Study On Runoff Responses To Land Use/Cover Change In Ganjiang Watershed

In this study, daily precipitation of Ganjiang watershed meteorological stations, daily runoff of Waizhou hydrological station were applied as basic data. Interannual and seasonal variation characteristics of runoff and precipitation between 1955 and 2010 were analyzed, while, this study explored the effects of precipitation on runoff in Ganjiang watershed, combined SWAT model with 1980, 1995 and 2010 years of land use / land cover data. Meantime the land use and land cover change impact on runoff in Ganjiang watershed were simulated. The following conclusions are obtained:(1) These four land use types(forest, paddy field, arid land and grassland) are primary features distributing in the Ganjiang watershed, which the area of forest is the largest with muti-year average ratio up to 60 %. Specific analyzed land use types in 1980, 1995 and 2010, the transfer between different land use types is unconspicuous from 1980 to 1995, but with complicated variation between 1995 and 2010, the area of forest, grassland decreased, inversely the paddy field, arid land, water, construction land, bare rock and unutilized land were significantly increased.(2) The muti-year average runoff of Ganjiang River Basin(Waizhou station) is 679.09 × 108 m3, which the highest runoff is 1057.51 × 108 m3 in 1973 and with the minimum runoff of 236.68 × 108 m3 in 1963. The flood season(March to July) are prone to floods and the dry season(August to February next) are vulnerable to drought, which the annual distribution of runoff indicated unbalance.(3) The muti-year average precipitation is 1573 mm in Ganjiang watershed with significantly interannual variation, which the the highest precipitation in 1975 is 2153.13 mm. Rainfall in 1963 is the lowest, only for 1066.07 mm. Characteristics of precipitation show a trend of single peak form which increase first and then decrease, the total precipitation during the first half year is higher than the last half year, the rainy season in the Ganjiang is April to June, which precipitation account for 44.1 % of total annual precipitation. Rainfall of November to January(next year) is the lowest in the watershed, accounting for only 10.6 %. Precipitation is the primary reason that causes runoff variation, and the interannual variability trend of runoff is consistent with precipitation.(4) The SWAT runoff model can be applied to the simulation of the Ganjiang watershed. Intergrating SUFI-2 algorithm in SWATCUP model with daily runoff data of Waizhou Station from 1981 to 2000, and the parameters of model were calibrated and corrected, the impact of CN2, ALPHA_BF, ESCO,GW_DELAY, GWQMN and SOL_AWC to model is high. During the rating and correction time, R2 is greater than 0.79, and E_NS is greater than 0.69, the simulation results are ideal.(5) Under the same meteorological conditions, we simulated the runoff response of the Ganjiang watershed in different land use status, by utilizing 1980, 1995 and 2010 three different land use data to alter the land use parameters, this study figured out the runoff trends kept consistent respectively in 1980, 1995 and 2010, but the runoff in 2010 is slightly higher than 1980 and 1995, which is connected with the increased of construction land, bare rock and unutilized land and decreased of forest and grassland.