不同气候带退耕还林对区域气温的影响差异分析

退耕还林改变陆表覆盖状况,导致碳收支和地表能量平衡变化,从而影响区域气温。论文通过定量估算耕地转为林地导致生态系统吸收大气CO₂和地表能量平衡的变化,分析21世纪初10 a中国不同气候区开展退耕还林对区域气候调节的影响差异。结果表明：1）仅考虑碳调节,各气候区退耕还林皆表现为241.6~470.2 Mg CO₂-eq hm^-2的碳蓄积过程,具有2.2~16.5 Mg CO₂-eq hm^-2的碳汇作用即致冷效应,特别是亚热带湿润区。2）仅考虑地表能量平衡,中温带干旱与半干旱区退耕还林引起的净辐射增加程度大于潜热通量的增加程度,因此地表对大气供热表现为增温效应;而亚热带湿润区退耕还林引起净辐射减少及潜热通量增加,青藏高原、中温带湿润区净辐射增加程度小于潜热通量的增加程度,因此地表对大气供热皆表现为致冷效应。3）同时考虑碳调节和地表能量收支,中国亚热带湿润区退耕还林的致冷效应是仅考虑碳调节致冷效应的1.25~1.45倍,而中温带干旱区退耕还林的致冷效应则为仅考虑碳调节效应的近一半。

Impacts of Returning Farmland to Forest on Regional Air Temperature in Different Climatic Zones

Land use and land cover change influences regional climate through both biogeochemical and biogeophysical processes. Afforestation has been one of the most intensive human activities on land cover. It results in the increase of carbon sequestration and has been proposed as a most effective strategy to mitigate climate change. However, considering only carbon storage would lead to underestimation or overestimation of the impact of afforestation on climate regulation. This paper aimed to disclose the impacts of returning farmland to forest on regional temperature by the carbon budget and surface energy balance in different climatic zones. The results showed that if only the carbon regulation effect was considered, the returning farmland to forest was in the carbon sequestration process with 241.6-470.2 Mg CO₂-eq hm^-2, and was carbon sinks of 2.2-16.5 Mg CO₂-eq hm^-2 in various climate zones, which means the cooling effect on air temperature, especially in subtropical and humid regions. If only the biophysical process was considered, the returning farmland to forest in northern arid and semiarid regions resulted in more increase in net radiation than increase in latent heat flux, so the returning farmland to forest had warming effect on temperature. However, it resulted in decreased net radiation and increased latent heat flux in southern subtropical regions, and less increase in net radiation than increase in latent heat flux in Tibetan Plateau and temperate humid regions, so the returning farmland to forest had cooling effects on temperature in those regions. Therefore, when taking into account both the carbon regulation and land surface energy balance, the cooling effects of the returning farmland to forest in southern subtropical regions is 1.25 to 1.45 times more than that when only the carbon regulation was considered, while the cooling effects in northern arid and semiarid regions is about half of that when only the carbon regulation was considered