Impacts of afforestation on land surface temperature in different regions of China

To assess the impacts of afforestation on land surface temperature (LST) in China and provide a basis for future afforestation and warming mitigation policies, adjacent forest and open land are compared using ten years of satellite data. Most regions in China exhibit a diurnal asymmetry in the magnitude and sign of the effects of afforestation, with daytime cooling and nighttime warming. Afforestation has annual daily cooling effects in most regions of China because the magnitude of annual nighttime warming is generally weaker than that of the annual daytime cooling. We attributed the warming and cooling effects of afforestation to the changes of evapotranspiration (ET) and albedo. The annual average albedo of forest is smaller than that of open land, and the albedo differences between forest and open land vary spatially, with larger differences in places with snow cover. In the annual average, ET over forest is greater than that over open land, with the largest values in the southern of Yangtze River. The daytime differences in LST between forest and open land are driven by the cooling effects of ET and warming effects of albedo, and the cooling effects of ET dominate. The nighttime warming effects of afforestation is related with the release of the energy stored in the soil during daytime. Evergreen broadleaf forest and deciduous broadleaf forest are recommended as the choice of afforestation in south and in north of the Yangtze River respectively to decrease the LST if the afforestation program in China is to be expanded.