Integrated management of the Blue Nile basin in Ethiopia: Precipitation forecast, hydropower, and irrigation modeling.

摘要

Ethiopia is at a critical crossroads with a burgeoning population, a severely depressed national economy, insufficient agricultural production, and a minimal number of developed energy sources. The upper Blue Nile basin harbors considerable untapped potential for irrigation and hydropower development and expansion, in addition to improvement in rain-fed agricultural production through precipitation forecasting. Integrated models are created to assess potential conditions and may serve as useful tools for agricultural and water resources planning and management within the basin. One-season lead predictors for forecasting of the Kiremt season precipitation are identified from the large-scale ocean-atmosphere-land system. A nonparametric approach based on local polynomial regression is proposed for generating ensemble forecasts. Cross-validated forecasts indicate significant skill in comparison to climatological forecasts, as currently utilized by the Ethiopian National Meteorological Services Agency. Numerous hydrologic models have been developed to assess hydropower and agricultural irrigation potential within the basin, yet often fail to adequately address critical aspects, including the transient stages of large-scale reservoirs, relevant flow retention policies and associated downstream ramifications, and the implications of stochastic modeling of variable climate and climate change. A hydrologic model with dynamic climate capabilities is constructed to assess these aspects. Scenarios incorporating transient conditions are found to typically produce smaller benefit-cost (b-c) ratios than non-transient scenarios by 0.2-0.8, equating to underestimations of 1-6 billion US dollars. Climate change scenarios indicate potential for small b-c increases, but reflect possible significant decreases. Stochastic modeling of scenarios representing a doubling of the historical frequency of El Nino events indicates b-c ratios near 1.0, with numerous runs producing smaller ratios or even potentially infeasible projects due to a lack of timely water. An evaluation of expected energy growth rates reinforces the need for significant economic planning and the necessity of securing energy trade contracts prior to extensive development. A preliminary extension model to Dongola, Sudan, including a dynamical-statistical model of White Nile streamflow, illustrates an average 2-3% reduction in annual streamflow for a 5% annual streamflow retention policy within Ethiopia.