Climate change and human activity such as reservoir operation have altered the hydrological system in the transboundary Mekong River basin (MRB) over decades, urging a need to assess the historical changes and future projections of freshwater availability. Here we examined changes of terrestrial water storage anomalies (TWSA) from the Gravity Recovery and Climate Experiment satellites in the lower MRB during 2003–2020, and subsequently partitioned and attributed them into climate-driven and non-climate-driven components using the WaterGAP hydrological model (WGHM) with and without consideration of human activities, together with a statistical method driven by climatic forcing only. Further, integrated future TWSA was projected under different climate change scenarios during 2030–2099 forced with four downscaled and bias-corrected simulations of four global climate models. Results show a decreasing TWSA trend of −3.7 ± 1.8 mm/a during 2003–2020. The WGHM-based climate-driven TWSA, which is highly correlated with the statistical modeling results, and non-climate-driven part suggests a trend of −0.3 ± 1.4 and 0.01 ± 0.07 mm/a during 2003–2016, respectively. The climate-driven TWSA is well explained by the changes in decreasing precipitation (−1.3 ± 8.5 mm/a) and increasing air temperature (0.05 ± 0.02 ℃/a) spatially and temporally, while the non-climate-driven component is closely linked to human activities such as growing sectoral human withdrawal (0.13 ± 0.14 mm/a), increasing reservoir regulation (0.01 ± 0.08 mm/a), and changing land cover. TWSA under future climate changes is projected to increase from 9.3 ± 21.4 to 12.2 ± 12.2 mm and from 1.6 ± 41.2 to 12.3 ± 30 mm in the near (2040–2059) and far future (2080–2099) under various scenarios comparing with the historical period (2003–2020). Future flood potential, estimated with TWSA and precipitation, was also projected to increase. This study provides important inferences for decision-makers and stakeholders to better understand the water cycle and manage water resources in a changing environment.

几十年来，气候变化和水库运营等人类活动改变了跨界湄公河流域 (MRB) 的水文系统，迫切需要评估淡水供应的历史变化和未来预测。在这里，我们检查了 2003 年至 2020 年期间 MRB 下部的重力恢复和气候实验卫星的陆地储水异常 (TWSA) 的变化，随后使用 WaterGAP 水文将它们划分并归因于气候驱动和非气候驱动的分量。模型（WGHM），考虑和不考虑人类活动，以及仅由气候强迫驱动的统计方法。更远，综合未来 TWSA 是在 2030-2099 年期间在不同气候变化情景下预测的，被迫对四个全球气候模型进行四个缩小和偏差校正的模拟。结果显示 2003-2020 年间 TWSA 呈下降趋势，为 -3.7 ± 1.8 mm/a。基于 WGHM 的气候驱动 TWSA 与统计建模结果高度相关，非气候驱动部分表明 2003-2016 年的趋势分别为 -0.3 ± 1.4 和 0.01 ± 0.07 mm/a。气候驱动的 TWSA 可以通过降水减少 (-1.3 ± 8.5 mm/a) 和气温上升 (0.05 ± 0.02 ℃/a) 在空间和时间上的变化很好地解释，而非气候驱动的分量则密切相关对人类活动的影响，例如增加部门性人类撤离 (0.13 ± 0.14 mm/a)，增加水库调节 (0.01 ± 0.08 mm/a)，和改变土地覆盖。与气候变化相比，未来气候变化下的 TWSA 在近期（2040-2059）和远未来（2080-2099）预计将从 9.3 ± 21.4 增加到 12.2 ± 12.2 mm，从 1.6 ± 41.2 增加到 12.3 ± 30 mm历史时期（2003-2020）。根据 TWSA 和降水估计的未来洪水潜力也预计会增加。本研究为决策者和利益相关者更好地了解水循环和管理不断变化的环境中的水资源提供了重要的推论。与 TWSA 和降水一起估计，预计也会增加。本研究为决策者和利益相关者更好地了解水循环和管理不断变化的环境中的水资源提供了重要的推论。与 TWSA 和降水一起估计，预计也会增加。本研究为决策者和利益相关者更好地了解水循环和管理不断变化的环境中的水资源提供了重要的推论。