A new globally scalable framework applied to over 80,000 catchments shows that the conversion of rainfall into runoff is highly complex for the vast majority of the world's streams. By classifying these systems into functional types, researchers found that agricultural and urban land cover is associated with increased complexity.
The researchers applied a seasonal global framework to more than 80,000 monitored and unmonitored basins. It sorts rainfall-to-runoff response into simple, intermediate and complex types. Complexity dominated: in the dormant season, complex basins covered land amounting to 87 percent of the ungauged area assessed.[1]
The prevalence of complex catchments increases significantly during the growing season, rising by 63 per cent across the evaluated areas. Geographically, Africa and most of Asia, excluding Japan, remain predominantly complex throughout the entire year. In Europe, the proportion of complex catchments reaches 94 per cent during the growing season. Conversely, regions such as the United States' Pacific Northwest and Canada's British Columbia manage to retain simple clusters across seasons, highlighting distinct regional hydrological behaviours.[1]
A basin’s functional type can change with the season. Southeastern South America and southeastern Australia shifted from complex to intermediate. Higher shares of urban and farmed land, together with rainfall that persisted for shorter periods, were associated with greater complexity. The observational pattern identifies a relationship while leaving the direction and mechanism unresolved.[1]
