Future Tropical Cyclone-Induced Coastal Flood Hazards in Sofala Province, Mozambique

Abstract

This study investigates how projected changes in tropical cyclone (TC)-induced storminess, defined by extreme wind, surge, and wave events, will affect coastal flood hazards along the Sofala coastline in Mozambique under the near-future SSP5-85 climate scenario (up to year 2050). While global studies have suggested intensified storm characteristics in the Sofala region, no study to date has assessed their implications for regional coastal flood hazard in conjunction with sea-level rise (SLR). Using the synthetic STORM dataset in combination with probabilistic extreme value analysis and a storyline-based TC Idai simulation, this study quantifies the projected increase in TC-induced hazards and evaluates the relative contribution of storminess change and SLR to future flood depth and extent. Results show a consistent upward shift in the 100-year return levels for wind, surge, and wave. These changes can be mainly statistically attributed to the exceedance frequency (i.e., how often extremes occur) rather than exceedance intensity (i.e., how extreme they are when they occur). As such, the effective return period of historical 100-year events is found to be 45–60 years on average under the near-future scenario, suggesting that extreme events will become significantly more frequent. Although the upper tail dependence between surge and wave slightly weakens, the likelihood of joint surge–wave extremes still increases, lowering the joint return period from an average of 200 years to 120 years. In the TC Idai storyline, SLR accounts for 60–90% of the increase in total water levels, with a magnitude of around 0.25 m. However, storminess change contributes up to 40% in some areas, and is shown to substantially heighten flood extent and population exposure. The findings underscore the importance of integrating TC-induced storminess change in Sofala’s future coastal hazard assessments, in addition to SLR. Recommendations include extending analyses to additional synthetic TC models and emissions scenarios (e.g. SSP2-45), improving hydrodynamic model validation, and incorporating rainfall and fluvial forcing to capture the full spectrum of compound flood hazards under a changing climate.