Variability, Trends and Return Periods of Extreme Rainfall Events (EREs) over the North-Western Indian Himalayan Region (NW-IHR)

Daily gridded rainfall data from 1901 to 2020, were used to study the seasonal variation of the Extreme Rainfall Events (EREs) and Cumulative Exceedance (CumExc) at the 95th and 99th percentile thresholds in the North-Western Indian Himalayan Region (NW-IHR). The Mann–Kendall and Modified Mann–Kendall tests were used to assess the trends in EREs across seasons, besides comparing the CumExc and frequency of EREs between 1961–1990 and 1991–2020. Additionally, return periods of CumExc were estimated to predict future rainfall intensities. Among the 49 NW-IHR districts, Bandipore (J&K) reported the highest EREs (> 95th percentile) during winter and pre-monsoon, Baramulla (J&K) during post-monsoon, and Pithoragarh (UK) during monsoon. At the 99th percentile, Lahaul & Spiti (HP) recorded the most number of EREs in winter, Bandipore (J&K) in pre-monsoon, Pithoragarh (UK) in monsoon, and Baramulla (J&K) in post-monsoon. The trends of EREs indicate a substantial increase (at > 99th percentile) for all seasons in most of the region. EREs intensity between 1991–2020 is significantly higher than 1961–1990, particularly in the northern region during winter. Nevertheless, during pre- and post-monsoon seasons, most areas experienced a decline in EREs and CumExc. Estimates of CumExc suggest that UK is likely to encounter higher intensities of rainfall extremes compared to HP, J&K, and Ladakh within a 5-year and 10-year return period. This study is crucial for understanding extreme weather events in a climate change-sensitive region, providing insights into EREs frequency, trends, and return periods, which can aid in predicting flash floods and facilitating effective planning and mitigation strategies.