Evaluating the eco-hydrologic impacts of reforestation in the Loess Plateau, China, using an eco-hydrologic model

Since the 1950s, reforestation has been widely applied in the Loess Plateau in China as a soil and water conservation measure. We examine the eco-hydrologic responses to reforestation in two neighbouring catchments in the Loess Plateau using Regional Hydro-Ecologic Simulation System. We use limited observed streamflow and other eco-hydrologic data to support and evaluate the model implementation and then apply the model to disentangle the relative roles played by inter-annual variation and longer-term trends in climate drivers and re-growth following reforestation. Our model-based analysis of trends in forest water use highlights the differences in the response of control and reforested catchments to similar declines in annual precipitation in this region over the past decades. Model estimates show that while reforestation does increase vegetation water use, the impacts on streamflow are small relative to the impact of precipitation trends on streamflow, and forest water use. Results illustrate how catchment differences in response to climate trends can confound interpretation of observed streamflow patterns in a paired catchment setting. Results also show that the greatest impact of reforestation is likely to be on groundwater recharge but also suggest that evaporation rather than transpiration is a significant contributor to hydrologic change. We also examine how declining trends in precipitation impact forest productivity. While the impact of historical precipitation declines on forest primary productivity is probably minor, model estimates suggest that forests are nearing a threshold above which further declines in precipitation will lead to more ecologically significant responses. Copyright (C) 2015 John Wiley & Sons, Ltd.