Study On Landscape Pattern Evolution And Evapotranspiration In The Upper Reaches Of Xilin River Basin

Located in the middle of Inner Mongolia autonomous region,Xilingol grassland is an important ecological barrier in north China.Over the past 30 years,with the frequent occurrence of extreme weather and the impact of overgrazing,the ecological environment in this area has been seriously deteriorated.In the inland river basins of arid and semi-arid grasslands where water resources are in short supply and the ecological environment is extremely fragile,it is urgent to carry out basic research on eco-hydrology and clarify the rules of regional landscape pattern succession and evapotranspiration,so as to support the protection and restoration of grassland ecological environment.This paper takes the upper reaches of Xilin River Basin as a typical research area,uses the Landsat 8 data from 1989 to 2015,and the relevant theories and methods of landscape ecology to quantitatively analyze the dynamic change characteristics of landscape pattern in the research area in the past 30 years,and discusses its driving mechanism.On this basis,the SEBAL model was used to estimate the evapotranspiration in the growing season of the upper reaches of the river basin from 2015 to 2017,and the applicability of the model was evaluated to further explore the spatial and temporal distribution of evapotranspiration in the upper reaches of the river basin and its variation law on the landscape scale.The main research results obtained in this paper are as follows:(1)Grassland is the main landscape in the upper reaches of the river basin,followed by marshland,farmland and water.In the past 30 years,the marshland showed a decreasing trend,and the change rate was-1.21km2·a-1,while the grassland,farmland and water showed an increasing trend,with the growth rates of 0.72km2·a-1,0.42km2·a-1 and 0.02km2·a-1.The spatial and temporal pattern of the grassland landscape in the nearly 30a watershed basically remains unchanged,the cultivated land shows a change of expansion from east to west,the mass center of the swamp moves to the northwest as a whole,the patch area shrinks in the south-north direction,but extends in the east-west direction,and the water body changes in a discrete trend.According to the analysis of landscape index,the connectivity of grassland,water body and cultivated land is good,while that of marsh is poor from 1989 to 2015.The patches of grassland,farmland,marsh and water landscape are concentrated.The integrity of grassland,water and cultivated land is better,and the degree of marsh landscape fragmentation is higher.The indexes of aroma diversity and evenness were decreasing,and the landscape distribution was developing towards equilibrium.Grassland area was significantly positively correlated with precipitation and average temperature,grassland,farmland,marsh and water area were negatively correlated with the number of sheep.(2)Based on watershed SEBAL model,the amount of evapotranspiration(ET)and land surface temperature(LST)simulated values and measured values are more close to the surface net radiation(Rn)and soil heat flux overvalued(G)inversion values to a certain extent,the SEBAL model of anti easy-restoration degree basin upstream transpiration quantity simulation effect is good,has the feasibility.The low values of surface parameters NDVI and Rn in the study area are located in the northwest,while the high values are located in the southeast and south of the study area.The surface Albedo,LST and G increased from southeast to northwest.(3)ET has a significant seasonal variation and presents a spatial trend of high in the east and low in the west.ET in the marsh and wetland remains at a high level in the growing season,and the maximum ET in the study area can reach 10.32mm·d-1.ET was significantly correlated with Albedo,LST,NDVI and Rn,and the correlation between ET and table parameters in different years was roughly the same.The order of correlation between meteorological factors and ET was:Rn?Tmax?T min?VPD?RH?WS.From 2015 to 2017,the daily evapotranspiration of water bodies and marshes was relatively large,followed by cultivated land.The daily evapotranspiration of cultivated land in summer was close to that of river valley wetland,ranging from 3.8 to 8mm,and the evapotranspiration of grassland varied from 0.5 to 4.3mm.Evapotranspiration of different land use types ranged from large to small:water body?marshland?cultivated land?grassland?others.