Satellite observations have shown an evident trend of vegetation greening in China since the 21st century. Vegetation change can impact the momentum, energy and water exchange between land surface and atmosphere by altering surface properties such as albedo and roughness, thereby influencing regional climate. However, the biophysical effects of vegetation changes on near-surface air temperature (SAT) remain elusive because prior studies focused more on land surface temperature (LST). SAT is more relevant to climate mitigation and adaptation, as this temperature is experienced by humans. Moreover, SAT is also a widely used metrics to define hot extremes.
Recently, the team of Assistant Prof. Jun Ge and Prof. Weidong Guo investigates and quantifies the impact of vegetation greening on SAT and hot extremes in China since the 21st century by using the “space-for-time” method based on two sets of high-resolution climate datasets and satellite observations. It is found that the greening vegetation causes a decrease in SAT in most parts of eastern China. The arid/semi-arid areas and the climate transitional zone in northern China are the most sensitive regions to vegetation greening. For instance, an increase of one unit of leaf area index (LAI) can cause a cooling of more than 1°C of SAT in the northern Loess Plateau and Inner Mongolia. Meanwhile, vegetation in arid/semi-arid regions could induce an additional cooling effect under extreme hot days.
The study illuminates that the physical mechanisms of SAT response to LAI change. Although the greening vegetation in the China would cause warming by decreasing surface albedo, the concomitant increase in surface roughness and latent heat would have a cooling effect, resulting in an overall cooling effect. In arid/semi-arid areas, the cooling effect is caused by the enhanced latent heat. In the humid area, on the other hand, the cooling effect is dominated by the increase of surface roughness due to greening vegetation. Latent heat is closely related to the transpiration of vegetation, which is more sensitive to temperature changes. This may explain why increasing vegetation in arid/semi-arid regions exhibits stronger cooling effects on hotter days.
This study reveals that the greening vegetation in China over the past 20 years can slow down the SAT warming. The restoration of vegetation in arid/semi-arid regions could also bring additional climate benefits in mitigating extreme heat events. This study provides new insights into the climate benefits of vegetation greening. This study is published as Greening vegetation cools mean and extreme near-surface air temperature in China in Environmental Research Letter. The first author of the paper is PhD student Yipeng Cao, and the corresponding authors are Assistant Prof. Jun Ge and Prof. Weidong Guo. Other co-authors include PhD student Yu Liu, master students Xing Luo, Limei Yang, and Chaorong Chen (currently working at Qinghai University of Science and Technology). This study is jointly supported by the National Natural Science Foundation of China (42130602, 42375115, 42005096), Jiangsu Collaborative Innovation Center for Climate Change, and Frontiers Science Center for Critical Earth Material Cycling of Nanjing University.