Application of AVHRR imagery and GRACE measurements for calculation of actual evapotranspiration over the Quaternary aquifer (Lake Chad basin) and validation of groundwater models

The paper presents an application of NOAA-AVHRR and GRACE data for studying the regional hydrogeology of the Quaternary aquifer in the Lake Chad basin. The actual evapotranspiration (ET) over the phreatic aquifer is computed using the S-SEBI algorithm and then compared to the ET estimates derived from the GRACE land water solutions. Both the GRACE solutions and the S-SEBI results are similar in description of the actual ET over the Lake Chad basin. AVHRR data helped to overcome non-uniqueness in the modelling of the piezometry anomalies. Particularly, in regional groundwater models, the Harr piezometric dome appeared to be an area of relatively high effective recharge, while the Chari-Baguirmi and the Kadzell piezometric depressions and Bahr-el-Gahzal were probably areas of excess ET over recharge.