土地覆被变化过程中叶面积指数与降水量对地表能量平衡的贡献——基于SiB2的模拟结果

土地覆被变化过程中,叶面积指数(LAI)是地表能量平衡重要的影响因素,且与降水等多种因素存在交互作用。以2003年中国东北地区农田、森林和草地三种覆被类型和三种LAI月变化过程为研究对象,着重分离出土地覆被变化过程中LAI对地表能量平衡的作用,认清覆被和LAI变化对地表能量平衡的相对作用。利用SiB2模型研究不同降水条件下土地覆被和LAI变化对地表能量平衡的影响。结果表明:①覆被变化对净辐射的影响最大,年均14.5W?m-2左右。②LAI主要改变净辐射对潜热和显热的分配,对农田和草地而言,LAI增加明显提高(减小)潜热(显热)分配比例;对森林而言,LAI对潜热和显热分配的影响较弱。③降水对净辐射的分配起重要作用,降水增加,潜热增加。④表层土壤水分受降水和LAI调控,与潜热有相反的变化趋势。

The contributions of leaf area index and precipitation to surface energy balance in the process of land cover change

Leaf area index (LAI), which has interaction with a variety of elements such as precipitation in the process of land use and cover change, is an important influencing factor of the surface energy balance. But its contribution to the surface energy balance in the process of land use and cover change is unclear. This article emphatically isolated the impact of LAI on surface energy balance, in order to recognize the relative role of land cover and LAI in surface energy balance. The research objects include: three kinds of land cover, i.e. farmland, forest and grassland in northeast China, the corresponding LAI monthly data (annual average 1.21, 1.64 and 0.73 (m²m^-2), respectively), and three arbitrary kinds of precipitation amount (double, normal and half) in 2003. Firstly the Simple Biosphere model 2 had been validated against net radiation, sensible heat, latent heat, and temperature at the study sites, and showed well performance on yearly change trends. Then the effects on surface energy balance of different combinations of land cover and LAI data under different rain amount conditions were studied using the model. We found that, (1) land cover change had the biggest impacts on net radiation, with annual average (Wm^-2) about 14.5 compared with less than 1.57 and 0.49 for LAI and precipitation influence; (2) LAI mainly altered the partitioning of net radiation into latent and sensible heat flux, i.e. bigger LAI obviously increased (decreased) the ratio of latent (sensible) heat flux in net radiation at farmland and grassland, and LAI variation had less influence on latent and sensible heat flux at forest; (3) precipitation played an important role in net radiation partitioning, that is latent heat flux increased with more precipitation, but half times precipitation amount had more sharp effect than double times precipitation amount; (4) surface soil moisture was regulated by precipitation and LAI, and had an opposite variation tendency against latent heat. We also showed that the relationships between LAI and surface energy balance components at monthly scale were coincident with that at yearly scale. Our results proved the importance of LAI in surface energy partitioning into latent and sensible heat flux in the process of land use and cover change.