| This paper presents the result of the regional coupled climatic and
hydrologic model of the Nile Basin. For the first time the interaction
between the climatic processes and the hydrological processes on the land
surface have been fully coupled. The hydrological model is driven by the
rainfall and the energy available for evaporation generated in the climate
model, and the runoff generated in the catchment is again routed over the
wetlands of the Nile to supply moisture for atmospheric feedback. The
results obtained are quite satisfactory given the extremely low runoff
coefficients in the catchment.
The paper presents the validation results over the sub-basins: Blue Nile,
White Nile, Atbara river, the Sudd swamps, and the Main Nile for the period
1995 to 2000. Observational datasets were used to evaluate the model results
including radiation, precipitation, runoff and evaporation data. The
evaporation data were derived from satellite images over a major part of the
Upper Nile. Limitations in both the observational data and the model are
discussed. It is concluded that the model provides a sound representation of
the regional water cycle over the Nile. The sources of atmospheric moisture
to the basin, and location of convergence/divergence fields could be
accurately illustrated. The model is used to describe the regional water
cycle in the Nile basin in terms of atmospheric fluxes, land surface fluxes
and land surface-climate feedbacks. The monthly moisture recycling ratio
(i.e. locally generated/total precipitation) over the Nile varies between 8
and 14%, with an annual mean of 11%, which implies that 89% of the
Nile water resources originates from outside the basin physical boundaries.
The monthly precipitation efficiency varies between 12 and 53%, and the
annual mean is 28%. The mean annual result of the Nile regional water
cycle is compared to that of the Amazon and the Mississippi basins. |