| Land surface temperature is an important component of the energy transport link between the land and the atmosphere and has a strong influence on the development of terrestrial ecosystems.Changes in land surface temperature lead to changes in evapotranspiration,air temperature,precipitation,soil moisture and vegetation,which contribute to changes in the material and energy balance between the land and the atmosphere,thus causing the evolution of regional ecohydrological processes.The analysis of the spatial and temporal changes of land surface temperature in the watershed and its influencing factors can help to deeply understand the surface water-thermal conversion mechanism,which is of great significance to the ecohydrological study of the watershed.Using the Liuchong River basin in Guizhou as the study area,the paper uses Mann-Kendall trend test,Theil-Sen slope estimation,spatial autocorrelation and geographic probe to study the spatial and temporal variation of land surface temperature and its influencing factors in the Liuchong River basin,with a view to providing a reference for studying the ecohydrological evolution of the basin.The main conclusions are as follows:(1)From 2000 to 2020,the land surface temperature of the Liuchong River basin changed significantly.At the monthly scale,the land surface temperature showed a fluctuating decreasing trend in all months except June,with significant decreasing trends in January,February,September,November and December.At the seasonal scale,the land surface temperature changes all showed a decreasing trend,and the change rate showed a trend of winter > autumn > spring > summer,among which the changes in spring,autumn and winter were significant.At the annual scale,the land surface temperature changes showed a significant decreasing trend with a rate of change of-0.0975°C/a.The land surface temperature changed abruptly in 2003.The rate of change before the abrupt change was-0.3353℃/a,and the rate of change after the abrupt change was-0.0236℃/a.(2)The spatial distribution of land surface temperature in the Liuchong River basin was uneven,and the distribution areas of low-temperature and lower-temperature zones were the largest and smallest in 2000-2020 and before and after the abrupt change,and the proportion of the distribution areas of low-temperature zones were51.88%,51.17% and 52.35% in 2000-2020 and before and after the abrupt change,respectively,and the distribution areas of lower-temperature zones were 5.43%,5.80% and 5.24 in 2000-2020.The land surface temperature Moran index was 0.908,0.885 and 0.909 in2000-2020 and before and after the mutation,respectively,with significant spatial aggregation characteristics,and the aggregation types of local spatial autocorrelation were mainly high-high and low-low;the land surface temperature standard deviation ellipse distribution direction was generally northwest-southeast.After the mutation in 2003,the distribution of high temperature,lower temperature,medium temperature,and higher temperature regions became more dispersed,and the spatial distribution of low temperature regions became more concentrated;The directionality of low temperature zone,lower temperature zone,middle temperature zone and higher temperature zone is more and more obvious,but the overall centripetal force is weakening.(3)The characteristics of land surface temperature changes in different climatic zones of the Liuchong River Basin are different,and the influencing factors are also different.The Liuchong River Basin can be divided into three climate types: alpine climate zone,warm and cool climate zone,and mild climate zone.Among them,the land surface temperature of the mild climate zone is the highest and the warming rate is fast;the land surface temperature of the cool climate zone is lower than that of the mild climate zone and the temperature changes are more stable;the land surface temperature of the alpine climate zone is the lowest and the cooling rate is faster.On the monthly scale,there is a significant correlation between the changes of temperature and precipitation and land surface temperature in all three climate zones,and the significant correlation between land surface temperature and temperature is more obvious in the mild climate zone,and the relationship between temperature and land surface temperature is more significant in the moderate climate zone.At the seasonal scale,the changes of air temperature and land surface temperature are positively correlated and precipitation is negatively correlated in warm and cool climate zones,and the correlation of precipitation is stronger;the land surface temperature is not significantly affected by meteorological factors in mild climate zones.At the annual scale,land surface temperature in the warm-cool climate zone and alpine climate zone is not influenced by a single factor,and land surface temperature in the mild climate zone is positively influenced by grass and negatively influenced by water bodies,and there are significant correlations among some influencing factors in the three types of areas,and the interaction makes land surface temperature changes less influenced by a single factor and mainly influenced by the combination of multiple factors.(4)By analyzing the spatial distribution of temperature and precipitation before and after the abrupt change,it is found that the climate in the Liuchong River basin gradually warms and dries up,affecting the surface energy balance.By increasing the total net radiation and decreasing the long-wave downward radiation at the surface,it leads to the gradual decrease of surface sensible heat flux and soil heat flux,and the decrease of net radiation flux at the surface,resulting in the change of the distribution ratio of surface heat.The difference of land surface temperature under the influence of climate warming and drying leads to the change of surface water-heat combination,which affects the yield of cool-loving crops and crops in rain-fed agricultural areas to some extent,will cause the change of sowing period of crops in each season,and leads to the extension of crop planting area to higher altitude areas.(5)Before the mutation,the area of negative correlation between air temperature and vegetation NPP and land surface temperature in the Liuchong River basin was widely distributed;the fluctuation of land surface temperature was the least in water bodies and the greatest in grasslands,and after the mutation,the area of positive correlation between air temperature and vegetation NPP and land surface temperature increased,and the positive effect of air temperature on land surface temperature change and the negative effect of vegetation NPP were more obvious;the fluctuation was the least in impervious surfaces and the shrubs and grasslands fluctuations were the largest.The effect of precipitation on land surface temperature in the watershed was small both before and after the mutation;altitude and land surface temperature were negatively correlated,with the strongest effect on land surface temperature change in high and middle mountainous areas.The effect of interaction between factors on land surface temperature was more obvious after the mutation,and air temperature was the most important influence on land surface temperature before and after the mutation,with q-values of 0.47 and 0.52 before and after the mutation,respectively.The influence of vegetation NPP on land surface temperature increased substantially after the mutation.It may be related to the recovery of vegetation over a large area of the watershed.After the mutation,the vegetation cover increased and the coupling effect of temperature and vegetation evaporation was stronger,leading to a decrease in downward long-wave radiation,which decreased the land surface temperature.The results of the study analyze the characteristics of land surface temperature changes and the degree of influence of each factor at different temporal and spatial scales,with a view to providing some theoretical references for the benign cycle of surface water-heat and the healthy and sustainable development of ecosystem conservation in the Liuchong River basin. |
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