Characterizing the hydrometeorology of 2021 Melamchi landslide dam-break flood

Accurate prediction of landslides in the Himalayan region is challenging. Landslides often trigger cascading hazards ranging from debris flow, landslide dam outburst floods, and critical infrastructure failure. Here we discuss the hydrology and hydrometeorology of the June 2021 Melamchi flood. This event caused extensive damage to downstream settlements and impacted several infrastructures, including the nations largest Melamchi Drinking Water Supply System. There are few pieces of evidence that apprise the massive flood/ debris flow struck due to the outburst of upstream landslide damming lake. We integrate the meteorological, hydrological, and hydraulic information to characterize the cascading impacts of the Melamchi flood. We develop a hydrological-hydrodynamic model to replicate and diagnose the flood dynamics. We i) discuss the potential drivers of the Melamchi flood, ii) highlight the need for an integrated modeling framework to advance fundamental understanding of cascading hazards, and iii) emphasize the urgency to improve capabilities for hazard predictions and early warning systems.