Understanding spatiotemporal variability in rainfall patterns is crucial for evaluating water balances needed for water resources planning and management. This paper investigates spatiotemporal variability in rainfall and assesses the frequency of daily rainfall observations from seven stations in the Kathmandu Valley, Nepal, from 1971 to 2015. Daily rainfall totals were classified into five classes, namely, A (light rain, daily rainfall < 10 mm in a day), B (moderate rain, between 10 and 50 mm), C (heavy rain, between 50 and 100 mm), D (storm, between 100 and 150 mm), and E (large storm, > 150 mm). An ordinary kriging method was used for spatial interpolation using QGIS. We performed Mann–Kendall (MK) test in conjunction with Theil-Sen’s (TS) slope estimator to detect monotonic trends, their significance, and magnitude. We find that the mountain stations depict a decreasing rainfall trend for all seasons, ranging from − 8.4 mm/year at Sankhu to − 21.8 mm/year at Thankot, whereas a mixed pattern is found on the Valley floor. Since the surrounding mountains are the chief source of surface runoff across the valley, rivers, and rivulets are substantially affected by falling rainfall tendency. Both annual rainfall amount and the number of rainy days decreased in the Kathmandu Valley over the study period. We observe a significant reduction in rainfall after 2000. As springs and shallow groundwater are the primary sources of water supply in the Kathmandu valley, it is apparent that decreasing rainfall will have (and is already having) an adverse impact on domestic, industrial, and agricultural water supplies and the livelihoods of people.

了解降雨模式的时空变异性对于评估水资源规划和管理所需的水平衡至关重要。本文研究了降雨的时空变异性，并评估了尼泊尔加德满都谷地 1971 年至 2015 年七个站点的日降雨观测频率。 日降雨总量分为五个等级，即 A（小雨，日降雨量 < 10 mm 一天）、B（中雨，10 到 50 毫米之间）、C（大雨，50 到 100 毫米之间）、D（风暴，100 到 150 毫米之间）和 E（大风暴，> 150 毫米） ）。使用 QGIS 使用普通克里金法进行空间插值。我们结合 Theil-Sen (TS) 斜率估计器进行了 Mann-Kendall (MK) 检验，以检测单调趋势、它们的显着性和幅度。我们发现山地站所有季节的降雨量都呈下降趋势，范围从 Sankhu 的 - 8.4 毫米/年到Thankot 的 - 21.8 毫米/年，而谷底则是混合模式。由于周围的山脉是整个山谷地表径流的主要来源，河流和小溪受到降雨下降趋势的显着影响。在研究期间，加德满都谷地的年降雨量和雨天数均有所减少。我们观察到 2000 年之后降雨量显着减少。由于泉水和浅层地下水是加德满都谷地供水的主要来源，很明显，降雨量减少将（并且已经）对家庭、工业和农业用水供应和人们的生计。