Risky development: increasing exposure to natural hazards in the United States

Natural hazards damage more properties and critical infrastructure each year. Growing development in hazardous areas contributes to this trend, as disasters emerge when natural disturbances meet vulnerable assets and populations. Across the United States, ~2 million structures were built annually between 1945-2015. To evaluate how the development of hazardous areas compares with national trends, we delimited earthquake, wildfire, flood, hurricane, and tornado hazard hotspots, and overlaid them with land-use information from the novel Historical Settlement Data Compilation dataset. Our results show that 57% of structures are located in hazard hotspots, and ~1.5 million lie in hotspots for two or more hazards. Substantial levels of exposure are the legacy of decades of sustained development shaped by geographically variable socio-economic-environmental contexts. The density of structures in earthquake- or hurricane-prone areas is 3.1 and 1.7 times higher than the national average, respectively, mainly due to the densification of urban corridors in the West and Southeast. Exposure is lower for hazards that tend to affect less-developed areas, such as wildfires. However, expansion of suburban/rural development into wildlands has led to exposure growth rates up to 10 times larger than the U.S. mean. This national-scale study points to the need to better integrate exposure into risk evaluation. Moreover, high-resolution analyses of the Sacramento Valley and Houston metropolitan area highlight that differential risk assessments can be improved by considering the interaction of multiple hazards with development and mitigation efforts.