Global Estimation of River Bankfull Discharge Reveals Distinct Flood Recurrences Across Different Climate Zones

The maximum amount of water rivers can transport before flooding is known as the bankfull discharge, an essential threshold for flood risk and biogeochemical cycles. Current Global Flood Models rely on an untested assumption of a spatially-invariant, 2-year bankfull recurrence. Here, based on observations and machine learning, we deliver the first global estimation of bankfull discharge in different climates along a new bifurcating river network at ~ 1 km spatial resolution. In contrast to the 2-year assumption, we find rivers flood more frequently in tropical and temperate regions (median return periods of 1.5 and 1.8 years; IQR 2.5 and 3.2y, respectively), and less frequently in cold and arid regions (2.8/4.3 years; IQR 4.8/6.0y). Relative to observations, the 2-year assumption overestimates bankfull discharge in the tropics (54%±78%, mean ± std) and underestimates it in arid regions (10%±51%). This new understanding will transform our ability to make accurate global flood predictions.