Melamchi Extreme Flood in Response to Climate Change in the Central Himalaya of Nepal

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Climate change induced extreme precipitation and the associated rise in temperature have led to catastrophic floods. A flood occurred in the Melamchi River on 15 June and recurred on 31st July, 2021 in Nepal. This study has investigated these extreme flood events and their close nexus with climate. The available daily and hourly precipitation, temperature, snow depth and discharge data were analyzed. The regional flow during both flood events were estimated using 1-D hydraulic HEC-HMS model and the correlation among rainfall to the runoff and temperature with snow water equivalent were examined. The snow water equivalent was converted to the stream flow of the river. Result show that the Melamchi region found an average annual rainfall of 2610mm during 1992–2021. Specifically, Shermathang and Tarkeghang has observed the highest daily average rainfall of 26.8mm and 39.2mm during the first and 61.4mm and 66.6mm during the second flood event, respectively. The discharge found at the Melamchi Bazar was at 2893m3 /s and 1105 m3 /s in the first and second events respectively in which Kiwil, Chanaute and Melamchi were highly contributed. The peak 10m interval flood discharge during the second event at Nakote was found 285 m3 /s. The daily average discharge of Bhemathang was 357m3 /s and 76m3 /s on both events, respectively. The rainfall and runoff at the Nakote station are poorly correlated while snow water equivalent and temperature showed positive correlation during summer which indicates melting of the snow. In response to summer temperature increased, SWE and snow depth were decreased by melting. The snowmelt contribution to discharge was found 9.68m3 /s in the Melamchi River during the Summer season. The daily average snow water equivalent of the upper basin was found 672 mm which are very potential to melt out in response to increased temperature. The finding showed that precipitation is the main climatic driver while temporary damming and increasing temperature also contributes to the timing and magnitude of the of the Melamchi flood.

Binod Baniya, Qiuhong Tang, Tirtha Raj Adhikari, Gang Zhao, Gebremedhin Gebremeskel Haile, Madan Sigdel and Li He