| Revealing the effects of climate variability and land use change on soil erosion were of great significance to the development of regional ecological restoration and water and soil ecological control.Therefore,the Wohushan Basin of Ji'nan was selected as the research object in this study.The methods including Mann-Kendall test,moving t-test,wavelet periodic analysis,thiessen polygon method and spatial interpolation were selected to analyze the temporal and spatial variation characteristics of hydrometeorological elements.Based on the experimental results of artificial rainfall simulation,the effects of climate variability and land use change on soil erosion were discussed by using SWAT model,RUSLE model of soil erosion and scenarios setting.The main achievements of this study were as following:(1)The annual rainfall,temperature and runoff in study area showed no significant increasing trend,while the evaporation showed a significant decreasing trend during 1980-2016.The average annual rainfall was 731.34 mm,and there were three kinds of periodic variation rules of 4-10,12-22 and 23-32 years.The spatial distribution of the average annual rainfall in the study area was uneven,decreasing gradually from east to west.The average annual temperature was 14.7?,and periodical variation was 25-30 years.The average annual evaporation was 2010.05 mm,and the periodical changes were 5-12 years and 25-30 years.The average annual runoff was 5951.79×104 m3,with two kind of periodical variations of 5-10 and 12-20 scales.(2)Runoff and sediment yields on slopes were studied by setting up four slope types of 10,15,20 and 25°,five rainfall intensities of 30,40,60,80 and 100 mm/h,six planting patterns of random planting,block planting,strip planting,slope bottom planting,slope middle planting,slope top planting,three vegetation allocation of pure grass allocation,pure shrub allocation and grass-shrub allocation,and three vegetation coverage of 25%,50%and 75%.With the increase of slope,the runoff and sediment yield increased first and then decreased.When the rainfall intensity was 30 and 100 mm/h,the runoff yield of four slope types was respectively 66.12 L,86.89 L,102.36 L,94.51 L and 155.00 L,173.00 L,210.15 L,179.00 L.And the sediment yield was respectively 92.66 g?120.89 g?135.68 g?129.77 g and 172.59 g?214.65 g?264.32 g?245.24 g.The runoff and sediment yield on the slope increased with the increase of rainfall intensity.When the slope was 20°,the runoff and sediment yield under the rainfall intensity of 30-100 mm/h were respectively 102.36 L,124.56 L,155.54 L,172.58 L,210.15 L and 135.68 g,156.58 g,78.21 g,221.58 g,264.32 g.The runoff rate increased first and then stabilized with time,while the sediment concentration increased first,then decreased to stable value.When the slope was 20°and the rainfall intensity was 30 mm/h,the order of runoff yield of different planting patterns from small to large was random planting(57.23 L)<block planting(69.43 L)<strip planting(71.21 L)<slope middle planting(80.07 L)<slope bottom planting(85.06 L)<slope top planting(94.43 L),while the order of sediment yield from small to large was slope bottom planting(68.24 g)<random planting(83.54 g)<block planting(92.45 g)<slope top planting(105.64 g)<slope middle planting(116.25 g)<strip planting 125.32 g).When the slope,the rainfall intensity and the vegetation coverage were respectively 20°,30 mm/h and 50%,the runoff and sediment yields of different vegetation allocation from small to large were grass-shrub allocation(72.24 L,81.32 g)<pure grass allocation(76.07 L,86.24 g)<pure irrigation allocation(81.34 L,96.54 g).And,with the increase of vegetation coverage,the runoff and sediment yield were reduced significantly.(3)Applicability of runoff simulation in the Wohushan Basin based on SWAT model was good.The results showed that the correlation coefficient R2 and Nash efficiency coefficient NSE were 0.85 and 0.82 in the calibration period,and the R2 and NSE were 0.89 and 0.88 in the validation period.(4)The intensity of soil erosion in 1988,2002,2009 and 2014 was slightly erosion,and the moderate erosion occurred in 1996.With the elevation increases,the erosion modulus and amount increase first and then decrease,and reached the largest in the range of 300-500 m.With the increase of slope gradient,the soil erosion modulus and amount increased first and then decreased.The largest modulus of soil erosion was in the range of 15-20°,while the largest amount of soil erosion was in the range of 25-35°.The order of average erosion modulus of different slope directions from large to small was sunny slope>semi-sunny slope>semi-shady slope>shady slope,and the order of soil erosion amount from large to small was semi-sunny slope>sunny slope>shady slope>semi-shady slope.(5)By simulating the hydrological response under extreme land use scenarios and combining the land use and topographic characteristics of the basin,the land use types of the basin were optimized to simulate the runoff and soil erosion processes.Compared with the simulated runoff in 2014,the average annual runoff decreased by 483x 104 m3 and the reduction ratio was 8.71%.The modulus of soil erosion decreased from 942.23 t·km-2·a-1 to 804.81 t·km-2·a-1,and the amount of soil erosion decreased from 50.79×104t to 43.38×104t,which decreased 14.59%.(6)The simulation results of runoff under different climate variability scenarios showed that runoff was more sensitive to rainfall than to temperature.When the rainfall increased 10%,the runoff increased 17.42%,and when rainfall decreased 10%,the runoff decreased 13.37%.The average annual runoff showed a decreasing trend with the increase or decrease of temperature.When the temperature increased or decreased 1?,the average annual runoff decreased by 1.67%and 3.39%. |
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