- 1.53 Gt/yr) into liquid water provide more recharge to groundwater, dominating the total GWS increase. This study contributes to a better understanding of the hydrological cycle under climate change and provides key information for projecting water availability under different future scenarios in the TP.

Terrestrial water storage (TWS) in the endorheic Tibetan Plateau (ETP) increased from 2002 to 2012 but decreased in 2012-2016. This study used Gravity Recovery and Climate Experiment (GRACE) data and Global Land Data Assimilation System (GLDAS) data to analyse TWS changes in the ETP in 2012 from increasing to decreasing. The results showed that these TWS changes could be divided into two stages. From April 2002 to August 2012, TWS increased at a rate of 4.43 Gt/yr from the GRACE-Mascons and 1.11 Gt/yr from the GRACE-SH, whereas after September 2012, it declined at a rate of-5.62 Gt/yr from the GRACE-Mascons and-6.99 Gt/yr from the GRACE-SH. The increase in lake water storage (LWS) (7.98 Gt/yr) was higher than the loss of other components from 2002 to 2012, therefore, the LWS gradually dominated the increase in TWS. However, the soil moisture storage (SMS) decreased more significantly (-5.27 Gt/yr) than the increase in LWS (<1 Gt/yr) during 2012-2016, accounting for 66% of the decrease in TWS in the ETP. From a water balance perspective, the relationship between precipitation (P) and evapotranspiration determined the region's changes in TWS. It was found that 90% of the decrease in TWS in the ETP during 2012-2016 was attributed to an increase in potential evapotranspiration (PET), whereas 7% was attributed to a decrease in P. Thus, climate change (P and PET) accounted for 97% of the TWS reduction during 2012-2016. Furthermore, 3% of the decrease in TWS in the region was attributed to land surface changes.

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.

The northeastern Tibetan Plateau (NETP), bordering the endorheic lake basins and the Upper Yellow River region, has been disturbed by increasing human activities in recent years. The NETP water storage changes could be a combined effect of climate variability/change and human activities (e.g., reservoir operation). However, whether the human activities have evidently altered hydrological processes and become key drivers of total terrestrial water storage (TWS) changes in the NETP remains unclear. To explore the roles of human interventions in changing surface water storage (SWS) and thus influencing regional TWS changes in the NETP, in comparison with natural drivers, this study quantitatively disaggregated and compared the contributions of TWS changes from climate-dominated natural lakes and man-regulated reservoirs at different timescales. Time series of Gravity Recovery and Climate Experiment (GRACE) TWS anomalies (TWSA) exhibited an overall upward trend (0.78 +/- 0.06 Gt/yr, p < 0.01) with evident periodic fluctuations from April 2002 to August 2020. Although the GRACE TWSA was more substantially influenced by changes in natural lake water storage (0.96 +/- 0.02 Gt/ yr) rather than reservoirs (0.54 +/- 0.04 Gt/yr) in the long-term trend, the man-regulated reservoir water storage changes can significantly dominate the GRACE TWSA on interannual and intra-annual timescales, especially in the second sub-period (2013.01-2017.06; GRACE TWSA change rate:-1.82 +/- 0.29 Gt/yr, p < 0.01, in comparison with the change rate of reservoir water storage of-1.28 +/- 0.17 Gt/yr, and the natural lakes of 0.72 +/- 0.07 Gt/yr). In some abnormal years, the reservoir storage changes were even close to the overall signal of region-wide GRACE TWSA. In addition, the increase in soil moisture storage (long-term linear trend: 0.65 +/- 0.06 Gt/yr, p < 0.01) was also a key factor that cannot be neglected. Our results suggest that human activities are becoming one of the key factors influencing TWS changes in the NETP.

Vegetation is affected by hydrological cycle components that have altered under the influence of climate change. Therefore, it is necessary to investigate the impact of hydrological cycle components on regional vegetation growth, especially in alpine regions. In this study, we employed multiple satellite observations to comprehensively investigate the spatial heterogeneity of hydrological cycle components in the Yarlung Zangbo River (YZR) basin for the period 1982-2014 and to determine the underlying mechanisms driving regional vegetation growth. Results showed that the normalized difference vegetation index (NDVI) values during May-October were high, and the NDVI values increased from the upper reaches of the YZR to its lower reaches, reflecting the enhancement of vegetation growth. Annual precipitation, precipitation-actual evapotranspiration (AET), and snow water equivalent (SWE) all affect terrestrial water storage in the YZR basin through changes in soil moisture (SM), i.e., SM is the intermediate variable. Seasonal variability of vegetation is controlled mainly by precipitation, temperature, AET, SM anomaly, and SWE. Groundwater storage anomalies (GWA) and terrestrial water storage anomalies (TWSA) were not reliable indicators of vegetation growth in the YZR basin and the midstream and downstream regions. The effects of GWA and TWSA on vegetation occurred in the upstream region.