Increased urban exposure to flooding from 1985 to 2015

Abstract:

Large river floods plague many urban areas worldwide, resulting in the loss of lives and consequential long-lasting economic burden. The historical increased river flood risk is mainly associated with the socioeconomic development and urbanization in the flood-risk zones. Impacts of urbanization patterns on flood risk in the past is essential information for wiser urban planning and risk mitigation in the future. To provide a historical perspective of urbanization impacts on flood risk, we assess the global urban exposure dynamic (1985-2015) to big river flood based on a novel high spatiotemporal resolution urban change dataset (30m) and several state-of-art flood hazard maps. According to our analyses, the rapid urbanization in the last three decades has significantly increased urban exposure to high-end flood events. The growth rate of urban exposure in many countries even exceeds the urbanization rate. In developing countries, especially in China, rapidly expanding mega-cities in the floodplain with less risk-free land contributed the major urban exposures increase. These results reveal a considerable flood risk due to increasing unplanned or planned urbanization in the flood-risk zones, suggesting the urgency of risk management by sustainable urban development in the flood hazard area.