Urban expansion across a mountain-to-coastal gradient and its implications for hydrogeomorphic risk in Port-au-Prince, Haiti

Abstract

Rapid urban growth can intensify flood hazard when land-cover change alters runoff production on slopes and concentrates drainage toward occupied lowlands. We assessed this process in the Port-au-Prince Arrondissement, Haiti, by combining a 30 m digital elevation model and geomorphon classification with Landsat 8 land-use and land-cover maps for 2015, 2020, and 2025, a 10 m Sentinel-2 map for 2025, weighted flood-susceptibility modelling, and five daily precipitation products for 1983–2024. The 1983–2013 interval was used only to estimate the fixed R99p percentile threshold; every trend test covered 1983–2024. Landsat 8 classifications yielded overall accuracies of 98.44, 95.92, and 94.13% and Kappa coefficients of 0.9704, 0.9362, and 0.9069. Error-adjusted built-up area rose from 80.79 km 2 in 2015 to 335.43 km 2 in 2025, when it occupied 46.1% of the arrondissement, whereas vegetation decreased by 180.91 km 2 . Sentinel-2 achieved 99.35% overall accuracy and a Kappa coefficient of 0.9908. Its 17.9% built-up allocation, compared with 42.6% from Landsat 8, was interpreted as a consequence of spatial support, mixed pixels, and class redistribution rather than as direct sensor bias. Moderate and high flood susceptibility was concentrated in Tabarre, Delmas, and Cité Soleil, where low relief, flow convergence, extensive built cover, and restricted drainage coincide. Across the precipitation products, seasonal consecutive dry days increased consistently, while June–August increases in R60mm and R80mm were spatially more restricted. These findings indicate that the conversion of connected source, transfer, and receiving terrain units has increased the potential for rapid runoff delivery toward densely occupied lowlands.

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