Climate change induced Melamchi extreme flood and environment implication in central Himalaya of Nepal

Flood occurred in the Melamchi River on June 15 and recurred on July 31, 2021 have led notorious impacts in Nepal. This study has investigated these extreme flood events and their nexus with climate i.e. precipitation and temperature. The available daily and hourly hydro-meteorological data were analyzed. The regional flow during both flood events were estimated using 1-D hydraulic HEC-HMS model and the correlation among rainfall -runoff, temperature with snow water equivalent were examined. Result show that the Melamchi region found an average annual rainfall of 2610 mm during 1992–2021. Specifically, the middle section i.e. Shermathang and Tarkeghang has observed the highest daily average rainfall of 26.8 mm and 39.2 mm during the first and 61.4 mm and 66.6 mm during the second flood event, respectively. The discharge found at the Melamchi town segment was at 2893 m3/s and 1105 m3/s in the first and second events respectively in which regional contribution into discharge were found significant. The Bhemathang, which is landslide damming area where The daily average discharge observed 357 m3/s and 76 m3/s on both events, respectively. At the Nakote, the rainfall and runoff are poorly correlated while snow water equivalent and temperature showed positive correlation during summer. The snowmelt contribution to discharge was found 9.68 m3/s in the Melamchi River during the Summer season. The regional contribution to discharge and spatial variations of precipitation during flooding events showed that precipitation is the main climatic driver while temporary damming and increasing temperature also contributes to the magnitude of the Melamchi flood.