Changing Global Patterns of Urban Exposure to Flood and Drought Hazards

The studies that quantify the human and economic costs of increasing exposure of cities to various natural hazards consider climate change and increasing population and economic activity, but assume constant urban extent. Accurate estimates of the potential losses due to changing exposure of cities, however, require that we know where they will grow in the future. Here, we present the first-ever estimates of the changing exposure of urban infrastructure to floods and droughts due to urban land expansion from 2000 to 2030. Although the percent of land that is urban within the Low Elevation Coastal Zone (LECZ) increases globally only slightly to 13% by 2030, the amount of urban land is predicted to increase 230% to 234,000 km2. In 2000, about 30% of global urban land (i.e., nearly 200,000 km2) was located in the high-frequency flood zones; by 2030, this will reach 40%, (i.e., over 700,000 km2). The emerging coastal metropolitan regions in Africa and Asia will be larger than those in the developed countries and thus will have larger areas exposed to flooding. The urban extent in drylands will increase nearly 300,000 km2, reaching almost 500,000 km2. Urban land exposed to both floods and droughts is expected to increase over 250%. There are significant geographical variations in the rates and magnitudes of urban expansion exposed to floods or droughts or both. Our findings show that even without factoring in the potential impacts from climate change, the extent of urban areas exposed to flood and drought hazards will increase, respectively, 2.7 and almost 2 times by 2030. Our global view on changing geographical patterns of urban exposure to flood and drought hazards can facilitate effective mitigation and adaptation against these hazards at multiple scales.