Navigating the ecosystem flood regulation service flows from subbasin to catchment in the Han River Basin

With the increasing cross-regional impact of climate change increasing in recent years, the Han River Basin, as a vital water resource supply and densely populated area in China, faces severe cross-regional flood threats and challenges. The systematic consideration of flood regulation throughout the entire upstream and downstream of the basin has become imminent. Our research aims to gain a deeper understanding of the ecosystem flood regulation service flows from upstream to downstream within subbasins and catchments scales of the Han River Basin. The results showed that the overflow path from upstream to downstream of the flood was basically consistent with the trend of the stream and the main tributaries of the Han River. It emerged that subbasins c, e, g, h and k were the key areas for the overall regulation of the upstream and downstream floods at subbasin scale. A total of 11 catchments overflow into their adjacent downstream catchments across the subbasins, a fact which is critical for catchment scale flood regulation. What’s more, there is evident interaction not only between adjacent subbasin and catchment units but also substantial exchange of service flows between non-adjacent units. Notably, catchment c’s flood regulation service flow was primarily contributed by its non-adjacent units. These findings not only contribute to filling the current knowledge gap in cross-watershed flood overflow and flood regulation service flows, but also provide support for the integrated response of upstream and downstream flood disaster risk management at the whole basin scale.