The NPP-Based Composite Indicator for Assessing the Variations of Water Provision Services at the National Scale

Water provision (WP) is an important service of the terrestrial ecosystem, which contributes to water availability for consumptive use and in situ water supply, sustains the production or flows of multiple ecosystem services (ES). Spatially explicit mapping of WP is critical for incorporating the ES concept into the decision-making processes of land-use and ecological conservation planning. Traditionally, regional complexes hydrological process models were simplified and used for mapping WP of the ecosystem at broad scales, but this approach is significantly limited by data accessibility and difficulty validating the results. To fill the gap, an NPP-based composite indicator model that simulates WP by multiplying NPP and its variations with the soil infiltration capacity factor, annual precipitation and the slope of the land surface is proposed in this paper. These parameters are chosen to map WP because they are closely related to hydrological processes. The model results were validated using observed runoff data of the eleven river basins in China. We then applied this approach to analyze the spatiotemporal changes of WP in China from 2000 to 2013. The results show that: (1) the average value of WP was lowest in the Northwest Arid Area ecoregions while the highest value of WP was in the South China ecoregion. (2) The linear trend of WP in the Loess Plateau and Hengduan Mountains ecoregions were increased while decreased in the other nine ecoregions. (3) The WP in the north of the Qinghai-Tibet Plateau presented a significant decrease trend mostly because the land cover change (e.g., grassland convert into dessert) and decreasing precipitation; the decreasing of the WP in Yunan-Guizhou Plateau are because the farmland convert into settlement land and the significant decrease of precipitation and significantly increase of temperature; the significant increase of the WP in Northeast China are because the increasing of forest and farmland, the grassland and wetland convert into farmland and forest, and the significant decrease of temperature and increase of precipitation; Although the increase of precipitation has played an important role in promoting WP, the significant increase of WP in the Loess Plateau was mainly due to the farmland convert into forest and grassland ecosystem types. The indicator explored by this research is benefiting for revealing the variations of WP under different land-use change and climate change, and informed the decision-making process of land-use policy or conservation planning at data-scarce regions or broaden spatial scales.