Tropical Terrestrial Tipping Point

Ian Baker, Colorado State University, baker@atmos.colostate.edu (Presenter)
Katherine Haynes, Colorado State University, kdhaynes@atmos.colostate.edu
Scott Denning, Colorado State University, denning@atmos.colostate.edu
Don Dazlich, Colorado State University, dazlich@atmos.colostate.edu
David Randall, Colorado State University, randall@atmos.colostate.edu
Anna Harper, University of Exeter, a.harper@exeter.ac.uk

Tropical Forests contain massive carbon stores whose viability under climate change is uncertain, and surface flux response to seasonal and interannual drought is poorly understood under even present climatic conditions. Dire predictions of evergreen tropical forest conversion to savanna or grassland have been scaled back recently, yet the occurrence of two ‘once in a lifetime’ droughts within the last 10 years underscores the need to quantify tropical forest hydrodynamics across vegetation and moisture gradients.

We are combining ongoing surface biophysical investigations with innovative modeling frameworks to evaluate and predict surface behavior and the coupled land-atmosphere system under present and future climate. We are presently evaluating components of the full system in anticipation of simulations using the full model framework. These components include 1) surface ecophysiological behavior across vegetation and moisture gradients, and 2) the representation of the vegetated land surface within superparameterized (SP-) Atmospheric General Circulation Models such as the Community Earth System Model (SP-CESM). We evaluate surface flux and biomass against eddy covariance flux towers as well as a large suite of satellite observations (LAI/fPAR, aboveground biomass, Solar Induced Fluorescence-SIF). We have also developed the Drought Stress Resilience Index (DRSI) as a means to further quantify and constrain spatial response to interannual drought. We are presently evaluating coupled land-atmosphere behavior across multiple AGCM configurations to determine to which surface-atmosphere exchange is determined by model structure.

The previous generation of land models was oversensitive to even seasonal drought in evergreen tropical forests. Recent modifications have made our models somewhat over-resilient, and goal is that DRSI will impose a more realistic response to interannual precipitation variability while maintaining a realistic seasonal simulation of carbon, energy and moisture flux. Coupled land-atmosphere simulations show similarity in general behavior such as precipitation while simultaneously expressing a wide diversity of surface flux that will likely lead to divergence between global simulations across long time scales.

Presentation Type:  Poster

Session:  General Contributions   (Tue 4:35 PM)

Associated Project(s): 

• Denning, Scott: The Tropical Terrestrial Tipping Point: Drought Stress and Resilience in Moist Tropical Forests ...details

Poster Location ID: 137