北方典型农牧交错带草地开垦对地表辐射收支与水热平衡的影响

以北方典型农牧交错带草原和农田生态系统的涡度相关数据为基础,对比分析了生长季两种不同土地利用类型的辐射和水热通量之异同,揭示了草地开垦影响地表辐射收支与水热平衡的机制。结果表明:在植被生长季(5月—9月),草地开垦引起太阳总辐射增加了10.74%,短波反射辐射减少了14.20%,净辐射增加了35.16%;在水热通量方面,草地开垦引起潜热通量日积分平均值增加了0.20MJ/m~2,同时显热通量减少了0.09 MJ/m~2;生长季内地表反照率减小,表征地表吸收太阳辐射增加,有升高气温的趋势;非生长季内地表反照率增加,有降低气温趋势,此外地表反照率与土壤湿度存在负指数关系;波文比在植被生长早期和末期增加,生长旺期减小,说明草地开垦与影响着近地表大气状态,从而改变了区域气候。

Impacts of grassland reclamation on land surface radiation and water-heat fluxes in the farming-pastoral ecotone of northern China

We compared land surface radiation and water-heat flux of two different land use types using eddy covariance flux data of typical grassland and cropland ecosystems in a farming-pastoral ecotone of northern China. The comparisons revealed that the biophysical mechanisms of grassland reclamation affected the surface radiation flux budget and the water-heat flux balance. The results further showed that, during the growing season (May-September), grassland reclamation increased the solar radiation by 10.74%, reduced the shortwave reflected radiation by 14.20%, and increased the net radiation by 35.16%. As for the water-heat flux, grassland reclamation increased the latent heat flux 0.20 MJ/m², whereas the sensible heat flux was reduced by 0.09 MJ/m². The surface albedo decreased during the growing season, which was illustrated by the surface that absorbed more solar radiation and had a tendency to rise in the temperature. In contrast, the albedo increased during non-growing season, which was illustrated by a decrease in the temperature; in addition, a negative exponential relationship between surface albedo and soil moisture was observed. The Bowen ratio in the early and late vegetation growth period increased and decreased dramatically during these growing stages. Finally, the grassland reclamation affected the near-surface atmospheric conditions, which consequently changed the regional climate.