Deciphering human influence on annual maximum flood extent at the global level

Human actions are increasingly altering most river basins worldwide, resulting in changes in hydrological processes and extreme events. Yet, global patterns of changes between seasonal surface water and urbanization remain largely unknown. Here we perform a worldwide analysis of 106 large river basins and uncover global trends of annual maximum flood extent and artificial impervious area, as proxy of urbanization, over the past three decades. We explore their relationships with hydroclimatic variability, expressed as rainfall and snowmelt, and find that hydroclimatic variability alone cannot explain changes in annual maximum flood extent in 75% of the analyzed major river basins worldwide. Considering rainfall and urban area together can explain changes in the annual maximum flood extent in 57% of the basins. Our study emphasizes the importance of understanding the global impacts of human presence on changes in seasonal water dynamics.