Land Surface Temperature Effect And Its Attribution Analysis Of Afforestation In China

Forest cover change can cause strong local biophysical feedback on climate.Satellite observations of land surface temperature（T）and land cover distribution or forest cover change have been widely used to examine the effects of afforestation/deforestation on local surface temperature change（ΔT）.However,different approaches were used by previous analyses to quantify ΔT,and it remains unclear whether the results of ΔT by these approaches are comparable.Since 1999,China has implemented massive afforestation projects and can serve as an ideal case to compare ΔT caused by afforestation quantified by these different approaches.Therefore,this research identified three approaches,namely the "space and time","space for time",and singular value decomposition method to quantifying actual ΔT（ΔT_a）,mixed potential ΔT(ΔT_p1) and complete potential ΔT(ΔT_p2) based on multiple satellite observations（Global Forest Change,MCD12Q1,Globe Land30）,respectively.We explored the cause of difference of the three effects.At the same time,based on these three effects,we revealed the zonal pattern and seasonal pattern of the impact of afforestation on land surface temperature,as well as the characteristics of changes with precipitation.We explored the driving biophysical factors of ΔT differences caused by afforestation and the corresponding changes in energy exchange combined with albedo（α）,evapotranspiration （ET） and radiation data.To understand the effect of different afforestation types on land surface temperature and guide the practice of afforestation,this study discussed forest types on land surface temperature and biophysical factors further.The main conclusions are as follows:（1）The magnitude of ΔT_a（-0.12±0.57℃） induced by afforestation is significantly lower than ΔT_p1（-0.60±1.36℃）and ΔT_p2（-0.86±1.62℃）,and increases with afforestation fraction（Faff）.When ΔTa is extended to a hypothetical case that Faff reaches 100%,ΔT100%a（-0.62±0.05℃）is comparable to ΔT_p1 or ΔT_p2.（2）Afforestation strongly cools the surface,which is dominated by daytime surface temperature change driven by evapotranspiration.（3）The effect of afforestation on land surface temperature showed obvious seasonal differences.Afforestation causes the strongest surface cooling effect in summer,slightly weaker cooling degree in spring and warming effect in winter.In spring and summer,the ΔET caused by afforestation is stronger,leading a cooling effect.Strong albedo changes and weak ET changes causes the slightly warming effect in winter in this area.（4）There is an obvious latitude pattern on the change of land surface temperature caused by afforestation.The decrease degree of albedo caused by afforestation with latitude escalating rate was stronger,which led to the stronger warming effect of afforestation on high latitude areas.The contribution of summer evapotranspiration to annual evapotranspiration is the largest,and it decreases with increasing latitude.As a result,the cooling effect of afforestation on low latitude areas is the more obvious.（5）The change of land surface temperature caused by afforestation is closely related to precipitation.The cooling effect of afforestation increased with the rise in precipitation.In the semi-arid area where the annual average precipitation is lower than 400 mm,afforestation causes slight warming.Subhumid and humid areas（annual precipitation >400 mm）present an obvious cooling effect.Δα drives the warming of land surface temperature in arid regions,while the cooling of land surface temperature in humid regions is mainly controlled by evapotranspiration.