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Rootzone Soil Moisture Dynamics Using Terrestrial Water-Energy Coupling
  • Vinit Sehgal,
  • Binayak Mohanty,
  • Rolf Reichle
Vinit Sehgal
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Binayak Mohanty

Corresponding Author:bmohanty@tamu.edu

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Rolf Reichle
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Abstract

A lack of high-density rootzone soil moisture (θRZ) observations limits the estimation of continental-scale, space-time contiguous θRZ dynamics. We derive a proxy of daily θRZ dynamics ― active rootzone degree of saturation (SRZ ) ― by recursive low-pass (LP) filtering of surface soil moisture (θS) within a terrestrial water-energy coupling (WEC) framework. We estimate the LP filter parameters and WEC thresholds for the piecewise-linear coupling between SRZ and evaporative fraction (EF) at remote sensing and field scale over Contiguous U.S. We use θS from Soil Moisture Active-Passive (SMAP) satellite and 218 in-situ stations, with EF from Moderate Resolution Imaging Spectroradiometer. The estimated SRZ  shows high validation skill against SMAP Level-4 estimates and in-situ θRZ, at the corresponding scale. The instantaneous hydrologic state of SRZ vis-à-vis the WEC thresholds is proposed as a rootzone soil moisture stress index (SMSRZ) for near-real-time operational agricultural drought monitoring― demonstrating high agreement with established drought metrics.