ABSTRACT
The Himalayan region is experiencing rapid change in intensity of rainfall and increases and decreases in temperature. This study analyzes the climate projections of climate variables projected from the latest Coupled Model Intercomparison Project (CMIP6) models for three different physiographic regions (low-lying plain areas, the middle mountains, and the high Himalayas) of the Koshi River Basin (KRB), Nepal. This study investigated the variability of rainfall and temperature in four seasons over the 38 weather stations distributed across the low-lying plain areas, middle mountains, and High Himalayas region of the KRB. First, we use the data sets of the BCC, CANESM-CCCma, CNRMCM-CERFACS, and IPSL. The quantile mapping method was employed to correct bias in the GCM data for the near-future (2021-2045), mid-future (2046-2076), and far-future periods (2077-2100) under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5). The results described the change of climate variables in regional and seasonal scales. The future climate projection showed a wide range of deviation and predominantly increasing heavy rainfall in the middle mountains and High Himalayan region. The monsoon rainfall for the low-lying plain region is expected to increase by more than 10% for near-future and mid-future periods, whereas for the middle mountains and the high Himalayas region, the monsoon rainfall is expected to increase by 20% for mid-future and far-future periods. Similarly, the basin expects to experience warming across all three regions for all future periods. Significantly, the high Himalayas region expects to experience an increase in temperature by 1.5-5°C in coming future periods. Overall, the increasing rainfall pattern indicates the risk of extreme events like floods, flash floods, landslides, and soil erosion in the future. The reported changes in rainfall and temperature will help understand the extremities of climate variability of the KRB and assist in providing policy implications and adaptation measures against natural hazards.
