Global evidence of rapid urban growth in flood zones since 1985

Abstract

As countries urbanize, human settlements are rapidly expanding into hazardous ood zones. This study provides a global analysis of spatial urbanization patterns and the evolution of ood exposure between 1985 and 2015. Using high-resolution annual data, it shows that settlements across the world grew by 85 percent to over 1.28 million square kilometers. In the same period, settlements exposed to the highest ood hazard level increased by 122 percent. In many regions, risky growth is outpacing safe growth, particularly in East Asia, where high risk settlements have expanded 60 percent faster than safe ones. Developing countries are driving the recent growth of ood exposure: 82 percent of the 36,500 square kilometers of settlements built in the world's highest-risk zones since 1985 are in low-and middle-income countries. In comparison, recent growth in high-income countries has been relatively slow and safe. These results document a divergence in countries' exposure to ood hazards. Rather than adapting their exposure to climatic hazards, many countries are actively increasing their exposure. introduction Disaster losses are rising, and evidence is mounting that climate change is driving up the probability of extreme natural shocks 1,2,3,4 . Yet, it has also proven politically expedient to invoke climate change as an exogenous force that supposedly places disasters beyond the in uence of local planners and authorities 5,6 . However, locally determined patterns of urbanization and spatial development are key factors to people's exposure and vulnerability to climatic shocks 7 . In this study we show that since 1985 human settlements around the world -from rural villages to large cities -have expanded continuously and rapidly into present ood zones. Globally, settlement growth in high-risk zones is outpacing growth in safe zones by a large margin. This provides systematic evidence that rather than adapting to increasingly frequent climatic shocks, countries around the world are actively increasing their exposure to ood hazards.

Changes in Population Exposure to Rainstorm Waterlogging for Different Return Periods in the Xiong’an New Area, China

“…Urbanization also leads to the rapid expansion of residential areas, industrial parks, and other infrastructure. Studies have shown that regions experiencing rapid urbanization are often prone to flooding [65]. Future urban waterlogging simulations should pay more attention to the impacts of urbanization.…”

Extracting Spatiotemporal Flood Information from News Texts Using Machine Learning for a National Dataset in China

“…Urbanization leads to changes from natural surfaces such as soil and vegetation to impervious materials like asphalt, which prevents rainfall from effectively seeping into the ground, accelerating the speed of runoff and thus increasing flood risk (Huong and Pathirana, 2013;Luo and Zhang, 2022). Notably, China has been the largest contributor to the global expansion in high-hazard settlements in flood zones, reflecting the impact of its rapid urban growth (Rentschler et al, 2023).…”

Influence of building collapse on pluvial and fluvial flood inundation of metro stations in central Shanghai

“…Climate change and urbanization have increased human exposure to urban flood hazards, particularly in the East Asia (Cao et al, 2022;Rentschler et al, 2023). To enhance urban resilience to flood hazards, there is an urgent need to understand the physical processes of flood propagation under various current and future scenarios.…”