Spatial Variations and Long-Term Trends (1901–2013) of Rainfall Across Uttarakhand Himalaya, India

Understanding spatial and temporal variations of rainfall is crucial for the ongoing and future socioeconomic and infrastructure developments in the Indian Himalayan region. However, despite such importance, the studies on rainfall distribution, variability and trends are limited and rare  in the Uttarakhand Himalayan region. To bridge the gap, this study presents an exploratory analysis of spatial distribution variations and long-term trends of annual and seasonal rainfall in Uttarakhand. At first, spatial variability is investigated, followed by long-term trend analysis using nonparametric Mann–Kendall trend test with trend-free pre-whitening (TFPW) procedure and Theil–Sen’s slope estimator. Further, dry and wet periods in Uttarakhand region and their linkages with the large-scale Southern Oscillation Index (SOI) are also explored and investigated. Annual rainfall is dominated by monsoonal rainfall (~82%), while winter rainfall contribution is only ~9%. There is a clear elevational gradient of rainfall in the winter season, but monsoon season does not feature such an elevational pattern. Mostly long-term trends of annual and monsoonal rainfall are negative, which are contributed mainly by a more evident and pronounced decline after the 1960s. Nevertheless, some areas in western and southeastern regions show positive rainfall trends. Likewise, a significant reduction in winter rainfall has been observed in Uttarakhand. Pre-monsoon rainfall experienced mostly negative trends in the central and eastern parts of the study area, while some observatories in western and southeastern indicate increasing trends. Post-monsoon rainfall trends are mostly positive, though statistically insignificant. Monsoon rainfall in Uttarakhand region is highly correlated with large-scale Southern Oscillation Index (SOI), but other seasons’ rainfall shows low correlation. These robust findings can be useful for adaptation strategies for different sectors, including agriculture and allied activities.