How do CMIP6 models project changes in precipitation extremes over seasons and locations across the mid hills of Nepal?

Assessing variability of historical and projected future precipitation extremes is of high value in managing water resources effectively. The Himalayan environment of Nepal is comprised of both hills and mountains. The hills are the most susceptible to precipitation extremes and related natural hazards, which hinder the socio-economic development of the country. This study investigated the variability of extreme precipitation events over the 22 weather stations distributed across the mid hills of Nepal to identify its driving potential of extreme events. Firstly, trends and spatial distribution of different precipitation indices were computed on annual and seasonal scales for the baseline (historical) period of 1986-2015. We found that the annual maximum precipitation amount (1-day, consecutive 3-day, and 5-day) and heavy precipitation days with daily precipitation exceeding 10, 20, and 50 mm (i.e., R10, R20, and R50 respectively) show dominantly falling trends during the historical period. Noticeably, while analyzing at a seasonal scale, we found that the precipitation amount exhibited a statistically significant decreasing pattern during the monsoon season. This study then assessed possible changes of those indices under future climatic conditions using the latest set of scenarios from ten CMIP6 (Coupled Model Inter-comparison Project phase 6) models dataset for the near future period (2021-2050) under two shared socio-economic pathways (SSP245 and SSP585). The projection showed a wider range of deviation with respect to the baseline, predominantly increasing heavy precipitation. Overall, the increasing pattern of the intensity, duration, and frequency of extreme events indicates the region would possess more risks of natural hazards such as floods, landslides, and soil erosion in the future. Furthermore, most of the climate models showed that consecutive dry days (CDDs) are projected to increase, which could significantly impact agriculture facilities, food security, and water scarcity and ultimately could increase the vulnerability of hill communities. Our findings are expected to help understand the extremities of precipitation variability and have strong policy implications indicating that adaptation measures that can reduce risks make society less vulnerable and more resilient to extremes.