Impact Of Vegetation Greening On Temperature Change In Arid And Semi-arid Regions In The Northern Hemisphere

The arid and semi-arid regions are one of the most sensitive and vulnerable regions in the process of global warming,and their warming rate is much higher than other regions,especially in winter,which is called a significant warming phenomenon in winter.The CMIP5 multi-model unanimously predicts that the arid and semi-arid regions will continue to expand in the 21 st century,which is related to the lives of billions of residents and the vital interests of many developing countries.However,at the same time,global vegetation has shown a tendency to turn green.Whether the vegetation turns green will affect the temperature change in arid and semi-arid areas,and the mechanism has not yet been cleared.Through the observation data and satellite remote sensing data,this paper analyzes the effect of vegetation greening on the temperature change trend in arid and semi-arid areas.The study found that vegetation greening and significant temperature increase occur at the same time,and they are most significant in the high latitudes of the northern hemisphere.Taking this as an entry point,this paper analyzes the types of underlying surfaces corresponding to vegetation greening and significant temperature increase,and then analyzes the changes in transpiration and albedo caused by vegetation greening,and their effects on surface temperature in winter and summer.Finally,the two-dimensional energy balance model is used to discuss the long-term effects of high-latitude vegetation turning green on the mid-latitude desert belt evolution.The main conclusions include the following:(1)Based on CRU reanalysis data,GIMMS LAI3 g data,MODIS landcover data,etc.,the global temperature change trend,drought index,leaf area index(LAI),land use type distribution from 1982 to 2014 were analyzed,and the results showed that The total arid and semi-arid area of the world accounts for 41% of the global land area.Among these four types,the semi-arid area has the largest area,accounting for about one third of the entire arid and semi-arid area;the Northern Hemisphere has increased significantly from 1982 to 2014 The higher the temperature,the greater the drought index,and the more obvious the trend of temperature increase.From 1982 to 2014,there was a global phenomenon of vegetation turning green.The larger the drought index,the greater the degree of local humidification,and the more obvious the vegetation turned green.Deciduous coniferous forests,evergreen deciduous forests and evergreen coniferous forests have the most obvious greening tendency.These forests are mainly distributed in the northern hemisphere with the highest temperature increase.(2)Based on GIMMS LAI3 g data,MODIS albedo data,CERES solar radiation data,etc.,using a multiple linear regression model,quantitatively analyzed the contribution of global vegetation greening to surface temperature changes from 1982 to 2014.From the perspective of the response change of albedo,the effect of vegetation greening on the surface temperature in winter and summer was further analyzed,so as to obtain the comprehensive effect of vegetation greening on seasonal temperature difference.Studies have shown that during the period of global warming,LAI has been increasing,especially in high latitudes;the greening of vegetation has caused an increase in transpiration and reduced albedo,but the combined effects of the two effects in winter and summer are different.In summer,the transpiration cooling effect caused by the greening of the vegetation is stronger,and the surface temperature appears to be cooling.In winter,the albedo warming effect caused by the greening of the vegetation is stronger,and the surface temperature is warming;therefore,the vegetation caused by the greening The difference in seasonal warming in most areas of the middle and high latitudes in the northern hemisphere is reduced,that is,the local effect caused by the vegetation turning green is to reduce the seasonal warming difference.(3)Evidence from satellite remote sensing indicates that there is widespread vegetation greening at high latitudes in the northern hemisphere.Large-scale ecosystem changes may cause global responses.This paper focuses on whether arid and semi-arid areas,especially the desert belts in the middle latitudes,will be affected by the vegetation turning green at high latitudes.For the first time,a two-dimensional energy balance model was used to study the impact of greening in high-latitude regions on mid-latitude deserts.It was found that when greening occurs in high-latitude regions,the mid-latitude desert recedes at the southern boundary,while the polar ice belt and low-latitude vegetation belt are expanding,meaning that high-latitude vegetation turning green may inhibit the expansion of the mid-latitude desert belt.