Hydrological Response To Land Use Change In Wangkuai Reservoir Basin

Wangkuai reservoir is one of the important water supply sources of Baiyangdian Lake.In recent decades,the inflow flow of Wangkuai reservoir has gradually decreased.In addition to climate change factors such as rainfall and temperature,land use change caused by human activities is also an important factor affecting water resources in the region.The analysis of the response mechanism of hydrological process of Wangkuai reservoir basin to the change of land use pattern can provide an important scientific basis for the rational construction of land use pattern and the sustainable utilization of water resources in Wangkuai reservoir basin.Based on the data of land use in 1980,2005 and 2010,this paper uses arcgis 10.3 and frgstats 4.2 software to calculate the land use transfer matrix and landscape pattern index,and analyzes the spatial-temporal change characteristics of land use area and pattern in Wangkuai reservoir basin.SWAT model is applied to construct the distributed hydrological model for Wangkuai Reservoir basin Type B:simulate and analyze the impact of land use and landscape pattern change on runoff spatial-temporal distribution,runoff coefficient,annual runoff variation coefficient and annual conservation index of Wangkuai Reservoir Basin;use correlation analysis and redundancy analysis(RDA)to quantitatively analyze the relationship between land use pattern and runoff.The main contents and results of this paper are as follows:(1)Based on the land use data of Wangkuai Reservoir Basin in 1980,2005 and 2010,woodland and grassland are the main land use types of Wangkuai Reservoir Basin,and the sum of them accounts for more than 90%of the total area of the basin.The comprehensive land use dynamic degree(LC)of Wangkuai Reservoir Basin was 0.01%in 1980-2005,and 6.29%in 2005-2010.Based on the land use transfer matrix,from 2005 to 2010,the area of forest land increased by 2029.24 km2,mainly from the transfer of grassland(1889.99 km2)and cultivated land(114.17 km2).(2)The landscape pattern indexes of 1980,2005 and 2010 were calculated by frgstats 4.2.On the landscape level,the increase of NP,PD,LSI and contract in Wangkuai reservoir basin indicates that the fragmentation degree of the basin is deepening,and the overall shape of the landscape tends to be complex;the gradual decrease of SHDI and Shei indicates that the land use type is gradually single,and the landscape heterogeneity is low.At the level of patch type,after 2005,the fragmentation degree of grassland deepened,the complexity of patch shape increased;the fragmentation degree of forest land weakened,the dominance increased significantly,and the patch shape tended to simplify.(3)According to the analysis of the measured runoff data of Wangkuai reservoir from 1986 to 2018,the annual runoff fluctuates with time,and the monthly runoff distribution of Wangkuai reservoir is unbalanced within the year,mainly focusing on the m-k mutation test and periodic analysis in July to September.The mutation point of annual runoff of Wangkuai reservoir are 1997 and 1994.There is the kind of periodicity of roots in 2-11 years,and the periodicity of 7 years is the strongest.According to DEM,land use data,soil type data,rainfall temperature and other meteorological data of Wangkuai Reservoir Basin,spatial database and attribute database are established,23 sub basins and 81 hydrological response units are divided,and SWAT model is preliminarily established.Using swat-cup software to calibrate the parameters,12 sensitive parameters were identified.The values of R2 and ENS are 0.79 and 0.78 in the validation period of the model,which shows that the simulation results of SWAT model are basically consistent with the measured values,and it has good applicability in Wangkuai reservoir basin.(4)According to the scenario simulation method,three land use scenarios are set up:historical land use scenario,natural development land use scenario and extreme land use scenario.Historical land use scenarios(1980,2005,2010),and runoff decreases with time.In 1980 and 2005,the annual average runoff decreased by 02.9 million m3;in 2010,compared with 2005,the annual average runoff decreased by 51 million m3.Spatially,except for the increase of sub basin 2,the annual average runoff of other sub basins decreased.The CA Markov model is applied to predict the land use scenario in 2025 as a natural development land use scenario.SWAT model is applied to simulate the response of annual runoff,runoff coefficient,annual runoff coefficient and annual conservation index in 2025 and extreme land use scenarios(scenario 1:agricultural land,scenario 2:forest land,scenario 3:grassland).The results show that:compared with the 2010 land use scenario,under the natural development scenario and the extreme land use scenario,the annual average annual,monthly runoff,runoff coefficient and annual runoff variation coefficient change rule are the same,which are S1 scenario>S3 scenario>2010 scenario>2025 scenario>S2 scenario;the inclusion index is S2 scenario>2025 scenario>2010 scenario>S3 scenario>S1 scenario.(5)Based on correlation analysis and redundancy analysis(RDA),the relationship between land use pattern change and runoff was identified.The results showed that forest land and grassland were negatively correlated with runoff,while agricultural land and artificial surface were positively correlated with runoff.At landscape level,patch density(PD)and patch number(NP)were negatively correlated with runoff and runoff coefficient,while Contag was positively correlated with runoff and runoff coefficient.At the patch type level,the maximum patch index(LPI)of agricultural land was positively correlated with runoff,while the patch number(NP),boundary density(ED),dispersion and juxtaposition index(Iji),shape index(LSI)were negatively correlated with runoff and runoff coefficient,but the correlation was not significant.For woodland and grassland,the number of patches(NP),maximum patch index(LPI),shape index(LSI),boundary density(ED),dispersion and juxtaposition index(Iji)were negatively correlated with runoff and runoff coefficient.Due to the small proportion of agricultural land and artificial surface,the main reason for the decrease of runoff in Wangkuai reservoir basin is the increase of forest land,the increase of landscape area and the simplification of landscape shape.