Abstract
Large–scale ecological restoration programs are considered as one of the key strategies to enhance ecosystem services. The Headstream region of Yangtze River (HYZR), which is claimed to be China’s Water Tower but witnessed the rapid grassland deterioration during 1970s–2000, has seen a series of grassland restoration programs since 2000. But few studies have thoroughly estimated the hydrological effect of this recent grassland restoration. Here we show that restoration significantly reduces growing-season water yield coefficient (WYC) from 0.37 ± 0.07 during 1982–1999 to 0.24 ± 0.07 during 2000–2012. Increased evapotranspiration (ET) is identified as the main driver for the observed decline in WYC. After factoring out climate change effects, vegetation restoration reduces streamflow by 9.75 ± 0.48 mm from the period 1982–1999 to the period 2000–2012, amounting to 16.4 ± 0. 80% of climatological growing-season streamflow. In contrary to water yield, restoration is conducive to soil water retention – an argument that is supported by long-term in-situ grazing exclusion experiment. Grassland restoration therefore improves local soil water conditions but undercuts gain in downstream water resources associated with precipitation increases.
Highlights
The headstream region of Yangtze River on the Tibetan Plateau covers ~17% of the whole Yangtze River basin and provides nearly 20% of the water volume of the Yangtze River[1]
Have similar negative impacts on water resources occurred after grassland restoration over the Headstream Region of Yangtze River (HYZR)? Answering this question could provide guidance for developing policies associated with ecosystem restoration over degraded semi-arid and/or arid regions
We evaluate the impact of recent grassland restoration on water resources in the headstream of Yangtze River based on the Budyko framework and an offline atmospheric moisture tracking model, with the simultaneous use of streamflow observations, a model-data fusion product blending process-based understanding with multi-satellite observations of climatic and environmental variables[17], and in-situ long-term grazing exclusion experiments
Summary
Observed decline of water yield coefficient at the catchment scale. To test if the decline of WYC could depend on the choice of a climate forcing dataset, we used different precipitation products (Fig. 2B). We show that the WYC declines during the post-restoration period, but the streamflow at the outlet of HYZR do exhibit an increase of 14.6 mm during the post-restoration period relative to the pre-restoration period This seemingly paradox arises from a corresponding increase of catchment-scale precipitation (73.5 mm) based on MSWEP during the latter period. The quantification of grassland regeneration on water yield change is complicated by accompanied climate change. This decline is, over-compensated by an increase of 24.4 mm due to climate change resulting in an observed increase of 14.6 mm in streamflow (Fig. 3C). Variables Soil water content (mm) Bulk density (g cm−3) MSWHC (mm) Aboveground biomass (g m−2)
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