Large-scale comparison of flow-variability dampening by lakes and wetlands in the landscape

Considering the potential of wetlands to dampen temporal variability of water flow through the landscape, they are increasingly considered as possible nature-based solutions to mitigate risks of flooding and drought. In this study, we investigate flow variability by means of a flow dampening factor and use observation data from 1984 to 2013 for 82 Swedish catchments to statistically and comparatively analyze the large-scale effects on this factor of multiple wetlands and lakes in the landscape. The results show good correlation between large-scale flow dampening and relative area of lakes and floodplain wetlands within a catchment. An increase in relative area up to around 15% for lakes and 0.5% for floodplain wetlands lowers the temporal standard deviation of runoff (R) to around 10%-15% of that for precipitation (P), compared with a common flow-variability dampening of around 35% for catchments with lake-wetland area close to zero. Further increase in these relative areas, or in those of wetland types other than floodplain wetlands, has little or no flow dampening effect. The results indicate that the large-scale flow dampening effect of lakes and floodplain wetlands is mainly due to their water-storage capacity and less due to their possible effects on the partitioning of P between R and evapotranspiration. Overall, the results emphasize the importance of accounting for the problem scale and relative water-storage capacity of wetlands when considering their large-scale efficiency as possible nature-based solutions for large-scale flow-variability regulation in whole catchments.