Community-based flood damage assessment approach for lower West Rapti River basin in Nepal under the impact of climate change

The West Rapti River (WRR), one of the dynamic and economically important basins of Nepal, was focused in this study to understand the impact of climate change in localized scale. The adopted methodology was a community-based field survey followed by a hydrological modeling to estimate present and future flood damages for households and agriculture. Flood disaster occurred in 2007 was simulated and discussed. High-resolution atmospheric general circulation model's precipitation outputs for emission scenario A1B were utilized with their bias corrections to obtain the precipitation patterns over lower WRR basin for Present (1979-2003) and Future (2075-2099) periods. A conceptual hydrologic model was employed to obtain the time series of daily river runoffs for the above-mentioned time durations followed by frequency analyses for probable flood discharges of 25- and 50-year return periods. Flood inundation simulations of 50-year return period events for Present and Future were carried out with the rainfall-runoff-inundation model followed by a flood damage assessment for household and agriculture based on the inundation simulation results, and field survey data over the target area and potential flood damages were discussed. Integration of hydrological modeling and socioeconomic approach to foresee potential flood damages was achieved, and the adopted damage assessment methodology was systematically explained. The total increments of household and agriculture damages due to climate change were estimated for Present as 1.80 and 1.95, and for Future, it was 2.40 and 2.27, respectively, compared to 2007 flood disaster. Future flood frequencies, intensities, and consequent damages in the area show a significant increment compared to the present situation despite limitations and uncertainties.