A water budget approach shows complex seasonal cycle and long-term changes in tropical forest function.
The NGEE-Tropics research team combined satellite measurements of rainfall and gravity anomalies with Amazon River flow data to derive a seasonally-resolved estimate of evapotranspiration for the entire Amazon basin. Next the team analyzed the seasonal cycles and long-term variation of this measurement and compared it to process-based land surface model predictions.
The study’s results show a more complex and different seasonal cycle than current land surface models predict. The study suggests a long-term decline in evapotranspiration from the forest, due to ecosystem functional change at the scale of the entire basin.
Evapotranspiration, which comprises the sum of all moisture fluxes from an ecosystem directly to the atmosphere, is a crucial quantity at the center of the terrestrial energy, water, and carbon cycles. Because measurements of evapotranspiration are typically made at local scales, and are sparse over remote locations such as the Amazon, the larger-scale fluxes are not well known. This study combined observations of rainfall, river discharge, and time-varying gravity anomalies to construct a water budget for the Amazon basin, which allows the NGEE-Tropics researchers to solve for evapotranspiration as the missing term in the budget. This water budget-based measurement shows a complex seasonal cycle, with a deeper minimum during the wet season than is estimated by other upscaling estimates or by process-based models, and also shows that models tend to increase their seasonal evapotranspiration fluxes later in the dry season than is observed. Furthermore, a long-term analysis of evapotranspiration suggests a decline in the rate over the period of observation, which could be evidence of a large-scale change in ecosystem function.
Contacts (BER PM)
Daniel Stover, Dorothy Koch, Renu Joseph
Lawrence Berkeley National Laboratory
ALSS was supported by National Science Foundation grants AGS-1321745 and AGS-1553715. CDK received support from the Regional and Global Climate Modeling program through the BGC-Feedbacks SFA and the Terrestrial Ecosystem Sciences and Earth System Modeling programs through the Next Generation Ecosystem Experiments-Tropics (NGEE-Tropics) project of the Biological and Environmental Research (BER) Program in the U. S. Dept. of Energy Office of Science.
Swann, A. L. S., and Koven , C. D. A direct estimate of the seasonal cycle of evapotranspiration over the Amazon. Journal of Hydrometeorology (2017). [doi:10.1175/JHM-D-17-0004.1] (Reference link)
SC-23.1 Climate and Environmental Sciences Division, BER
New Approach for Studying How Microbes Influence Their Environment
A diverse group of scientists suggests a common framework and targeting of known microbial processes [more...]
Nutrient-Hungry Peatland Microbes Reduce Carbon Loss Under Warmer Conditions
Enzyme production in peatlands reduces carbon lost to respiration under future high temperatures. [more...]
Amazon Forest Response to CO2 Fertilization Dependent on Plant Phosphorus Acquisition
AmazonFACE Model Intercomparison. The Science Plant growth is dependent on the availabi [more...]
A Slippery Slope: Soil Carbon Destabilization
Carbon gain or loss depends on the balance between competing biological, chemical, and physical reac [more...]
Field Evaluation of Gas Analyzers for Measuring Ecosystem Fluxes
How gas analyzer type and correction method impact measured fluxes. The Science A side- [more...]
List all highlights (possible long download time)