A model for Evaporation and Drainage investigations at Ground of Ordinary Rainfed-areas

Abstract

Quantification of water losses through evaporation and drainage from bare soils in arid and semi-arid regions is very important for an effective management strategy to conserve soil water. In this study, a model for Evaporation and Drainage investigations at Ground of Ordinary Rainfed-areas (hereafter E-DiGOR) is presented. Daily potential evaporation ( E p) from bare soils was calculated using the Penman–Monteith equation with a surface resistance of zero. Actual soil evaporation ( E a) was computed according to Aydin et al. [Aydin, M., Yang, S.L., Kurt, N., Yano, T., 2005. Test of a simple model for estimating evaporation from bare soils in different environments. Ecol. Model. 182 (1), 91–105; Aydin, M., Yano, T., Evrendilek, F., Uygur, V., 2008. Implications of climate change for evaporation from bare soils in a Mediterranean environment. Environ. Monit. Assess. 140, 123–130]. Deep drainage ( D) was simply calculated by the mass balance, taking field capacity into account. In order to test the performance of the model mainly for drainage estimations, a micro-lysimeter-experiment was carried out under field conditions. The experimental terrain was nearly flat, with no appreciable slope. Estimated and measured water balance components such as actual evaporation ( R 2 = 91.4%; P < 0.01), drainage ( R 2 = 88.5%; P < 0.01) and soil water storage ( R 2 = 89.7%; P < 0.01) were in agreement. This agreement supported the model hypothesis, thus rendering the model useful in estimating soil evaporation, drainage and water storage in an interactive way with a few parameters. Once the estimated and measured data from the experiment had been compared for validation, simulations were carried out continuously for the period of 1994–2006 in a semi-arid environment of Turkey. E p rates were lower during the winter season because of the lesser evaporative demand of the atmosphere. However, E a rates were mainly found to be functions of the rainfall pattern, and presumably soil wetness in addition to atmospheric evaporative demand. D volumes below 120 cm soil depth were high during rainy months, with a peak in January. Annual E p varied between 850.6 and 909.8 mm during the period of 13 years. E a ranged from 248.0 to 392.9 mm with a mean annual value of 302.5 mm. D substantially varied inter-annually (150.5–757.4 mm) depending on the intensity and frequency of rainfall events and especially antecedent soil wetness. The next logical step in model development would be the inclusion of runoff for sloping lands.