Wetland mitigation functions on hydrological droughts: From drought characteristics to propagation of meteorological droughts to hydrological droughts

Wetlands have been singled out as a potential nature-based solution for improving the resilience and reducing the risks of hydrometeorological extremes. However, whether and to what extent wetlands can affect hydrological droughts is not well understood. To fill this gap, we proposed a general framework to discern the effect of wetlands on: (i) the characteristics (duration, severity, development and recovery processes) of hydrological droughts, and (ii) the propagation of meteorological droughts to hydrological droughts. First, hydrological modeling was conducted with a spatially-explicit model integrated with wetland modules. Then, the run theory and pooling method were selected to recognize hydrological drought events and identify their characteristics. Further, the Pearson correlation coefficient, temporal shift method and cross wavelet transform were used to explore the propagation processes. Finally, the characteristics and propagation processes were compared to quantify wetland mitigation services on hydrological droughts. To validate the proposed framework, two river basins from China and Canada (the Gan River Bain and the Nelson River Bain), with distinct land cover, were chosen to perform hydrological modeling and quantify wetland effects. The results indicate that wetlands mainly contribute to alleviating hydrological droughts by decelerating the development process, accelerating the recovery, shortening the duration, and reducing the severity of the hydrological drought events. However, the effects are variable as they may have weak impacts and even worsen drought conditions. Wetlands can extend drought propagation time and weaken the transition of meteorological to hydrological droughts. The likelihood of hydrological drought formation due to meteorological decreased by 19% and 18% respectively, for the Gan River Bain and Nelson River Bain, thanks to the mitigation services of wetlands. These findings highlight the drought-mitigation roles of wetlands and the proposed modelling framework has the potential to be useful in beneficial in assisting basin management on drought risks in the context of climate change mitigation.