Abstract: The Pi River, the largest tributary of the Huai River on its southern bank, was selected as subject for study to quantitatively evaluate effects of changes in land use on relationship between rainfall and surface runoff, using the SWAT (soil and water assessment tool) distributed mechanism hydrological model. The change in land use during the years of 1996-2010 was mainly reflected in conversion of upland fields and paddy fields into construction land, and of forestland into gardens. Comparison of 2010 with 1996 shows that the former was 5.87% higher than the latter in annual runoff, and the increase was mainly observed in runoff only during the flooding season, while during the non-flooding season, a declining trend was observed, thus expanding amplitude of the fluctuation of runoff within a year. Annual runoff differed from year to year. In normal hydrological years, the response to changes in land use was the most significant and the greatest in amplitude. The response was greater in dry years than in flooding years. The results show that the water conservation capacity of the Pi River Valley is obviously on the decline.

Key words: land use changes, hydrological response, SWAT model, Pi River Valley