Flood Vulnerability under High-Warming Scenarios: Insights from flood wave Projections and Socio-Economic Assessment

Climate change intensifies the global hydrological cycle, altering hydrometeorological variables and amplifying flood risks, with significant social, economic, and environmental consequences. Reliable flood estimates are crucial for designing cost-effective flood protection structures. The assessment often focusses only on peak discharge, overlooking vital factors like flood wave frequency, duration, and time to peak, which are key elements for preparedness and resilience. Although. the use of general circulation models (GCMs) for future simulations has advanced our understanding of catastrophic floods under climate change. Yet, the socio-economic impacts of these events remain insufficiently explored, leaving crucial vulnerabilities inadequately addressed. This study therefore evaluates the flood characteristics and socio-economic vulnerabilities in a large river basin using downscaled GCMs of CMIP6. The hydrological and hydrodynamic models were used for determining the flood wave characteristics considering non stationarity. We also examine the benefits of limiting global warming to 1.5°C, aligned with COP28 goals, by assessing global warming levels of 1.5°C, 2°C, and 3°C and the EF (2021–2050) and FF (2071–2100).

The flood peaks in major cities are projected to rise by 10–14% during pre-monsoon and monsoon seasons, with high-warming scenarios causing a ~35% increase in high flow by 2100. However, limiting the warming to 1.5°C could reduce the return flood discharge by 9,000 m³/s in FF. The projections indicate a paradigm shift in the flood wave characteristics of the basin, with a notable increase in both flood wave duration (~0.31 days per year) and frequency (~3 more flood waves) during the pre-monsoon and monsoon seasons. Socio-economic vulnerability assessments reveal heightened risks under high-warming scenarios, driven by population growth and intensified hydroclimatic extremes, leading to greater inundation extents, depths, and displacement risks. These findings underscore the urgent need for global and regional cooperation, evidence-based policies, and climate-resilient infrastructure to mitigate flood risks and adapt to evolving hydroclimatic extremes in vulnerable transboundary basins.