Comparison of Methods for Estimation of Regional Actual Evapotranspiration in Data Scarce Regions: Blue Nile Region, Eastern Sudan

Remote sensing techniques enable estimation of regional evapotranspiration (AE) over large areas instead of point calculation and it also saves resources otherwise invested in monitoring instruments. The aim of this paper is to compare actual evapotranspiration (AE) estimated using the remote sensing method, the modified Thornthwaite water balance method (WB), and the complementary relationship method (GG) in the Blue Nile, Eastern Sudan. The satellite based Surface Energy Balance Algorithm for Land (SEBAL) model is used with Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data to estimate daily AE. The WB method is used as benchmark data when comparing the three methods. The results show that: (1) In the dry season (November-April), the SEBAL and GG methods give higher values than the WB method; (2) during the rainy season (May-October), the three methods give comparable results, where there is better agreement between SEBAL and WB than between GG and WB; (3) the spatial distribution pattern of monthly AE estimated by the SEBAL method during the dry season is mainly determined by the land-use type and whether there is irrigation taking place or not. However, in the rainy season, the spatial distribution pattern of monthly AE is mainly determined by the seasonal spatial distribution pattern of rainfall in the region.