Dynamics of Meteorological and Agricultural Drought in the Karnali River Basin, Nepal

Drought poses significant threats to the Himalayan region, but comprehensive assessments incorporating meteorological, agricultural, and ecological dimensions are scarce. This work uses 30 years of observational and satellite data to provide a multidimensional drought analysis for the Karnali River Basin in western Nepal based on ground station precipitation records, reanalysis data, and satellite vegetation index (NDVI). Principal component analysis was used to develop composite meteorological and agricultural drought indices for an assessment of drought propagation across domains. Averaged over the basin, results reveal a persistent long-term greening trend (+12% in NDVI over 25 years), which contrasts with a slight but significant increase (0.031/yr) in long-term meteorological drought severity (SPI12) and a non-significant declining tendency in soil moisture (−0.0024/yr). Mountainous regions were hotspots, with drought frequency surpassing 12%, whereas the Terai lowlands were more resilient. Vegetation responses lagged soil moisture anomalies by about a month. The composite indices were moderately correlated (r = 0.55). They revealed that meteorological droughts were very volatile (52% normal conditions), while agricultural drought evolved more slowly with greater permanence (64% normal conditions). These results highlight dimensions of growing drought threats in this basin and suggest that the development of integrated drought surveillance frameworks is a key to early warning systems, agricultural planning, and adaptive water resource management of mountain regions in the world under a changing climate.