Spatio-temporal variability of extreme precipitation in Nepal

Nepal is one of the most vulnerable countries to climate change impacts. Extreme weather events associated with heavy precipitations are the principal causes of landslides, debris flows and all types of floods disasters in the country, which by causing tremendous losses of life and property affects the socio-economic development. Given the limited availability of knowledge in spatio-temporal distribution of precipitation in Nepal, this study analyses the spatial distribution of monthly and annual precipitation and 1-day extreme precipitation and their trends utilizing a large number of stations (291 stations for the first time) distributed across the country for the period of 1966-2015. This study focuses on the exploration of elevational dependencies of precipitation to demonstrate the effect of topographic heterogeneity caused by the numbers of broad and narrow river valleys and mountain slopes and ridges. Also, this study investigates the relation of 1-day extreme precipitation with mean annual precipitation. Our results show the peak annual precipitation elevation between 2,000 and 3,500m above sea level, while in contrast 1-day extreme precipitation peaks are found at lower elevation in the southern foothills with its highest intensity in a central region of the country. The occurrence of 10% of mean annual precipitation in a single day has been observed in 75% of the analysed stations which in turn indicates the high likelihoods of initiation of landslides, soil erosions and floods in different parts of the country. There is no definitive countrywide decadal trend in extreme precipitation intensity and occurrence. A station-wise trend clearly shows the increase in extreme precipitation events in western mountainous regions in the recent decades. In other locations, the mixed patterns of station-wise increasing and decreasing trends are found.