Abstract
Estimating the effects of large scale afforestation is essential for the accurate understanding of its potential for the mitigation of climate warming. We used satellite observations to quantify the effects of the conversion of open lands (i.e., grassland and cropland) and natural forests to plantation forests and their associated biophysical processes (i.e., albedo and evapotranspiration (ET)) on land surface temperature (LST) in Guangdong Province, China. The hypothetical change (mean 2002–2018 values of LST difference between plantation forests and nearby lands in 2010) using the moving window searching-based method and actual change (changes of afforested area affecting the LST difference from 2000 to 2010) using the spatial pattern change trend method were detected in order to characterize the spatiotemporal variations in surface temperature, related albedo, and ET. The relationships between albedo, ET, and surface temperature change were also determined in combination with interpolated air temperature and precipitation. Results showed that the two methods-based afforestation changes had a similar net cooling effect, but a discrepancy in diurnal, seasonal, and spatial variations occurred. Overall, the actual change of afforested area led to a cooling effect by an average of −0.18 ± 0.02 °C, especially from croplands, which was greater than the air temperature. Individually, afforestation in the mid-subtropical forest zone (north of 24 °N, northern Guangdong) had a warming effect, especially during the transition from natural forests to plantation forests. We also observed an increase in cooling for the tropical forest zone across latitudes. Warming during the dry season was triggered by the albedo from plantation forests, but the albedo-induced forest cover change impacts on LST were quite complex. Meanwhile, ET dominated the cooling during the wet season and warm season. Additionally, enhanced precipitation played a more prominent role in the ET-induced cooling. Evaluation of the effect of temperature change induced by afforestation illustrates the importance of protecting natural forests and avoiding extensive artificial afforestation, especially in northern Guangdong Province, and reverting agricultural land to forest, especially in western Guangdong Province. This analysis also provides a basis for feedback from forest management activities to climate change in southern China.
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