Abstract
This study aims at illustrating a methodology for predicting monthly scale actual evapotranspiration losses only based on meteorological data, which mimics the evapotranspiration intra-annual dynamic. For this purpose, micrometeorological data at the Rollesbroich and Bondone mountain sites, which are energy-limited systems, and the Sister site, a water-limited system, have been analyzed. Based on an observed intra-annual transition between dry and wet states governed by a threshold value of net radiation at each site, an approach that couples meteorological data-based potential evapotranspiration and actual evapotranspiration relationships has been proposed and validated against eddy covariance measurements, and further compared to two well-known actual evapotranspiration prediction models, namely the advection-aridity and the antecedent precipitation index models. The threshold approach improves the intra-annual actual evapotranspiration variability prediction, particularly during the wet state periods, and especially concerning the Sister site, where errors are almost four times smaller compared to the basic models. To further improve the prediction within the dry state periods, a calibration of the Priestley-Taylor advection coefficient was necessary. This led to an error reduction of about 80% in the case of the Sister site, of about 30% in the case of Rollesbroich, and close to 60% in the case of Bondone Mountain. For cases with a lack of measured data of net radiation and soil heat fluxes, which are essential for the implementation of the models, an application derived from empirical relationships is discussed. In addition, the study assessed whether this variation from meteorological data worsened the prediction performances of the models.
Highlights
Evapotranspiration (ET) is a major component in the water balance of hydrological systems [1,2].It is a critical parameter in hydrological applications and uncertainties in its assessment propagate through the hydrological soil–water balance [3]
Distinctions can be made between potential evapotranspiration (PET) and actual evapotranspiration (AET)
The threshold approach has significantly improved the monthly scale prediction of evaporative demands during the wet state periods, in particular for the Mediterranean forested Sister site water-limited system
Summary
Evapotranspiration (ET) is a major component in the water balance of hydrological systems [1,2]. It is a critical parameter in hydrological applications and uncertainties in its assessment propagate through the hydrological soil–water balance [3]. Potential evapotranspiration measures the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration when no limitation or control on water supply exists. Actual evapotranspiration is the quantity of water removed by evaporation and transpiration from a surface if the total amount of water is limited. Long-term ET measurements are complex and costly to obtain and, even if some observational data exist, methods to assess ET fluxes such as the eddy covariance approach, chambers, sap flow systems, and weighing lysimeters, are time-consuming and labour-intensive [4]
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