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Article

Estimating Soil Evaporation Using Drying Rates Determined from Satellite-Based Soil Moisture Records

1
Geological Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
2
Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado Boulder, Boulder, CO 80309, USA
3
Department of Civil, Environmental, and Architectural Engineering, University of Colorado Boulder, Boulder, CO 80309, USA
*
Author to whom correspondence should be addressed.
Remote Sens. 2018, 10(12), 1945; https://doi.org/10.3390/rs10121945
Received: 18 August 2018 / Revised: 16 November 2018 / Accepted: 27 November 2018 / Published: 4 December 2018
(This article belongs to the Special Issue Soil Moisture Remote Sensing Across Scales)
We describe an approach (ESMAP; Evaporation–Soil Moisture Active Passive) to estimate direct evaporation from soil, Esoil, by combining remotely-sensed soil drying rates with model calculations of the vertical fluxes in and out of the surface soil layer. Improved knowledge of Esoil can serve as a constraint in how total evapotranspiration is partitioned. The soil drying rates used here are based on SMAP data, but the method could be applied to data from other sensors. We present results corresponding to ten SMAP pixels in North America to evaluate the method. The ESMAP method was applied to intervals between successive SMAP overpasses with limited precipitation (<2 mm) to avoid uncertainty associated with precipitation, infiltration, and runoff. We used the Hydrus 1-D model to calculate the flux of water across the bottom boundary of the 0 to 50 mm soil layer sensed by SMAP, qbot. During dry intervals, qbot typically transfers water upwards into the surface soil layer from below, usually <0.5 mm day−1. Based on a standard formulation, transpiration from the surface soil layer, ET_s, is usually < 0.1 mm day−1, and, thus, generally not an important flux. Soil drying rates (converted to equivalent water thickness) are typically between 0 and 1 mm day−1. Evaporation is almost always greater than soil drying rates because qbot is typically a source of water to the surface soil and ET_s is negligible. Evaporation is typically between 0 and 1.5 mm day−1, with the highest values following rainfall. Soil evaporation summed over SMAP overpass intervals with precipitation <2 mm (60% of days) accounts for 15% of total precipitation. If evaporation rates are similar during overpasses with substantial precipitation, then the total evaporation flux would account for ~25% of precipitation. ESMAP could be used over spatially continuous domains to provide constraints on Esoil, but model-based Esoil would be required during intervals with substantial precipitation. View Full-Text
Keywords: remote sensing; SMAP; evaporation; soil moisture remote sensing; SMAP; evaporation; soil moisture
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MDPI and ACS Style

Small, E.E.; Badger, A.M.; Abolafia-Rosenzweig, R.; Livneh, B. Estimating Soil Evaporation Using Drying Rates Determined from Satellite-Based Soil Moisture Records. Remote Sens. 2018, 10, 1945. https://doi.org/10.3390/rs10121945

AMA Style

Small EE, Badger AM, Abolafia-Rosenzweig R, Livneh B. Estimating Soil Evaporation Using Drying Rates Determined from Satellite-Based Soil Moisture Records. Remote Sensing. 2018; 10(12):1945. https://doi.org/10.3390/rs10121945

Chicago/Turabian Style

Small, Eric E., Andrew M. Badger, Ronnie Abolafia-Rosenzweig, and Ben Livneh. 2018. "Estimating Soil Evaporation Using Drying Rates Determined from Satellite-Based Soil Moisture Records" Remote Sensing 10, no. 12: 1945. https://doi.org/10.3390/rs10121945

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