COMPOUND FLOODING DRIVERS ALONG THE ATLANTIC AND GULF COASTS OF THE UNITED STATES: QUANTIFYING CHANGES AND INTERACTIONS IN TIDAL RANGE, RELATIVE SEA-LEVEL, AND EXTREME PRECIPITATION

Author

Najila Alam Porno, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2025

Degree Name

Master of Science

Department

Geography and Environmental Resources

First Advisor

Schoof, Justin

Abstract

Compound flooding caused by the influence of multiple flood drivers has emerged as one of the most pressing challenges in coastal areas of the United States. Traditional single-driver flood models often fail to capture the complexity of these events. Therefore, evaluating the impact of different factors to compound flooding is important. Given the high population density, economic significance, and low-lying topography of both the Atlantic and Gulf Coasts, a comprehensive understanding of compound flood vulnerability is vital for informed adaptation and risk mitigation. This research presents a comprehensive analysis of three key flood drivers: relative sea level, tidal range, and precipitation, across eight tide gauge stations and corresponding HUC-8 coastal watersheds (five on the Atlantic coast and three on the Gulf coast) from 1979 to 2022. The study aims to fulfill two primary objectives: (1) identify long-term trends in individual flood drivers on both annual mean and 90th percentile levels, and (2) assess the co-occurrence of the flood drivers to evaluate their potential contribution to compound flooding. Both of the objectives are evaluated on an annual and seasonal scale. Findings reveal a statistically significant and consistent increase in the relative sea level across all stations and seasons. Precipitation trends demonstrate localized intensification, particularly in the mid-Atlantic region, with seasonal peaks in winter, summer, and fall. Tidal range trends are largely insignificant, except at Galveston, TX, which shows an increasing pattern. The co-occurrence analysis indicates that fall is the most active season for joint exceedance of sea level and precipitation, likely influenced by hurricane activity, followed by winter in the Atlantic region and summer in the Gulf. These results highlight distinct spatial and seasonal hotspots of compound flood potential, emphasizing the need for region-specific and seasonally adaptive flood risk frameworks.