Pluvial Flooding Responses across Florida's Atlantic Coasts under Changing Extreme Rainfall, Land Cover, and Sea Level

This study investigated the changes in pluvial flooding scenarios for coastal urban-natural environments along the eastern coast of Florida due to changes in extreme rainfall, land cover, and sea level. Two large-scale basins, namely Florida Southeast Coasts Basin (7117 km²) and Saint Johns River Basin (31470 km²), were selected to incorporate the gradients in climate, land cover, and hydrology across the Atlantic coasts of Florida. Process-based hydrologic models were developed for these basins using U.S. Environmental Protection Agency (U.S. EPA)'s Storm Water Management Model (SWMM) 5.1. The models were calibrated and validated for 2004-2013 with observed historical streamflows. The study then evaluated significance and direction of trends in 50-year annual maximum rainfall and sea level of 1-7 day durations for 1964-2013 by non-parametric Mann-Kendall test and Theil-Sen slope estimator. Based on the results of Mann-Kendall test, stationary design rainfall and non-stationary design sea level estimations were carried out for 1-7 day durations for 2010 with varying return periods (2, 5, 10, 25, 50, and 100 year); runoff simulation for 2010 was performed accordingly. Future design rainfalls and sea levels for 2050 and 2080 were estimated based on downscaled climatic projections of 20 GCMs representing the coupled model intercomparison project (CMIP5) and the sea level rise scenarios given by the Southeast Florida Regional Climate Change Compact. Extreme runoff in 2050 and 2080 were then simulated by incorporating the future projections of design rainfalls and sea levels, and percent impervious surface from U.S. EPA. Comparative synthesis of the historical and projected future extreme runoffs suggested intensified flooding and water pollution risks across the Atlantic coast regions of Florida, including Miami in the southeast through Jacksonville in the northeast. Our findings would offer valuable insights for stormwater management and ecosystem protection for coastal built and natural environments in the southeast U.S. and across the world.