RESEARCH OF HYDROLOGICAL RESPONSES TO LAND-USE VARIABILITY IN A SEMIARID WATERSHED BASED ON SWAT MODEL

The Soil and Water Assessment Tool (SWAT, 2009) model was used to simulate hydrological response affected by land-use changes for long periods in the main stream of Zhuozhang River. The calibration (R-2 = 0.84, Ens = 0.80) and validation (R-2 = 0.72, Ens = 0.69) results were satisfactory for the outlet of the watershed. Four scenarios were set up and put into calibrated SWAT. Land-use changes had no significant effects on annual runoff during the months with limited precipitation and runoff. During the flood season, scenarios of "Return the grain plots to forestry" and "grassland" contributed to the increase of runoff while "Increase cultivated land area appropriately" and "Exploit reserved resources" would decrease runoff. Runoff in scenario b "Return the grain plots to grassland" was smaller than that in scenario a "Return the grain plots to forestry", but still had the positive effect on runoff. Runoff contribution coefficients (RCCs) by unit areas of FRSD, FRS2, RNG2, AGRR and URML were -1.98 m(3)ha(-1), 8.89 m(3)ha(-1), 6.51 m(3)ha(-1), -3.36 m(3)ha(-1), and 6.39 m(3)ha(-1), respectively. For unit areas, the order of runoff contribution capability of each land-use was FRS2>RNG2>URHD>AGRR>FRSD. RCCs of FRS2, RNG2 and URHD were positive, and represented the area of three types of land-use being consistent with runoff while RCCs of FRSD and AGRR were negative which meant runoff would decrease with the increase of these two types of land-use.