Response Of Land Use Change To Urban Evapotranspiration And Surface Temperature

In the late 1970s,China began to enter the urbanization.By the end of 2017,the urbanization rate of China reached 61.55%.With the development of urbanization,there are also many problems,such as traffic congestion,housing shortage,employment difficulties and other social problems,heat island effect,soil pollution,water quality deterioration and other environmental problems.In this study,the main urban area of Shenyang was taken as the research object,and the effects of land use/cover types on surface temperature and ET were analyzed,which could provide reference for urban ecological construction.The main research results are as follows:(1)The accuracy of land use/cover type is evaluated by establishing confusion matrix.The overall classification accuracy is above 89%,and the Kappa coefficient is above 0.84,which is highly consistent and meets the classification requirements.By establishing the transfer matrix of land use/cover type,2.10 million hectares of woodland were transferred from 2001 to 2017 in the main urban area of Shenyang,with a total of 2.19 million hectares of arable land being converted into arable land.Ten thousand hectares have been transferred,mainly to woodland;water has been transferred from 0.49 million hectares,mainly to arable land;construction land has been transferred from 10.27 million hectares,mainly to arable land;grassland has been transferred from 0.45 million hectares,mainly to arable land.(2)The atmospheric correction method is used to retrieve the surface temperature.According to the verification of the meteorological station monitoring data,the retrieved surface temperature has high accuracy and meets the research needs.There are obvious urban heat island phenomena in Shenyang.Overall,the surface temperature continued to rise from2001 to 2017,and the low value area of ground temperature gradually decreased.In 2017,about one third of the areas showed high temperature distribution,and the ground temperature exceeded 30 C.In 2001,the high temperature area was concentrated in the central urban area.In 2005-2013,the five districts of Dadong District,Huanggu District,Shenhe District,Heping District and Tiexi District in the central city were still in high temperature areas,while the low temperature values of other counties were lower than those in 2001.Compared with 2001,the area of high temperature increased,the range of temperature increase in Hunnan area and Yuhong area was more obvious,and the high temperature patches in Hunnan area and Yuhong area increased more.(3)According to SEBS model,the ET of Shenyang main urban area is retrieved.The accuracy of the retrieved data is verified by R~2=0.8918 with the observation results of meteorological stations,which shows that the simulation results are of high accuracy.The daily ET in Shenyang's main urban area tends to be low in the middle and high around the city.The low-value areas are mainly urban construction land,and the high-value areas are mainly woodland in the northeast.The low-value areas of daily ET increase and decrease in time,and the high-value areas of daily ET diffuse outward with the increase of cultivated land area.(4)By using the regional analysis function of ArcGIS software,the mean surface temperature of different land use/cover types is calculated.The highest mean surface temperature is for construction land,and the lowest mean surface temperature is for forest land and water body.At the same time,NDVI,NDWI,NDBI index and surface temperature(LST)were analyzed.NDVI,NDWI and LST were negatively correlated,NDBI and LST were positively correlated,indicating that vegetation and water had a certain mitigation effect on urban heat island,and the spread of construction land would aggravate the phenomenon of urban heat island.Multivariate regression models between surface temperature and NDVI,NDWI and NDBI were established.The relative errors of surface temperature in 2016 and2018 were 6.6%and 8.96%,respectively.The model has good effect.(5)Using the regional analysis function of ArcGIS software,the daily ET of different land use/cover types was counted.The daily ET of construction land was the smallest,and the daily ET of water body and forest land was the largest.The average daily ET of different land use/cover types increased with the increase of water content and vegetation coverage.For different surface parameters,the average size of vegetation index is NDVI<SAVI<LAI,and the average size of water body index is NDWI<MNDWI.NDVI,SAVI,LAI,NDWI,MNDWI,LST and daily ET have a high correlation in the study period,among which NDVI,SAVI,LAI,LST and daily ET have a positive correlation,NDWI,MNDWI and daily ET have a negative correlation.Multivariate regression model between daily ET and NDVI,NDWI,LST was established.The relative errors of ET in 2016 and 2018 were 9.1%and 8.8%,respectively.The model has good effect.