Abstract
Abstract. The Upper Blue Nile basin is one of the most data-scarce regions in developing countries, and hence the hydrological information required for informed decision making in water resource management is limited. The hydrological complexity of the basin, tied with the lack of hydrometeorological data, means that most hydrological studies in the region are either restricted to small subbasins where there are relatively better hydrometeorological data available, or on the whole-basin scale but at very coarse timescales and spatial resolutions. In this study we develop a methodology that can improve the state of the art by using available, but sparse, hydrometeorological data and satellite products to obtain the estimates of all the components of the hydrological cycle (precipitation, evapotranspiration, discharge, and storage). To obtain the water-budget closure, we use the JGrass-NewAge system and various remote sensing products. The satellite product SM2R-CCI is used for obtaining the rainfall inputs, SAF EUMETSAT for cloud cover fraction for proper net radiation estimation, GLEAM for comparison with NewAge-estimated evapotranspiration, and GRACE gravimetry data for comparison of the total water storage amounts available in the whole basin. Results are obtained at daily time steps for the period 1994–2009 (16 years), and they can be used as a reference for any water resource development activities in the region. The overall water-budget analysis shows that precipitation of the basin is 1360 ± 230 mm per year. Evapotranspiration accounts for 56 % of the annual water budget, runoff is 33 %, storage varies from −10 to +17 % of the water budget.
Highlights
Freshwater is a scarce resource in many regions of the world, and the problem continues to be aggravated by growing populations and significant increases in demand for agricultural and industrial purposes
The results of the study are organized as follows: firstly, we present the results for (1) precipitation, (2) evapotranspiration, (3) discharge and (4) total water storage; secondly, the JGrass-NewAGE system is used to resolve the water-budget closure at each subbasin, and the contribution of each waterbudget term is further is analyzed
The rainiest subbasins are in the southern part of the basin
Summary
Freshwater is a scarce resource in many regions of the world, and the problem continues to be aggravated by growing populations and significant increases in demand for agricultural and industrial purposes. Most of the countries within the basin, such as Egypt, Sudan, South Sudan, Kenya, and Tanzania, receive insufficient freshwater (Pimentel et al, 2004). Exceptions to this are the small areas at the Equator and the Upper Blue Nile (hereafter UBN) basin in the Ethiopian highlands, which receives up to 2000 mm of precipitation per year (Johnston and McCartney, 2010). In Ethiopia, UBN is inhabited by 20 million people whose main livelihood is subsistence agriculture (Population Census Commission, 2008). As the principal contributor (i.e., 51 % of discharge) to the main Nile Basin, UBN supports hundreds of millions of people living downstream, and it is referred to as the ”Water Tower” of northeastern Africa. UBN is a part of transboundary river, and its development and management require obtaining agreements between many national governments and non-governmental organizations, each in-
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