This paper selects the typical watershed in loess plateau – Yan river watershed as the
study area .The basic database and parameter system of SWAT model are constructed to
simulate and validate the monthly runoff in the Yan river watershed. Then we studied the
runoff response to land use change in the watershed. The main conclusions of the study are
1) The basic database of SWAT model is constructed. The basic data of the Yan river
watershed are collected and processed, including DEM data, the land use data, soil data,
meteorological data and the other data SWAT model needed.
2）The SWAT model’s input parameters and its applicable value were determined.
Digital filtering method is used to calculate the base flow index, then the SWAT-CUP is
selected to calibrate and validate the input parameters, the values of 14 sensitive
parameters are determined. The five parameters which have great influence on the runoff
simulation results are: CN2 (Runoff curve number), SOL_BD (Moist bulk density),
SOL_K (Saturated hydraulic conductivity), ALPHA_BNK (Base flow alpha factor for
bank storage), GWQMN (Threshold depth of water in the shallow aquifer required for
return flow to occur).
3) To evaluate the applicability of the SWAT model in Yan river watershed. The
monthly runoff data of the Ganguyi hydrological station from 1982 to 1988 are used for
model calibration. In the calibration period, R 2 =0.74 and NS=0.69. The monthly data from
1991 to 1996 are used for model validation. In the validation period, R 2 =0.79 and NS=0.72.
The results can meet the evaluation criteria, but in the validation period simulation values
are lower than the measured values in the month with larger runoff.
4) Analysis of hydrological response to land use change show that vegetation
restoration has greate influence on stream flow, which reduces the runoff. The annual surface runoff is 30.26 mm , the annual base flow is 14.60 mm and the base flow index is
0.48 under the land use situation in 1985; The annual surface runoff is 24.03 mm , the
annual base flow is 12.87 mm and the base flow index is 0.53 under the land use situation
in 2010. The annual simulation value of stream flow is 5.21 m 3 / s at the Ganguyi
hydrological station under the land use situation in 1985. The annual simulation value of
stream flow is 4.47 m 3 / s at the Ganguyi hydrological station under the land use situation
in 2010, which decreased by 0.74 m 3 / s, the rate of change is -14.2%.
Key Words： ： Yan river watershed; Land use change; SWAT model; Runoff simulation;