Mapping water status within a Mediterranean vineyard watershed: implication for validation, modelling and digital soil mapping
Year: 2010
Type: conference-paper
Abstract: As an influence factor for topsoil and root zone moisture, daily Evapo-Transpiration (ET) containsvaluable information for i) characterizing the hydrological cycle in relation to land surface boundaryconditions, ii) forecasting vine production in relation to water stress at different growth stages, andiii) digitally mapping soil properties in relation to subsurface water transfers. We address here themapping of daily ET at the regional extent over a vineyard watershed, by focusing on i) the validationexercise at the regional extent, ii) the remote sensing approaches to be considered over a rowstructured complex landscape, and iii) the informative value of daily ET for the digital mapping of soilproperties. The study area is the 70 sq-km size Peyne watershed, located in southern FranceLanguedoc-Roussillon region. The experiment spread over two vine growth cycles in 2007 and 2008.The validation exercise is conducted at seven sites disseminated within the watershed, to capturespatial and temporal variations. In-situ daily ET is estimated from the HYDRUS-1D model thatsimulates water transfers within the vadoze zone. This allows to minimize experimental efforts, sincethe required observations can be collected automatically (meteorological forcing) or manually with athree week frequency (soil moisture profile and watertable level). HYDRUS-1D simulations arecontrolled through i) the residual error on model calibration against soil moisture profiles within allsites, and ii) the differences in daily ET against Eddy Covariance estimates within two contrasted sites.The results, about 10% in relative for temporal changes in soil water storage, and between 0.4 and0.6 mm/day for daily ET, emphasize the relevance HYDRUS-1D simulations as ground truthing.Given the complex parameterization to be implemented if considering a two source model that splitssoil and vegetation, daily ET is derived from ASTER observations by using surface temperaturedifferencing that minimizes data and parameterization errors. We select i) S-SEBI that relies ontemperature differences and albedo only, thus avoiding delicate computations, and ii) WDI that refinesthe temperature differencing through the use of physical formulations rather than contextual estimates.Validation over the seven sites for 20 ASTER scenes indicates performances slightly better for S-SEBI(0.8 mm/day) than WDI (1.1 mm/day), whereas model intercomparison at the watershed extentshowed differences about 1 mm/day. Sensitivity studies indicates S-SEBI is sensitive to the study areaextent and WDI is sensitive to wind speed, with similar magnitudes (40% in relative). In both cases,sensitivity originates in the derivation of evaporative extremes for temperature differencing.Regardless of differencing approach, the obtained maps of daily ET depict similar patterns throughoutthe experiment. We therefore assess to use of daily ET and Vegetation Indexes (VIs) as proxies of vineaccess to groundwater, where the latter is characterized by soil depth and watertable level, both highlyvariable within the Peyne watershed. ET and VI proxies are considered through temporal changesinduced by water stress and vegetation growth. Additional proxies based on topography are alsoconsidered, to account for pedogenesis. Data mining with a classification and regression tree approachindicates two overlapping populations for daily ET, which relate to indirect or direct vine access togroundwater. VIs and ET provided a reasonable fit for soil depth (r² = 0.53) but inclusion of terrainattributes improves the fit (r² = 0.90). Directly modelling the watertable level is unsuccessful becauseof cross interactions. When watertable is accessible, it is not possible to identify any combinationbetween i) shallow watertable with a shallow or deep soil or ii) deep soil and deep watertable.
Source: HAL
Language: English
Subfield: Environmental Engineering
Field: Environmental Science
Domain: Physical Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W3041941334