植被覆盖异常变化影响陆面状况的数值模拟

利用NCAR最新的公用陆面模式CLM3．0，通过数值模拟初步研究了植被叶面积指数（LAI，leafareaindex）异常变化对陆面状况的可能影响，结果表明，植被LAI的异常变化能够引起地表能量平衡、地表水循环等陆面状况的异常。（1）植被LAI的异常变化主要影响太阳辐射在植被与地表之间的分配，以及地表的感热、潜热通量。植被LAI增大，能够引起植被吸收的太阳辐射增加，而到达土壤表面的太阳辐射减小，并导致植被的蒸发、蒸腾潜热通量增加，造成地表的蒸发潜热和感热通量不同程度的减小。（2）植被LAI增大时，植被对降水的拦截和植被叶面的蒸发增大，植被的蒸腾作用也明显增强；植被LAI增加会使得热带地区各个季节的土壤表面蒸发、地表径流减小，而土壤湿度有所增加；LAI增加造成中高纬度地区土壤蒸发的减少主要出现在夏季；LAI增加还能够引起中高纬地区冬、春积雪深度不同程度的增加，造成春末、夏初地表径流的增加。（3）植被LAI增加能够使得叶面和土壤温度有所下降，但植被LAI的变化对叶面、土壤温度的影响相对较小。

Modeling of Impacts of Vegetation Coverage Change on Land Surface Conditions

Impacts of vegetation coverage changes on land surface conditions are investigated through numerical simulation by using the NCAR Community Land Model(CLM3.0).Results show that the evident anomalies in land surface conditions,such as energy balance and hydrological cycle,are induced by anomalous changes in vegetation leaf area index(LAI).(1)The anomalous change in LAI alters the partitioning of the solar radiation reaching at ground surface between vegetation and soil surface,as well as the sensible and latent heat fluxes of ground surface.Larger LAI increases the solar radiation absorbed by the vegetation,but decreases that arriving at the soil surface.Meanwhile,it also induces increase in the latent heat flux related to the vegetation evaporation and transpiration,together with decrease in ground surface latent heat and sensible heat fluxes.(2) The increase of LAI leads to a larger precipitation interception,leaf evaporation and transpiration.In the tropics,larger LAI leads to smaller soil evaporation and land surface runoff,but larger soil moisture in all seasons.However,in the middle-high latitudes of Northern Hemisphere increase in LAI reduces the soil evaporation mainly in summer,and also results in deeper snow cover in winter,thus causing an evident increase in land surface runoff in late spring and early summer.(3)Larger LAI tends to reduce both leaf temperature and ground temperature,but only by relatively small values.Such a conclusion will provide some clues for further investigation on the climatic feedbacks of the vegetation coverage change.