Evaluation of climate change impact on future flood in the Bagmati river basin, Nepal using CMIP6 climate projections and HEC-RAS modeling

Abstract

The unpredictability of hydrological patterns attributed to climate change has led to significant alterations in weather patterns, precipitation irregularities, and temperature extremes. These changes have resulted in natural calamities, prompting an examination of the impact of climate change on evolving flood patterns. This study investigates the potential effects of projected future precipitation in the Bagmati River Basin, Nepal, on flood inundation extent during three different time periods in this century. Two General Circulation Models (GCMs) climate scenarios under the Coupled Model Inter-comparison Project Phase 6 (CMIP 6) framework were employed to project future conditions. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) was utilized to simulate flood events and generate maps for these climate scenarios. The findings suggest that i) precipitation levels are anticipated to increase in both models under the Shared Socioeconomic Pathways (SSP) 2–4.5 and 5–8.5 scenarios, with the most pronounced increase projected between 2071 and 2100 under the EC-EARTH3 SSP5-8.5 scenario, indicating a 120% rise from the reference period, and ii) flood inundation areas are expected to expand relative to the simulated reference period, with the most extreme scenario under SSP5-8.5 forecasting potential inundation of 359 km² and 342 km² in the ACCESS-CM2 and EC-EARTH3 models, respectively. By examining these future scenarios, this study aims to enhance the understanding of the long-term impacts of climate change on flooding events and support the development of effective strategies for mitigation and adaptation. These findings are crucial for policymakers, urban planners, and disaster management professionals to prepare for and address the challenges posed by climate-induced flooding in the coming decades.