三北工程黄土高原丘陵沟壑区森林降温增湿效果研究

The cooling and humidifying effect by the forest ecosystem in the hilly and gully area of Loess Plateau of the Three North Shelter Forest System Project region

生态系统可通过植被蒸腾与土壤蒸发作用调节区域温度与湿度。三北工程黄土高原丘陵沟壑区属于干旱和半干旱区,森林降温增湿功能有助于改善区域生存环境。在分析研究区森林覆被变化基础上,利用Penman-Monteith公式模拟了森林实际蒸散量,研究了森林增湿与降温效果。研究结果显示:(1)1980-2015年研究区森林面积增加了2.25%,主要来自荒草地、耕地和荒漠;(2)1980-2015年研究区森林6-9月实际蒸散总量为1.19×1010-1.40×1010 t/a,平均实际蒸散量为219-257 mm,可使区域6-9月绝对湿度每日增加0.47-0.55 g/m3,相对湿度每日增加2.87%-3.32%;(3)森林通过蒸散作用吸热量为29.15×1015-34.26×1015 kJ/a,单位面积蒸散吸热量为53.72×108-63.13×108 kJ hm-2 a-1,通过蒸散吸热日降温量为0.92-1.08℃/d;(4)研究区森林蒸散量在1980-2010年逐渐增加,但在2015年明显下降,这主要是由降水减少导致;森林面积较大的山西和陕西森林蒸散降温增湿效果较好。通过对比相同年份不同土地覆被发现,森林实际蒸散量显著高于其他土地覆被类型。因此,未来研究区可在水资源承载能力范围内适当增加森林面积,充分发挥森林调节区域气候的作用。

The ecosystem can regulate regional temperature and humidity through evapotranspiration. The climate in the hilly and gully area of the Loess Plateau in the Three North Shelter Forest System Project(TNSFSP) region is arid and semi-arid, and the cooling and humidifying function of the forest ecosystem is crucial for improving the living environment in this region. Based on the analysis of forest cover changes in this area, in this study, we simulated using the Penman-Monteith formula and investigated the contribution of evapotranspiration by ecosystems to regional climate regulation. The results show that:(1) The forest area in the study region(mainly grassland, cropland, and desert) increased by 2.25% from 1980 to 2015.(2) The total amount of forest actual evapotranspiration(AET) in the study area from 1980 to 2015 was between 1.19 × 1010 t/a and 1.40 × 1010 t/a, and average AET ranged from 219 mm to 257 mm. Absolute humidity from June to September in 1980 to 2015 increased by 0.47-0.55 g/m3 per day, and the relative humidity will increase by 2.87%-3.32% per day.(3) Heat absorption of the forest through evapotranspiration was estimated as 29.15 × 1015 to 34.26 × 1015 kJ/a, evapotranspiration per hectare was 53.72 × 108-63.13 × 108 kJ hm-2 a-1), and the daily cooling rate by evapotranspiration was 0.92-1.08 ℃ d-1.(4) The amount of forest evapotranspiration increased gradually from 1980 to 2010, but it decreased significantly in 2015, which was mainly caused by the decrease in precipitation. Spatially, forests in Shanxi and Shaanxi provinces, with a larger forest area, had better evapotranspiration and humidification effects. Comparison of the different land cover in 1980 to 2015 showed that the actual evapotranspiration of the forest was still significantly higher than other land cover types. In future, the forest area will be appropriately increased within the carrying capacity of water resources, and the role of forest will be even more crucial in regional climate regulation.