Insights on expected streamflow response to land-cover restoration

Abstract

Ecosystem service approaches to watershed management have grown quickly, increasing the importance of understanding the streamflow response to realistic land-cover change. Previous work has investigated the relationship between watershed characteristics and streamflow in catchments around the world, but little has focused on systematic relationships between watershed characteristics and streamflow change after land-cover restoration. To address this gap, we simulate streamflow responses to restoring 10% of watershed area from agricultural land to forest and natural pasture in 29 watersheds around the world. This change is consistent with that performed in watershed-service programs. We calculate the change in a broad array of streamflow indices for each site and use a graph-connectedness approach to cluster the sites based on the sign of the index value changes. We find three primary clusters with distinct responses to restoration. Permutation tests and effect sizes demonstrate the difference in watershed characteristics and streamflow indices across clusters. The low-flow intensifying sites have shallower soils and smaller saturated soil volumes. After restoration, simulated streamflow in these sites increases during relatively dry periods and declines during high-flow periods. The high-flow intensifying sites have larger saturated soil volumes. After restoration, simulated dry-season flow in these sites decreases. The high-flow enhancing sites have larger soil hydraulic conductivities than the high-flow intensifying sites. After restoration, simulated dry-season flow in these sites decreases less than in high-flow intensifying sites. The soil depth and hydraulic conductivity appear to be the characteristics that determine clusters, as clusters are not statistically related to climate, watershed location, proximity, size and shape, elevation, or pre-existing land cover. This study provides valuable understanding of land-cover restoration and the watershed characteristics that most impact streamflow change.