Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 10 4 2006 10.5194/hess-10-507-2006 http://www.hydrol-earth-syst-sci.net/10/507/2006/ http://www.hydrol-earth-syst-sci.net/10/507/2006/hess-10-507-2006.html http://www.hydrol-earth-syst-sci.net/10/507/2006/hess-10-507-2006.pdf 507 518 2006-07-10 New lessons on the Sudd hydrology learned from remote sensing and climate modeling Y. A. Mohamed yasir1@unesco-ihe.org H. H. G. Savenije W. G. M. Bastiaanssen B. J .J. M. van den Hurk UNESCO-IHE, P.O. Box 3015, 2601 DA Delft, The Netherlands IWMI Nile Basin and Eastern Africa Sub Region, P.O. Box 5689, Addis Ababa, Ethiopia Delft University of Technology, Stevinweg 1, 2628 CN Delft, The Netherlands ITC (currently with WaterWatch), Generaal Foulkesweg 28, 6703 BS Wageningen, The Netherlands KNMI, P.O. Box 201, 3730 AE De Bilt, The Netherlands Despite its local and regional importance, hydro-meteorological data on the Sudd (one of Africa's largest wetlands) is very scanty. This is due to the physical and political situation of this area of Sudan. The areal size of the wetland, the evaporation rate, and the influence on the micro and meso climate are still unresolved questions of the Sudd hydrology. The evaporation flux from the Sudd wetland has been estimated using thermal infrared remote sensing data and a parameterization of the surface energy balance (SEBAL model). It is concluded that the actual spatially averaged evaporation from the Sudd wetland over 3 years of different hydrometeorological characteristics varies between 1460 and 1935 mm/yr. This is substantially less than open water evaporation. The wetland area appears to be 70% larger than previously assumed when the Sudd was considered as an open water body. The temporal analysis of the Sudd evaporation demonstrated that the variation of the atmospheric demand in combination with the inter-annual fluctuation of the groundwater table results into a quasi-constant evaporation rate in the Sudd, while open water evaporation depicts a clear seasonal variability. The groundwater table characterizes a distinct seasonality, confirming that substantial parts of the Sudd are seasonal swamps. The new set of spatially distributed evaporation parameters from remote sensing form an important dataset for calibrating a regional climate model enclosing the Nile Basin. The Regional Atmospheric Climate Model (RACMO) provides an insight not only into the temporal evolution of the hydro-climatological parameters, but also into the land surface climate interactions and embedded feedbacks. The impact of the flooding of the Sudd on the Nile hydroclimatology has been analysed by simulating two land surface scenarios (with and without the Sudd wetland). 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