Developing a decision support tool for China's re-vegetation program: Simulating regional impacts of afforestation on average annual streamflow in the Loess Plateau

China is facing increased environmental pressures as its economy rapidly develops, with shortages of water potentially limiting development—especially in its dryer north and west. The highly erodible Loess Plateau in the Yellow River Basin is the main source of high sediment loads resulting in poor water quality. Engineering and re-vegetation measures have been (and are being) widely implemented to reduce these environmental problems, but it has since been found that re-vegetation activities result in a decrease of streamflow. Given that water resources are currently over allocated in the Yellow River Basin (as seen by the river increasingly not reaching the sea), the external hydrological impacts from current and planned re-vegetation activities need to be taken into account by a wide range of natural resources managers and policy makers. To increase the awareness of the hydrology-landuse change implications in the region, a decision support tool called Re-Vegetation Impacts on Hydrology (ReVegIH) has been developed. To maximize use of the tool, the design of ReVegIH has been participatory with the final design of the functionality actively taking account of user requirements and needs. ReVegIH provides a means for users to: (1) determine where priority (and target) re-vegetation activities should be undertaken; (2) ascertain what species are suitable for a specific location; (3) simulate the related hydrological impact on an average annual basis. The spatial resolution of the first two functions is provided at 100 m, while the third is at the catchment (or county) level for the 113,000 km2 study site, called the Coarse Sandy Hilly Catchment, which drains the main south flowing branch of the Yellow River. ReVegIH assesses afforestation impacts on average annual streamflow via application of an aerial-weighted evapotranspiration model operating at steady-state forced by long-term (21-year) annual average meteorological data and landuse scenarios. ReVegIH does not consider the changes in annual streamflow following observed 21-year trends of annual precipitation and pan evaporation data, nor as a function of time since afforestation, and the ability to simulate the hydrological impact due to establishing plantations in different areas in the landscape through time is not included.