It is well understood that natural disasters interact to affect the resilience and prosperity of communities and disproportionately affect low income families and communities of color. However, given the lack of a common theoretical framework, it is rare for these interactions to be well understood or quantified. As an example, we consider the interaction of severe weather events (e.g., hurricanes and tornadoes) and epidemics (e.g., COVID-19). Observing events unfolding in southeastern U.S. communities has caused us to conjecture that the interactive effects of catastrophic disturbances and stressors might be much more considerable than previously recognized. For instance, hurricane evacuations increase human aggregation, a key factor that affects the transmission of acute respiratory infections like SARS-CoV-2. Similarly, weather damage to health infrastructure could significantly reduce a community’s ability to provide services to people sick with COVID-19 and other diseases. As globalization and human population and movement continue to increase and weather events due to climate change are becoming more intense and severe, such complex interactions are expected to magnify and significantly impact environmental and human health.

Tropical coastal communities accommodate critical infrastructure, densely-populated urban regions, tourism-driven economies, and industrial facilities. These communities are prone to multiple flood hazards such as nuisance flooding, tropical cyclones, extreme rainfall events, and sea-level rise (SLR). Thus, governments and stakeholders Are pursuing a range of measures to enhance flood resiliency. These alternatives can be classified into structural (i.e., conventional infrastructure), non-structural, natural and nature-based features (NNBF), and hybrid systems. While there is a large body of published work on coastal risk reduction via conventional infrastructure and NNBF, there is a paucity of information on Hybrid Infrastructure Systems (HIS) in the literature, especially under multi-flood hazard scenarios. This research aims to assess various HIS under multiple flood hazards for flood reduction and wildlife and habitat benefits in the coastal community of Tybee Island (Georgia, US). This community is the most densely populated barrier island in Georgia and receives over 1 million visitors each year. The Interconnected Channel and Pond Routing (ICPR) hydrodynamic model was selected to simulate hydrologic (e.g., rainfall and infiltration) and coastal (e.g., tides, storm surge, and SLR) processes, and various combinations of HIS including several conventional infrastructures (e.g., stormwater drainage system, culverts, pump systems), inland (e.g., bioswales and pocket parks) and coastal (e.g., horizontal levees and retention ponds with smart tidal gates) NNBF. Results show that NNBF can prolong the service life of conventional infrastructure in a HIS by reducing flooding stress on these structures while promoting wildlife habitats and marsh conservation by increasing the hydraulic connectivity in the tidal river system. HIS alternatives were ranked using multi-criteria decision analysis. The local government, residents, and stakeholders will select their preferred alternative for detailed design. Local studies and modeling of multi-hazard flood processes can provide insight into the performance of HIS, thus providing the opportunity to policy-makers and government agencies to improve design standards and permitting procedures for HIS at a regional scale.

At-a-station hydraulic geometry (AHG), which describes how channel width, depth, and velocity vary with discharge at a river cross section, has long been used to study fluvial processes. For example, identification of landscape and river reach drivers of hydraulic geometry can help to predict channel properties at ungaged sites and to understand channel responses to major floods. Most prior AHG studies have focused on mid-latitude, temperate regions. Tropical zones-including those affected by tropical cyclones (TCs)-have received less attention. This study analyzed spatial and temporal variability in hydraulic geometry at 24 stream gaging sites in Puerto Rico, and identified the watershed and river reach characteristics that correlate with each hydraulic geometry parameter. These characteristics were then used to build regression models of AHG parameters, with relatively high predictive power. The largest flood events from each site were found to cause systematic changes to AHG parameters; most of these floods were caused by major TCs. Upstream drainage area, average watershed elevation, watershed land cover and other characteristics were found to be significant predictors of AHG parameters. Reaches with steeper slopes were found to have limited lateral adjustability, which may reflect consolidated bank materials and valley confinement. Watersheds with high percentages of forested area showed greater changes in roughness but less vertical adjustability than more developed watersheds. These correlation results help inform whether river channel properties in Puerto Rico and similar environments are resistant to the forces of TC-induced flooding, and how these properties are affected by major floods.