Influences of Vegetation Phenological Shifts on Water and Energy Cycle

Remote sensed vegetation indices and field measurements have demonstrated that climate change has influenced vegetation phenology. The phenological changes are expressed in shifts in the timing of spring vegetation activity and the length of the active growing season. According to NDVI data from NOAA and GIMMS, the length of the active growing season north of 45°N has extended by 12 days due to 8 days advancement in spring and 4 days prolongation in autumn between July 1981 and June 1991. The same NDVI dataset from July 1981 to December 1999 has shown the growing season increased by 18 days in Eurasia and 12 days in North America. Phenology regulates vegetation interactions with climate by influencing the energy, water and carbon cycles. Here, we use observations and the Community Land Model 4.5 (CLM4.5) in offline mode and coupled with CESM to evaluate influences of shifts in phenology on energy and water budget and partitioning and on interactions with the atmosphere. Satellite retrieved leaf area index (LAI) is used to prescribe shifts in vegetation phenology in CLM4.5. We find that phenological advancement of 12 days over the past few decades can result in monthly mean changes of (-5-7 Wm-2) in latent heat and (-5-9Wm-2) in sensible heat balance over wide regions. We will discuss (1) the capability of current climate models to predict the impacts of phenological shifts on climate change, (2) seasonal to annual changes in energy and water cycles in response to phenological shifts, (3) the spatial heterogeneity in phenological-induced energy and water partitioning in different plant functional types across regions and continents, and (4) phenology and plant-climate interactions in changing climate.