GC029-08
Comparing and validating measures of water-use efficiency from NASA's ECOSTRESS mission

Tuesday, 8 December 2020: 05:58
Virtual
Gregory R. Goldsmith, Chapman University, Orange, CA, United States, Joshua Fisher, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, Imma Oliveras, University of Oxford, Environmental Change Institute, Oxford, United Kingdom, Yadvinder Malhi, University of Oxford, School of Geography and the Environment, Oxford, United Kingdom and Chris Doughty, Northern Arizona University, Flagstaff, AZ, United States
Recorded Presentation
Abstract:
NASA’s new remote sensing mission, the ECOsystem Spaceborn Thermal Radiometer Experiment on Space Station (ECOSTRESS), provides estimates of land surface temperature, evapotranspiration, and plant water-use efficiency (WUE; photosynthetic carbon assimilation per unit water loss) at 70 m resolution every few days. The unprecedented spatial and temporal resolution of the estimates has the potential to transform our understanding of how water, carbon, and energy flow through the terrestrial biosphere. However, to realize the full potential of the mission, it is critical that we test, validate and refine the methods used for making these estimates.

To test and validate ECOSTRESS, we focus on generating and comparing standardized calculations of WUE from ECOSTRESS that are scaled as a function of the vapor pressure deficit. These estimates can then be compared to ground-based leaf-level gas exchange, leaf tissue carbon and oxygen isotopes, and flux tower data. We use both a case study approach drawn from a savannah to forest transition zone in the Brazilian Amazon (a region of high WUE uncertainty), as well as a global comparison based on an existing data set.

ECOSTRESS observes strong diurnal patterns of evapotranspiration that increase in magnitude across the savannah to forest transition zone, which is consistent with expectations. However, no clear pattern of WUE emerges in either ECOSTRESS or ground-based observations across that same transition, likely due to the lack of clear differences in photosynthetic carbon assimilation. At the global scale, we find that current ECOSTRESS estimates of WUE are affected by the inclusion of soil evaporation in the calculation. Patterns observed among different measures of WUE, as observed across plant functional types, suggest strong fidelity, but are likely to be particularly sensitive to misestimates of photosynthesis (i.e., gross primary productivity). We provided recommendations to the ECOSTRESS mission on improvements to the WUE retrieval based on refined calculations and using transpiration only. The mission has adopted these recommendations and they are included in the next data release of ECOSTRESS.

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