Impact of regional characteristics on the estimation of root-zone soil moisture from the evaporative index or evaporative fraction

Shukran A. Sahaar and Jeffrey D. Niemann

Agricultural Water Management, 2020, vol. 238, issue C

Abstract: Accurate knowledge of root-zone soil moisture is of vital significance to many applications in agriculture, such as crop yield estimation, precision irrigation, salinity and groundwater management. Remote-sensing methods based on optical and thermal satellite imagery have been proposed to estimate fine-resolution (30 m grid cells) maps of root-zone soil moisture θ¯ or degree of saturation s¯ over large regions. These methods usually calculate the evaporative fraction ΛSEB as the ratio of the latent heat flux to the difference of the net radiation and ground heat flux. Then, they estimate θ¯ or s¯ from an empirical relationship with ΛSEB. A similar approach estimates θ¯ or s¯ using the evaporative index ΛPET, which is the ratio of the actual to potential evapotranspiration. However, previous research has shown that a single relationship between either θ¯ or s¯ and ΛSEB does not apply to all regions. The objective of this study is to evaluate the impact of regional soil, vegetation, and climatic conditions on the form and strength of the ΛSEB−θ¯, ΛPET−θ¯, ΛSEB−s¯, and ΛPET−s¯ relationships. To accomplish this goal, Extended Fourier Amplitude Sensitivity Test (eFAST) is applied to a physically-based model (HYDRUS 1-D) that simulates both evapotranspiration and soil moisture dynamics. The sensitivity results show that, within a given climatic region, soil characteristics such as the percent clay and percent silt are most important in determining the shape of the relationships, while vegetation characteristics such as leaf area index and maximum rooting depth have the greatest effect on the strength of these relationships. The total annual precipitation, which helps determine the climatic region, also has a strong effect on both the form and strength of the relationships. The parameters that define the ΛSEB−θ¯ and ΛPET−θ¯ relationships are also estimated using the regional characteristics. Estimating the parameters in this way allows the methods to be adapted to local conditions and has the potential to improve the θ¯ and s¯ estimates.

Keywords: Soil moisture; Root zone; Evaporative fraction; Evaporative index; HYDRUS 1-D; eFAST (search for similar items in EconPapers)
Date: 2020
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Citations: View citations in EconPapers (2)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:agiwat:v:238:y:2020:i:c:s0378377419318281

DOI: 10.1016/j.agwat.2020.106225

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