黄土高原植被恢复对地表的冷却作用及变化规律

Cooling Effect Induced by Afforestation on the Loess Plateau and Its Change Law

基于黄土高原的土地覆盖类型数据,并结合MODIS地表温度、反照率和蒸散发数据产品以及降水数据,分析了该区域2002—2015年间造林对地表温度的影响,并进一步分析蒸散发和反射率的驱动作用。结果表明:研究期间黄土高原造林区域地表温度的变化主要由白天地表温度变化主导而表现为降温((-0.78±1.25)℃),且主要是蒸散发增加((0.84±1.35)mm/d)所驱动。造林引起的地表温度变化与降水梯度密切相关,在半干旱区(年均降水量<400 mm)造林会引起微弱的增温((0.03±0.22)℃)。此外,该区域由造林引起的地表温度变化呈现季节性规律,即春季及夏季的降温程度较大,而冬季降温作用微弱。春季白天地表降温最强,其次是夏季,秋冬季节降温较弱;而对于夜间温度,冬季增温强烈,其次为春季,秋季及夏季。地表温度变化与地表反照率和蒸散发变化之间相关性显示,蒸散发冷却效应抵消了反照率引起的暖化效应,主导白天地表温度变化。而夜间暖化现象在一定程度反映白天热储量释放。黄土高原植被恢复对地表具有冷却效应,在区域尺度上减缓了气候变暖的趋势。

The purpose of this article was to analyze the impacts of afforestation in different regions and seasons on the Loess Plateau on the land surface temperature(LST)from 2002 to 2015 and their driving factors(Albedo and evapotranspiration)based on MODIS land cover,LST,Albedo,evapotranspiration(ET)data products and precipitation data.The results showed that during the study period,the cooling effect in the daytime dominated LST change((-0.78±1.25)℃)and the cooling effect was mainly driven by ET((0.84±1.35)mm/d).Moreover,the land surface temperature change caused by afforestation was closely related to precipitation,and afforestation would cause a slight warming((0.03±0.22)℃)in semi-arid regions where the mean annual precipitation was less than 400 mm.In addition,the variations of LST presented a seasonal pattern,that was,the observed cooling effect in spring and summer was greater,while in winter,this effect was weak.The daytime cooling effect was the strongest in spring,followed by summer,winter and autumn.In terms of the nighttime LST,the warming effect in winter was the strongest,followed by spring,autumn and summer.Meanwhile,the correlation between LST variations and ET change(Albedo change)showed that the cooling effect derived by ET offset the warming effect caused by albedo and dominated the daytime LST variations.Such warming impact at night reflected that storage heat during the day was likely to be released at night.Vegetation restoration on the Loess Plateau had a cooling effect,which slowed down the trend of climate warming on a regional scale.