SPATIOTEMPORAL ANALYSIS AND FUTURE PROJECTIONS OF PRECIPITATION USING CMIP5 IN MAJOR CITIES OF NEPAL

Abstract

Climate change has intensified the water cycle and triggered extreme precipitation events that have increasingly affected urban areas, especially where impervious surfaces are rising due to rapid urbanization. This study investigates extreme precipitation events across ten major cities using daily data collected from DHM during 1981 to 2022. The Mann-Kendall test and Sen's slope were applied to assess the precipitation trend, while Surfer software 19.1.189 was utilized for spatial precipitation mapping based on data obtained from 32 stations. For extreme precipitation, seven extreme precipitation indices developed by ETCCD in ClimPACT version 3.1.6 were employed. Results indicate that Pokhara had the highest annual precipitation (5454.26 mm), while Dunai recorded the lowest annual precipitation (750.642 mm). Precipitation displayed an increasing trend for Kathmandu (5. 38 mm yr^{- 1}; P=0.072), Pokhara (0.33mm yr^{- 1}; P=0.965), and Gorkha (0.1mm yr^{- 1}; P=1), whereas Birgunj (-18.88 mm yr^{- 1}; P=0.005) and Illam (-11.85mm yr^-1; P=0.0013) showed a significant decreasing trend. Extreme precipitation demonstrated substantial decreases in Illam and Bhadrapur, suggesting a drying trend, while Kathmandu, Gorkha, and Pokhara exhibited increasing trends. Spatially, the average annual and monsoonal rainfall varied at the city scale. CMIP5 model projections (2024-2100) under RCP 2.6, 4.5, and 8.5 scenarios show that future precipitation will likely rise than in the past years. Extreme precipitation events have led to urban pluvial flooding in many cities, and are likely to increase more in the future.