Abstract ID: 486

The Relationship between surface biophysics in the Amazon rainforest and regional climate

Approximately half of the Amazon’s evergreen forests are subjected to dry seasons of at least three months, yet the forest seems to thrive during the dry, sunny months. Dry season evapotranspiration is often greater than during the wet season. Observations show that trees in the Amazon are able to access deep soil moisture by using tap roots with depths of 11 meters or more. However, ecosystem models often inaccurately simulate seasonal cycles of forest evapotranspiration, which can trigger severe feedbacks to the climate in coupled models. We investigate the climatic impacts of the ability of deep roots to access adequate soil moisture by coupling the Simple Biosphere (SiB3) model to Colorado State University’s general circulation model, BUGS5. We compare two versions of SiB3 in the GCM. The first has strong vegetative stress due to soil moisture limitations. The second experiences less stress and has more realistic representations of surface biophysics. In the model, basin-wide reductions in soil moisture stress result in increased evapotranspiration, precipitation, and moisture recycling in the Amazon basin. In the savannah region of southeastern Brazil, the unstressed version of SiB3 produces decreased precipitation and weaker moisture flux, which is more in-line with observations. The improved simulation of precipitation and evaporation also produces a more realistic Bolivian high and Nordeste low. In the unstressed version of SiB3, the circulation around the Bolivian high is stronger, the trough around the Nordeste low is better defined, and the low is located closer to observations compared to the stressed version of SiB3. These changes highlight the importance of subsurface biophysics for the Amazonian climate. We also investigate feedbacks to the global climate. In particular, preliminary results suggest a large increase in evaporation from Northern Hemisphere continents during the boreal summer.

Session:  Feedbacks to Climate - Land cover, surface hydrology, and atmospheric feedbacks. (B)

Presentation Type:  Oral