Joel A. Biederman - Weekly Coloquium - 01.26.2017

How water and plants interact to regulate water supply, water quality, and carbon sequestration in the water-limited Southwest

Joel A. Biederman

Research Hydrologist
Southwest Watershed Research Center
USDA Agricultural Research Service
Tucson, Arizona

Compound changes in climate and land cover challenge understanding of watershed services including water supply, water quality, and atmospheric carbon sequestration.  Vegetation strongly controls the hydrologic and carbon cycles, which feed back to regulate vegetation structure and function.  Here I present research at this intersection of ecosystems and the hydrologic and carbon cycles, in three parts:

1.   Forest die-off across watersheds of western North America has raised concerns for altered water supply and quality.  Using nested observations from plot to basin scales, we quantify how die-off impacts land-atmosphere hydrologic partitioning and lateral hydrologic and biogeochemical fluxes.  We find water supply and quality to be resilient due to counteracting responses of individual processes including transpiration , evaporation, and snow sublimation. 

2.    After a century of fire suppression, land managers are reducing forest fuels density, with unknown consequences for water balance, particularly snowpack.  We have developed a forest hydrologic model using LiDAR datasets to represent spatially explicit interactions of weather, vegetation, and terrain at individual tree resolution (~1 m).  We collaborate with Arizona land and water mangers to train the model for forests undergoing thinning treatments and to develop operational tools for water supply forecasting. 

3.    Global-scale studies suggest that drylands dominate an increasing trend in the magnitude and interannual variability of the land CO2 sink, but measurements are lacking.  Across 25 Southwest eddy covariance sites, we find a wide range of carbon sink/source function varying from -350 to +330 gCm-2, contrasting with the more constant sink typical of mesic ecosystems.   Interannual variability was larger than for mesic regions, and half the sites switched between sinks/sources in wet/dry years.   MODIS-based models matched the cross-site spatial pattern in mean annual GEP but consistently underestimated mean annual ET by ~50%.   Importantly, the models captured only 20-30 % of interannual variation, suggesting the contribution of this dryland region to variability of global CO2 exchange may be 3 – 5 times larger than current estimates.


 Dr. Joel Biederman Biosketch

Joel Biederman is a research hydrologist at the Southwest Watershed Research Center in Tucson, Arizona.  He works to understand the impacts of climate and land use changes on watershed services and to develop new tools for sustainable watershed management.    Joel holds bachelor’s and master’s degrees in civil and environmental engineering from Montana State University.  He completed his Ph.D. in Hydrology and Water Resources at the University of Arizona in 2013, where he earned the Centennial Award for Doctoral Achievement.  Joel has held prior positions on the science faculty at Suffield Academy and as a research engineer at the NSF Center for Biofilm Engineering.  Joel’s research has been recently featured in an EOS Research Spotlight and a Fluxnet Feature. 

Joel Biederman
Research Hydrologist
Southwest Watershed Research Center
USDA - Agricultural Research Service