On the solid and liquid precipitation characteristics over the North-West Himalayan region around the turn of the century

In the backdrop of widely reported global warming, the present study focuses on the solid and liquid precipitation dynamics over the North-West Himalayan (NWH) region around the beginning of the twenty-first century. Using 40 years long, high resolution (0.25° × 0.25°) fifth generation of ECMWF atmospheric reanalyses of the global climate (ERA-5) data sets for precipitation and several atmospheric variables, we assess the changes in the annual cycle of solid and liquid precipitation characteristics in the last two decades (L20 years—2000–2019) as compared to the first two decades (F20 years—1980–1999). Validation of the ERA-5 data set has been carried out against the ground-based observations of rainfall and mean temperature prepared by India Meteorological Department (IMD). A good match of ERA-5 monthly rainfall with the IMD data set (correlation = 0.69) is noted over the NWH region over the last 40 years. The statistically robust K–S test suggests a remarkable variation in the distribution of most of the atmospheric variables across the NWH region at a 95% confidence level in the L20 years as compared to the F20 years. Further to this, a significant reduction in the precipitation during the pre-monsoon (MAM) season is noted across the NWH region (at 5% significance level), these observed changes are found to be well corroborated with the changes observed in the atmospheric circulation (weak winds) and enhanced temperature. For the JJAS rainfall, only parts of Uttarakhand witnessed significant enhancement of rainfall (specifically the Pithoragarh region), and notable increasing trend for both the mean and standard deviation of precipitation suggests an increase in extreme events in recent years. The peak snowfall month has experienced an early shift in the L20 years in comparison to the F20years (March–February) and an overall decrease in the snowfall amount has also been recorded in the annual cycle in association with the elevation of the region. Secular changes noted in the longitudinal and latitudinal cross-section of hydrometeors (snow and liquid water concentrations), specific humidity, and atmospheric circulation appear to be the plausible reasons for the noteworthy changes in the precipitation dynamics over the NWH region.