The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat

Abstract

Abstract. Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. A way to quantify the spatial distribution of evapotranspiration and water stress from remote-sensing data is to exploit the available surface temperature as a signature of the surface energy balance. Remotely sensed energy balance models enable to estimate stress levels and, in turn, the water status of continental surfaces. Dual-source models are particularly useful since they allow deriving a rough estimate of the water stress of the vegetation instead of that of a soil–vegetation composite. They either assume that the soil and the vegetation interact almost independently with the atmosphere (patch approach corresponding to a arallel resistance scheme) or are tightly coupled (layer approach corresponding to a series resistance scheme). The water status of both sources is solved simultaneously from a single surface temperature observation based on a realistic underlying assumption which states that, in most cases, the vegetation is unstressed, and that if the vegetation is stressed, evaporation is negligible. In the latter case, if the vegetation stress is not properly accounted for, the resulting evaporation will decrease to unrealistic levels (negative fluxes) in order to maintain the same total surface temperature. This work assesses the retrieval performances of total and component evapotranspiration as well as surface and plant water stress levels by (1) proposing a new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) in two versions (parallel and series resistance networks) based on the TSEB (Norman et al., 1995) model rationale as well as state of the art formulations of turbulent and radiative exchange, (2) challenging the limits of the underlying hypothesis for those two versions through a synthetic retrieval test and (3) testing the water stress retrievals (vegetation water stress and moisture-limited soil evaporation) against in-situ data over contrasted test sites (irrigated and rainfed wheat). We demonstrated with those two datasets that the series model is more robust to component stress retrieval for this cover type, that its performance increases by using bounding relationships based on potential conditions (root mean square error lowered by up to 11 W m-2 from values of the order of 50–80 W m-2), and that soil evaporation retrieval is globally consistent with an independent estimate from observed soil moisture evolution.

Evapotranspiration partition using the multiple energy balance version of the ISBA-A-g<sub>s</sub> land surface model over two irrigated crops in a semi-arid Mediterranean region (Marrakech, Morocco)

“…These good performances are in agreement with results reported in the literature. Indeed, several studies showed that the estimation of R n by SVAT models is good on several type of canopy , Boulet et al, 2015and 2009a. The most important differences are encountered on the Agdal site and can be explained by the slight overestimation (not shown) of the infrared radiation (LW up ) by ISBA-2P for both seasons (Bias=13.7 and 12.7 420 W/m 2 for the 2003 and 2004 seasons, respectively).…”

“…The representation of the intensity of this coupling, and ultimately the performance of the models to reproduce the ET and its partition, is directly related to the structure adopted in the model (single-or dual-source). In particular, it has been shown that a more realistic representation of the energy balance and a better representation of the respective contributions of E and T r to ET (Shuttleworth and Wallace, 1985;Norman et al, 1995;Béziat et al, 2013;Boulet et al, 2015) could be obtained by solving several separate 95 energy balances for each of the sources. In this context, two types of dual-source models were developed (Lhomme et al, 2012).…”

“…By contrast, for the patch representation, soil and vegetation turbulent processes are independent and soil receives the full incoming radiation not screened by the vegetation (Norman et al, 1995;Kustas and Norman, 1997;Boulet et al, 2015). The choice between the patch and the layer approach is related to the scale of the surface heterogeneity (Lhomme and Chehbouni, 1994;Boulet et al, 1999;Lhomme et al, 1999;Blyth and Harding, 1995;Lhomme et al, 2012).…”

Remote Sensing Energy Balance Model for the Assessment of Crop Evapotranspiration and Water Status in an Almond Rootstock Collection

“…In recent years, improvements in computational performance, open-source programming languages, lower data requirements, and the simplification of different complex approaches used to estimate actual crop evapotranspiration (ET a ) through RS have contributed, at least in part, to reducing the existing gap between RS physical modeling methods and agricultural applications. Among the different methods, the surface energy balance (SEB) models are probably the most complex to run, but at the same time provide high accuracy and robustness in estimating ET a in different environments ( Norman et al, 1995 ; Bastiaanssen et al, 1998 ; Mecikalski et al, 1999 ; Allen et al, 2007 ; Boulet et al, 2015 ). These models have mostly been used for assessing the spatial and temporal variability of ET a at regional and field scale using satellite imagery ( Semmens et al, 2016 ; He et al, 2017 ; Knipper et al, 2019 ), although some of them have also been used with very high-resolution aircraft imagery ( Hoffman et al, 2016 ; Xia et al, 2016 ; Nieto et al, 2019 ).…”