报告题目：A better way of representing stem area index in two-big-leaf models

　　报 告 人：Dr. Ming Chen

　　单 位：Department of Forest Resources, University of Minnesota

　　报告时间：2017年6月21日上午10:00

　　地 点：科研楼303会议室

　　报告摘要

　　In order to better estimate the carbon budget of the globe, accurately simulating gross primary productivity (GPP) in terrestrial ecosystem models is critical. When upscaling leaf level photosynthesis to the canopy, climate models uses different big-leaf schemes. Some models use a “two-big-leaf” scheme that partitions canopies into direct and diffusively illuminated fractions to reduce high bias of GPP simulated by one-big-leaf models. Some two-big-leaf models, such as ACME (identical in this respect to CLM 4.5) add leaf area index (LAI) and stem area index (SAI) together when calculating canopy radiation transfer. This treatment, however, will result in higher fraction of sunlit leaves. It will also lead to an artificial overestimation of canopy nitrogen content. Here we introduce a new algorithm of simulating SAI in a two-big-leaf model. The new algorism reduced the sunlit leave fraction of the canopy and conserved the nitrogen content from leaf to canopy level. The lower fraction of sunlit leaves reduced global GPP especially in tropical area. Model calculated global GPP was reduced by 4.19 PgC year-1.