Wetland-based solutions against extreme flood and severe drought: Efficiency evaluation of risk mitigation

The hydrological regulation services provided by wetlands have great potential to be used as a nature-based solution for improving basin resilience to hydrological extremes. However, the efficiency of wetlands in attenuating hydrological extremes and how this attenuation efficiency varies with the location and type of wetland are not well understood. Here, we used a distributed hydrological modeling platform coupled with isolated and riparian wetland modules (IWs and RWs) to (i) quantify the impacts of wetlands on extreme flood and severe drought and (2) investigate the influences of geographical location and types of wetlands on their regulation efficiency. The hydrological modeling was conducted with various wetland loss scenarios on the Nenjiang River Basin (NRB)- a large river basin where wetlands are abundant and play an important hydrological regulation function. Modeling results showed that RWs mainly decreased peak flow and reduced downstream flood volume. However, IWs predominantly decreased flood volume and slightly mitigated peak flow in the entire NRB. For severe drought, RWs overall alleviated drought while IWs could intensify drought deficit to some extent. In terms of geographical location, upstream wetland obviously amplified downstream flood risks whereas alleviated drought intensity by providing source water for downstream during drought period. Downstream wetland exerted strong hydrological influence on extreme floods and severe droughts and should be restored and conserved preferentially to promote basin hydrologic resilience in the NRB. The methodology in this study can also be applied to other study areas for decision and management when considering spatial distribution and types of wetland restoration for promoting basin hydrologic resilience.