Temporal And Spatial Evolution Of Evapotranspiration And Its Influencing Factors In Daling River Basin Of Chaoyang City

Evapotranspiration is a key component of the thermal balance of surface waters.Under the influence of global climate and land cover changes,accurate estimation of surface evapotranspiration and investigation of the variation patterns and influencing factors of surface evapotranspiration are of great research significance for regional ecological environment protection and comprehensive water resources management.As the largest river in western Liaoning Province,the Daling River has fragile water resources and ecological environment.Over the past two decades,the land cover types in the Daling River Basin of Chaoyang City have undergone significant changes.In this paper,the supervised classification method of support vector machine is used to extract the land cover type information of Chaoyang section in Daling River Basin。 The evolution characteristics and changing patterns of surface cover types in the Daling River Basin from 2000 to 2020 are analysed using methods such as land change transfer matrix.The remote sensing evapotranspiration data in the Daling River Basin of Chaoyang City are statistically processed based on the mean method,the coefficient of variation method and the least squares method using the Penman-Monteith evapotranspiration model of the Moderate Resolution Imaging Spectroradiometer.The spatio-temporal variation patterns of surface evapotranspiration in the Daling River Basin of Chaoyang City over twenty years are analysed at annual,seasonal and monthly scales.Finally,correlation analysis,variance analysis and non-parametric tests are used to analyse the correlation between climate change,surface cover types and surface evapotranspiration in the Daling River Basin of Chaoyang City.Based on remote sensing technology and statistical methods,the evapotranspiration under the influence of climate change and land cover change was evaluated and improved comprehensively and systematically.The main conclusions of the research are as follows:(1)The changes in land cover types in the Daling River Basin of Chaoyang City are very significant.The largest land cover type is cultivated land,which shows an overall trend of first decreasing and then increasing.Forest and cropland show an opposite changing relationship,with forest area showing a slow increasing trend.The area of grassland is decreasing year by year and shows a downward trend.The area of water bodies and built-up areas increases from year to year,with water bodies showing a fluctuating upward trend and built-up areas showing a stable upward trend.The total area of unused land remains almost unchanged,showing an overall trend of first decreasing and then increasing,with the same changing trend as that of cultivated land.(2)The transfer of land cover types in the Daling River Basin of Chaoyang City is mainly dominated by cultivated land,forest and grassland.The largest transfer-out type is grassland,which is mainly transformed into forest,and the transfer occurs in all counties and districts.The largest transfer-in type is arable land,which mainly transfers to forest,and the transfer occurs in all counties and districts.Forests are mainly transferred to cropland,and the transfer occurs in all counties and districts.The transfer trends of other types remain basically unchanged,showing a process of change from unused land to construction land to water bodies to cultivated land.The area of the Daling River basin remains basically stable.(3)In terms of interannual changes,the total surface evapotranspiration shows a fluctuating upward trend,with uneven distribution and a wide range of fluctuation.The spatial distribution generally shows a characteristic of high upstream and low downstream.Seasonal differences in surface evapotranspiration are significant,with an overall normal unimodal distribution,with a spatial distribution similar to interannual changes,and evapotranspiration changes are more pronounced in the middle reaches of the basin.Evapotranspiration is lowest in winter and highest in summer,with a fluctuating upward trend in June and July,a fluctuating downward trend in August,and a decreasing rate of change from month to month,with evapotranspiration gradually stabilising.The overall spatial distribution is the same as the interannual changes,with more pronounced evapotranspiration changes in the upstream basin.(4)Surface evapotranspiration in the Daling River basin of Chaoyang City is influenced by various factors,with temperature,humidity and vegetation cover having the most significant effects.The influence of temperature on surface evapotranspiration shows a moderate positive correlation,while the influence of vegetation cover and humidity shows a moderate negative correlation.The ability to influence is highest for vegetation cover,followed by temperature,and humidity has a relatively small influence.At the same time,there is a certain correlation between the influencing factors,with temperature and wind speed,precipitation and humidity,and unused land and vegetation cover all showing a significant positive correlation and a mutually reinforcing effect.