Assessment on Water Retention Function of Grassland Ecosystems in the Upper Yangtze River Basin

The upper Yangtze River basin, as an ecological protection screen for the whole Yangtze River, is a key ecological region in China. It is a substantial basis to assess the water conservation function of grassland ecosystem for sake of nature conservation, flood control and ecological regionalization. Through an integrated analysis on vegetation classification system and land-use changes, this study conducted a merger of various grasslands into eight assessment units. Interception (depth) under a single rain was formulated as the key indicator to evaluate water retention capacity of various grassland types. The results showed that the water-retention depth of grassland ecosystems within a single rainfall in the study area ranges from 17.25 mm to 40.65 mm, averaging 24.58 mm, among which the temperate-grass and forb meadow steppe had the highest capacity of water retention whereas the grass and Kobresia forb swamp meadow had the lowest capacity. A total amount of conserved water in the grassland ecosystems amounted to 45.67 × 10 $^8$ m $^3$ , pricing as $3.657×10 $^8$ . On spatial variances, the water-source area, which locates at eastern Qinghai-Tibetan Plateau, comes out to be the most important region whereas areas of Hengduan mountain region, northeastern Yunnan-Guizhou Plateau and eastern mountain ranges around Sichuan Basin co-form a generally important region.