Global Changes in 20?Year, 50?Year, and 100?Year River Floods

Abstract Concepts like the 100-year flood event can be misleading if they are not updated to reflect significant changes over time. Here, we model observed annual maximum daily streamflow using a nonstationary approach provide first global picture of in: (a) magnitudes 20-, 50-, and floods (i.e., flows given exceedance probability in each year); (b) return periods floods, as assessed 1970 fixed magnitude); (c) corresponding probabilities. Empirically, find 20-/50-year have mostly increased temperate climate zones, but decreased arid, tropical, polar, cold zones. In contrast, arid/temperate zones exhibit mixed trends results influenced by small number stations with long records, highlight need for continued updating hazard assessments.