Flood protection ecosystem services in the coast of Puerto Rico: Associations between extreme weather, flood hazard mitigation and gastrointestinal illness.

Floods are becoming increasingly influential in coastal cities due to the intensification of extreme weather events. The impacts of flooding go beyond damages to infrastructure, it also affects human health. During floods, discharge of sewage into streets increases exposure to pathogens causing gastrointestinal (GI) illnesses. A potential strategy for coastal protection during weather hazards is the use of flood protection ecosystem services, but their effectiveness at ameliorating the impact of floods on GI illnesses remain understudied. Here we explore the relationship between extreme rainfall, flood protection ecosystem services, and the occurrence of Medicare claims for gastrointestinal (GI) illnesses in Puerto Rico. We first conducted model averaging to detect variables explaining flood impact for the years (1999-2014), and then used these variables as predictors in a spatio-temporal analysis of GI illness in the same period (1999-2013). Our results show that flood impact varies proportionally with extreme rainfall, and inversely with flood protection ecosystem services, particularly due to the presence of karst soils. The protective effect of karst soils is lost when there is a high percentage of people living in flood prone areas, as suggested by a significant interaction effect between these two variables. In support of our hypotheses, cases of GI illness also spike after extreme rainfall events and are affected by the interaction effect of karst soils and people living in flood prone areas. Our results support the linkage between extreme weather events, flood damages and GI illnesses, and suggests a buffering role of ecosystem services that promote rainfall infiltration. The relevance of these ecosystem services, however, is affected by planning decisions such as residential development in flood prone areas. Our results help inform planning strategies for future weather hazards, accounting for the role of natural and built infrastructure on minimizing flood impacts and human health effects.