Abstract
Simple formulas for estimating annual actual evapotranspiration (AET) based on annual climate data are widely used in large scale applications. Such formulas do not have distinct compartments related to topography, soil and irrigation, and for this reason may be limited in basins with high slopes, where runoff is the dominant water balance component, and in basins where irrigated agriculture is dominant. Thus, a simplistic method for assessing AET in both natural ecosystems and agricultural systems considering the aforementioned elements is proposed in this study. The method solves AET through water balance based on a set of formulas that estimate runoff and percolation. These formulas are calibrated by the results of the deterministic hydrological model GLEAMS (Groundwater Loading Effects of Agricultural Management Systems) for a reference surface. The proposed methodology is applied to the country of Greece and compared with the widely used climate-based methods of Oldekop, Coutagne and Turk. The results show that the proposed methodology agrees very well with the method of Turk for the lowland regions but presents significant differences in places where runoff is expected to be very high (sloppy areas and areas of high rainfall, especially during December–February), suggesting that the proposed method performs better due to its runoff compartment. The method can also be applied in a single application considering irrigation only for the irrigated lands to more accurately estimate AET in basins with a high percentage of irrigated agriculture.
Highlights
Actual evapotranspiration is a crucial component of both water and energy balance, which plays a significant role in climate–soil–vegetation interactions [1,2]
In the case of large-scale applications, the problem of measuring evapotranspiration can be addressed by hydrological methods, which are based on various conceptual approaches such as assessing water balance components using physically-based hydrological models (e.g., SWAT, MIKE, etc.) [6,7], simplistic water balance models [3,8,9,10,11], or even more simple actual evapotranspiration formulas such as those of Oldekop [12], Coutagne [13], Turk [14], Bouchet [15,16], Budyko [17,18,19] or similar that provide relationships between annual actual evapotranspiration (AET), annual average precipitation and potential evapotranspiration or temperature
The proposed methodology for estimating actual evapotranspiration is based on the losses of water (LOSW) indices [30,31] that assess the intrinsic rates of annual water losses from surface runoff (LOSW-R) and percolation (LOSW-P) of a reference surface
Summary
Actual evapotranspiration is a crucial component of both water and energy balance, which plays a significant role in climate–soil–vegetation interactions [1,2]. It is an extremely complicated biophysical procedure since it is regulated by the combination of climate, soil, topography, vegetation type and density [3]. For this reason, its measurement is only feasible in small scale applications (e.g., by using weighing lysimeters) while it is practically and economically impossible over long periods of time in large scale applications [4]. The Budyko concept, which in reality is the evolution of the Oldekop concept [20], is the most widely used method, and many efforts have been made to improve its proposed framework and to understand how climate and catchment characteristics regulate the long-term average water balance [21,22,23,24,25,26,27,28,29]
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