In recent decades, the hydrological balance/budget over Himalayan river basins has imperatively become crucial for decision-making in flood risk, water resource management, identifying water-sensitive areas etc. In the present study, assessment of the abating total water storage (TWS) in the three river basins viz. Indus (IRB), Ganga (GRB) and Brahmaputra (BRB) is carried out. TWS contributory factors, viz. precipitation, evaporation, runoff, snow water equivalent (SWE), soil moisture, groundwater etc., are arguably assessed. TWS anomaly and other variables are considered, and corresponding statistical seasonal (winter, premonsoon, monsoon and postmonsoon) trends are calculated using the Mann–Kendall test and the Theil-Sen estimator. Dominant monsoon precipitation over GRB and BRB and winter precipitation over IRB contribute to the replenishment of TWS with almost a month lag. Still, there are decreasing TWS trends. Most of the basins are drying, though slower during monsoon. Maximum decrease in TWS is observed in postmonsoon over IRB, while GRB and BRB show it in premonsoon. The highest intraseasonal variability is shown by precipitation, followed by runoff. Evaporation shows less variability and is less dependent. Present work will be of utmost importance for the policy or planning for governance at the state level for societal benefit.

近几十年来，喜马拉雅河流域的水文平衡/预算对于洪水风险、水资源管理、确定水敏感区域等决策至关重要。在本研究中，评估总水储量减少（TWS） ）在三个河流域即。进行印度河（IRB）、恒河（GRB）和雅鲁藏布江（BRB）。 TWS 的影响因素，即。可以评估降水、蒸发、径流、雪水当量（SWE）、土壤湿度、地下水等。考虑 TWS 异常和其他变量，并使用 Mann-Kendall 检验和 Theil-Sen 估计量计算相应的统计季节性（冬季、季风前、季风和季风后）趋势。 GRB和BRB的主导季风降水以及IRB的冬季降水对TWS的补充贡献了近一个月的滞后。尽管如此，TWS 的趋势仍呈下降趋势。大多数盆地正在干燥，但在季风期间干燥速度较慢。 TWS 的最大减少出现在 IRB 的季风后，而 GRB 和 BRB 则出现在季风前。最高的季节内变化表现为降水，其次是径流。蒸发显示出较小的变异性并且依赖性较小。目前的工作对于国家层面的社会效益治理政策或规划至关重要。