Projection of future hydrometeorological extremes and wetland flood mitigation services with different global warming levels: A case study in the Nenjiang river basin

It is common to conceptualize wetlands as a nature-based flood defense for improving basin resilience to climate change. Yet, such a solution is often ignored when projecting or assessing river flood risk under future climate change. To fill this gap, we apply a hydrological modeling platform integrating wetland modules to a 297,000-km2 large river basin in Northeast China under different climate change scenarios. The overarching goal of this study is to predict future precipitation extremes and flood events, and to explore whether and to what extent wetlands can effectively mitigate the risk of future flood at the basin scale. We first assessed the trend in future precipitation extremes extracted from multi-global climate models (GCMs) and found that the future precipitation extremes will increase both under RCP4.5 and RCP 8.5 scenarios. The increasing precipitation extremes, therefore, are projected to bring about higher flood risks with the increase in warming levels. Wetlands can suppress flood duration, mean flow, volume, and peak by 1.9–10.2%, 4.6–7.1%, 8.7–15.7% and 12.5–14.1% under future climate change in this large river basin, respectively. Our study found that wetlands can attenuate the risk of floods with a 2- and 5-year return period to a great extent. However, the wetland mitigation function is limited to floods with a 10-, 20-, and 50- return, and even failed to extreme floods with a 100- and 200-year return. These findings imply that future precipitation extremes will cause flood risks in this large river basin that cannot be mitigated by its wetlands, and substantial wetland restoration is needed to enhance the capacity of their service in order to improve the basin’s resilience to future flood risks.