National Aeronautics and Space Administration Jet Propulsion Laboratory
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology SMAP Improves Global Evapotranspiration Adam J. Purdy Science: The Soil Moisture Active Passive (SMAP) mission was launched as a Tier 1 Decadal Survey 2007 mission. The objectives of SMAP are to: 1) “estimate global water and energy fluxes at the land surface” and 2) “understand processes that link the terrestrial water, energy and carbon cycles. ” Here, we achieve these objectives by using SMAP soil moisture to generate global maps of evapotranspiration (ET), thereby linking the water, energy, and carbon cycles through SMAP soil moisture. Results: First, we assessed the new ET data at multiple validation sites around the world. The largest improvements to ET with SMAP occurred in dry regions. Next, we quantified the dominant components of ET globally and in doing so advanced understanding of key processes that links the water and energy cycles (Figure 1). Significance: Recent evidence suggests that the hydrological cycle is accelerating, with ET playing a central role. As the land surface dries, quantifying where and to what degree reductions in water availability are related to ET and soil moisture becomes increasingly important. Because of the new and critical information from SMAP in ET, we can better identify thresholds and quantify ecosystem impacts related to changes in water distribution. Figure 1: ET components as a percentage of total ET. Red indicates more soil evaporation, blue indicates more canopy transpiration, yellow indicates more interception evaporation. Purdy, A. J. , Fisher, J. B. , Goulden, M. L. , Colliander, A. , Halverson, G. , Tu, K. , Famiglietti, J. S. , 2018. SMAP soil moisture improves global evapotranspiration. Remote Sensing of Environment. AJP was supported by the NASA Earth and Space Science Fellowship 17 -EARTH 17 R-0062 and SUSMAP (Entin). PI: JBF supported by SUSMAP.
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Contact: Adam J. Purdy, M/S 233 -300, Jet Propulsion Laboratory, Pasadena, CA 91109 adam. j. purdy@jpl. nasa. gov Citation: Purdy, A. J. , Fisher, J. B. , Goulden, M. L. , Colliander, A. , Halverson, G. , Tu, K. , Famiglietti, J. S. , 2018. SMAP soil moisture improves global evapotranspiration. Remote Sensing of Environment. Data Sources: SMAP: https: //n 5 eil 01 u. ecs. nsidc. org, MODIS: https: //e 4 ftl 01. cr. usgs. gov/, MERRA: https: //goldsmr 4. gesdisc. eosdis. nasa. gov: 443 Scientific significance, societal relevance, and relationships to future missions: Based on the results in this study we conclude that modifications to the PT-JPL ET algorithm to include soil moisture produce more realistic ET estimates globally. Incorporating soil moisture from SMAP resulted in lower estimates of evaporation and transpiration in water-limited regions. These lower ET estimates have implications for feedbacks between the water cycle and the carbon cycle. This new dataset provides the opportunity to identify vegetation vulnerable to drought and water limiting conditions and compare with the carbon cycle ecosystem response as seen by OCO-2. Lastly, the results from this study directly achieves 2 of the key science objectives of the SMAP mission by advancing the “understand[ing] processes that link the terrestrial water, energy and carbon cycles” and “estimat[ing] global water and energy fluxes at the land surface. ”
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