Influence of urbanization on flood extent changes at the global level

Anthropogenic actions are progressively affecting most river basins worldwide, resulting in changes in hydrological processes and thus influencing water availability. Despite previous studies aimed at quantifying the relationship between urbanization and extreme flooding events at local to regional scales, it is still unclear how human presence has influenced the occurrence of seasonal surface water. As a result, global patterns remain largely unknown.

In this study, we perform a global analysis of large river basins and uncover global trends of annual maximum flood extent and impervious area, as well as their relationships with rainfall and snowmelt, over the past three decades. Hydrological and urban dynamics are computed by using multiple earth observation datasets.

We find that hydroclimatic variability alone cannot explain changes in annual maximum flood extent for 75% of the analyzed river basins worldwide. We also observe increasing trends in both annual maximum flood extent and the urbanized area within floodplains, especially in Asian and African river basins. Our findings reveal an emerging global reciprocal relationship between urbanization processes and maximum flood extent changes. Both rainfall and urbanized area can explain changes in the annual maximum flood extent in 57% of the analyzed basins.

Our findings highlight the need for a better understanding of the influence of human presence on changes in seasonal water dynamics at the global scale. In view of the worldwide rapid development of urban areas, these findings can inform the process of flood risk management and help improve targeted policy and land use interventions