Research On Hydrological Responses To LUCC Based On SWAT In Yongjiang Basin

The simulation study of LUCC (Land use and Land cover Change) environmentaleffects is a hot issue in current LUCC research. Meanwhile, hydrological effect ofLUCC is one of the important environmental effects. Thence, in-depth analyses theLUCC driving mechanism to establish the connection between LUCC andhydrological change is an effective means to resolve regional ecology, resource andenvironmental issues.In this study, taking Yongjiang basin as the study area, future LUCCs from theyear of2000to2020were predicted and analyzed by CA_Markov model. Throughsimulating surface runoff of different LUCC scenarios, we analyzed the impact ofdifferent land use scenarios on runoff. Besides, suitable land management measuresfor the watershed were proposed, which is aimed at providing a scientific basis foroptimizing management of land and water resources.The main research conclusions are as follows:(1) Elevation, slope and aspect affected spatial distribution of different land usetypes, the arable land mostly concentrated in the flat or gentle slope area within200m,and it showed an increasing trend with the elevation from2000to2010. Moreover,the woodland dominated in the area above200m, in which it reduced from2000to2010yet. In addition, the residential and construction land showed significantincreases year by year, and increasingly gathered to area of smaller slope and within100-200m. Besides, the proportions of wetlands and unused land were small, and theinterannual variability and elevation changes were not so obvious.(2)Analyzed the Spatial-Temporal variations of NDVI data,The results showedthat: The average values of NDVI in Yongjiang basin were high in the ambient, butwere low in the middle. The values of NDVI in vegetation coverage area in Yongjiangbasin fluctuated in the range of0.42-0.54, NDVI showed high fluctuations from2000to2004, but slow growth trend since2004NDVI in the Yongjiang basin wererelatively stable,92.87%of vegetation covered area presented a medium-lowvariability, only7.13%area showed high fluctuations; During the period of2000-2010,the area where the value of NDVI increased was much larger than the areawhere the value of NDVI reduced, the improved area occupied56.02%of vegetationcovered area, and the depraved area was account for13.36%and30.62%arearemained unchanged. (3) The LUCC in the year of2010was simulated by CA-Markov model, and itwas compared with the actual LUCC that year. It was found that CA-Markov modelcould simulate the change trend with the number accuracy generally greater than85%and spatial accuracy greater than80%. LUCC simulation result in2020showed thewatershed land use area in descending order is: arable land> woodland> grassland>construction Land> wetlands> other sites. The arable land and woodland dominated inall land use types, and both areas accounted for77.11%of the total area. However,construction land accounting for only7.42%, but the impact of its changes in thespatial distribution and quality on the ecological environment could not be ignored.During2010and2020, the main conversions of land use types were that within inwoodland and arable land, woodland and grassland, the construction land and arableland as well as woodland.（4）Firstly, the study built the database for SWAT model by using ArcGIS,divided Yongjiang basin into144sub_basins and1848HRUs. And then,analyzed theparameter’s sensitivity of the SWAT model, And studied changes of climate andrunoff using Mann-Kendall trend analysis since1981. At last, datas from1981to1995were chosen to calibrate the model and datas were chosen as the verificationdates since1996, achieved better simulate effects by adjusting the model parametersfinally.(NS=0.522; R2=0.59)（5）Analysis changes of precipitation and runoff, the result showed that therunoff changes mainly affected by rainfall and other climatic conditions, the averagemonthly runoff and rainfall showed a strong positive correlation and runoff responsesto rainfall have a certain lag; Similarly, the significant and positive correlation wasemerged between the annual precipitation and annual runoff, Interannual variability ofannual runoff was larger and the overall downward trend in volatility;With the NDVIincreased year by year, the average annual flow was reduced accordingly.（6）Simulated characteristics of runoff under different LUCC, the results showthat the runoff decreased gradually since2000and coincided with the measured data;To quantify runoff responses for different land use/cover scenarios, the researchinvestigated responses for the runoff from F1to F4by established different land use/cover scenarios in the future, concluded that, compared with the existing situation,，the runoff would increase in varying degrees in Yongjiang basin.