Source: Geophysical Research Letters
Coastal cities are at increasing risk of compound flooding events, such as when heavy rainfall and storm surges occur simultaneously during hurricanes. However, the processes that contribute to urban compound flooding aren’t well understood at smaller scales.
To better understand how different drivers of flooding interact near coastal cities, Xu et al. used the Energy Exascale Earth System Model (E3SM) with the River Dynamical Core (RDycore) shallow-water equation library built to simulate extreme flooding events. Their modeling highlights the importance of rural runoff for urban flooding events, the researchers say, while also underlining the continued role of coastal wetlands in blunting the dangers of compound flooding events.
The authors simulated 2011’s Hurricane Irene in the Delaware River basin. Using the kilometer-scale E3SM configuration allowed them to simulate flood dynamics at the building scale in many cases. They looked to see how factors such as runoff sources, interactions between rainfall and storm surge, and sea level rise affected flooding in urban areas near the coast. The biggest factor in severe flooding was topography, the authors say, especially in surrounding rural areas, where topographic features can funnel water toward cities. Features like the elevation change between outlying and urban areas and the connectivity of drainage systems had a significant effect on the severity of urban flooding.
Storm surges are predicted to become worse as sea levels rise, intensifying compound flooding. In their model, the authors re-created this effect but noted that most of the expanded flooding under sea level rise occurred in coastal wetlands, which acted to absorb much of the surge. This result is an indication of how valuable these ecosystems are for nearby urban areas, the authors say. (Geophysical Research Letters, https://doi.org/10.1029/2026GL122550, 2026)
—Nathaniel Scharping (@nathanielscharp), Science Writer
