Scenario-based spatial flood hazard analysis: A case study of the Limpopo river basin

The Limpopo River Basin (LRB) is a transboundary catchment in Southern Africa, shared by South Africa, Botswana, Zimbabwe, and Mozambique. The basin is increasingly affected by climate variability, land-use change, and rapid population growth, with the Chókwe floodplain in Mozambique representing a hotspot of socio-economic vulnerability to floods. This study applies the HYPE hydrological model, driven by nine bias-corrected Regional Climate Models (RCMs), to project future high-flow extremes in the LRB under two emission scenarios (RCP 4.5 and RCP 8.5). To account for non-stationarity, flood frequency analysis was performed using the Gumbel distribution within two quasi-stationary time slices: mid-century (2030–2064) and late-century (2065–2099). Additional intensity–duration–frequency (IDF) analysis was used to evaluate changes in short-duration rainfall extremes. By the late century, ensemble projections indicate that 50-year floods will increase by ∼84 % under RCP 4.5 and ∼106 % under RCP 8.5, while 100-year floods may rise by ∼116 % and ∼142 %, respectively, compared to the historical baseline (13,551 m³/s). IDF analyses indicate an intensification of short-duration rainfall, particularly under RCP 8.5. These results suggest that floods of historically rare magnitude may recur multiple times within a century, posing increasingly significant risks to infrastructure, agriculture, and settlements in the Lower Limpopo. The findings emphasise the need for adaptive flood management, updated design standards, and strengthened transboundary cooperation in the basin. • HYPE-Limpopo model calibrated with observed data from seven gauging stations. • Nine bias-corrected CORDEX-Africa RCMs forced the simulations under RCP 4.5 and RCP 8.5. • Late-century 50-year floods may rise ∼84%, 100-year floods ∼142% under RCP 8.5. • Time-sliced Gumbel analysis shows 100-year floods may recur every 30–50 years by 2100. • Framework links ensemble projections with adaptation planning for transboundary basins.