Determination of groundwater evapotranspiration at regions with shallow water table (Case study: Azadegan plain, Iran)

Evaporation is a major phenomenon that water wastes from the ground surface, depends on some important factors e.g. availability of water, energy (sunshine and wind) and also evaporative surfaces. In cases where the ground water rises upward and/or is almost near to the surface, ground water evaporation would naturally accelerated due to the availability of water resource, especially in arid and warm conditions. Main objective of this study was to determine the volume of water wasted from the ground surface in cases where the ground water is shallow. Since the groundwater depth in Azadegan plain, Khuzestan province, Iran, is low (between 0.4 to 4 m below the surface), and also its climatic condition is generally agree with evaporation, therefore, it is anticipated that a large volume of this water would be wasted via the phenomenon. On the other hand, different transpiration surfaces such as native vegetation and agricultural lands almost exist in the area. Therefore, evapotranspiration (ET) of the land and its vegetative cover would be the major way for water wasting in the region. To have an estimation of the volumetric wasted water in the region, a seasonal time series of MODIS satellite images (2007 to 2008) and also ancillary climatic data were acquired for determination of ET via Surface Energy Balance Algorithm for Land (SEBAL). The results of this study show the adequacy of the method for estimation of actual ET at regions with shallow ground water table. Based on the results, actual evapotranspiration of waterlogged areas is about 1.5 fold of agricultural lands and about 3 fold of bare soils. Also ET of waterlogged areas is about 30% of potential evapotranspiration at the studied region.

کلیدواژه ها:

Evapotranspiration ، SEBAL ، shallow groundwater ، Azadegan plain.