Unfolding extreme rainfall events characteristics over the North-West Himalayan region based on recent GPM-IMERGV7 remotely sensed observations

Abstract

Extreme Rainfall Events (EREs) over the North West Himalayan (NWH) region of India have been examined for the monsoon season using the latest IMERG V07B rainfall data of 0.1°x0.1° resolution for recent two decades (2000–2022). A strong correlation of 0.95 was noted between IMERG and ground-based IMD data. Intensity corresponding to the EREs for the 95th, 98th, 99th, 99.5th, and 99.99th percentile is found to be 17.43 mm day⁻¹, 34.47 mm day⁻¹, 50.52 mm day⁻¹, 68.66 mm day⁻¹, and 197.75 mm day⁻¹ respectively. In all the classes of intensity, the magnitude is highest along the southwest foothills (1000 m – 3000 m) of NWH with the highest intensity over Dharamshala and Mandi regions (HP) along with southeast region of UK. Statistically robust Mann-Kendall (MK) test revealed a significant decreasing trend (95 % confidence level) in rainfall intensity corresponding to the 99th percentile and above over Dharamshala and Mandi. A late arrival of the 1-day maxima rainfall is observed in Dehradun, Mandi, and Leh regions whereas a contrasting behaviour is unveiled over Pithoragarh, Munsiyari, and Chamoli regions. For the NWH region as a whole, both frequency and intensity are significantly decreasing for the 99.99th percentile, though Ladakh region witnesses a significant increasing trend in frequency and intensity for all the categories barring the 95th percentile. An elevation-wise study of the distribution of frequency and intensity of EREs highlights two major breakpoints (∼ 850–1000 m and ∼ 3500–4000 m). The highest percentage of EREs (except 99.99th percentile) are concentrated within 1000 m – 2000 m (< 1000 m). The study revealed that intense EREs of magnitude 300 mm day⁻¹ have the shortest revisit period of 30–45 years in Dharamshala and Mandi. The present study would prove to be useful for policymakers for mitigation strategy and infrastructure development planning in mountainous regions of India and provide a framework for analyzing EREs across the global mountain regions.