The implications of climate change for water resource development in the Blue Nile River

November 27th, 2012

Matthew McCartney, International Water Management Institute, Laos

This article evaluates the impact of climate change on the performance of existing and planned irrigation and hydropower schemes in the Ethiopian portion of the Blue Nile River. The results show that climate change will constrain the technical performance of large reservoirs with knock-on effects for agriculture and electricity production. Against this background water resource development in the basin requires interventions that bolster resilience and water security. This requires much more systematic planning of water storage and greater cooperation between the riparian states.

The Blue Nile River is an important shared resource of Ethiopia, Sudan and, because it is the major contributor of water to the main Nile River, also Egypt. To date, in contrast to Sudan and Egypt, Ethiopia has utilized very little of the Nile water. This is partly because of its inaccessibility and partly because the major centres of population lie outside of the basin. However, this is likely to change in the near future. To drive economic development, the Ethiopian government plans to utilize Nile water resources for both irrigation and hydropower. Many large dams are planned, both on the main stem and on tributaries, to support hydropower and irrigation development. If all planned development occurs, large reservoir water storage will exceed 160,000 Mm3 (i.e. approximately 14x present levels and 3x the current mean annual flow at the Ethiopia-Sudan border), irrigation will exceed 360,000 ha (i.e. 23x present levels) and installed hydropower generating capacity will be in excess of 10,000 MW (i.e. 47x present levels).1

There is great uncertainty about the impacts of climate change in the basin and there have been few systematic studies of the possible implications for water resource development. This research was conducted to determine the impact of one specific IPCC climate change scenario (A1B)2 on the performance of existing and planned irrigation and hydropower schemes in Ethiopia and the implications for flows into Sudan. This scenario was selected simply because it is a mid-range scenario resulting in climate change that lies between that anticipated by other scenarios. As such, it is a relatively conservative, but not overly cautious, scenario.

Three computer models were used in combination. A dynamic regional climate model – COSMO-CLM (CCLM) – was used to determine climate projections for the basin for the period 1983-2100 with initial and boundary conditions set by the ECHAM-5 model.3 The outputs generated from CCLM (i.e. rainfall, temperature and potential evapotranspiration) were used as input to a hydrological model (SWAT) which was setup, calibrated and validated with observed climate and hydrological data.4 Land use was assumed constant throughout the scenario simulation. Results of the SWAT modelling (i.e. projections in river flow and groundwater recharge), in conjunction with projected water demand, were used as inputs to the Water Evaluation and Planning (WEAP) model5 which was used to evaluate the possible impacts on hydropower generation and irrigation.

There is great uncertainty on exactly which water resource schemes will be implemented in the basin in the future. Consequently, in order to systematically assess the impact of growing water demand on the basin’s water resources, four development scenarios were identified and modelled.

No development – this scenario simulated the basin in its natural condition without any development. It provided a baseline to enable the impact of only CC to be assessed.

Current development – this scenario simulated water resources development in 2010. In this scenario, irrigation and hydropower schemes were the ones that are currently operating.

Intermediate development – this simulated possible expansion of existing irrigation schemes, as well as new hydropower and irrigation schemes that are likely to start by approximately 2025.

Full development – this simulated expansion of the near-future schemes and additional new schemes that are likely to occur in the future (i.e. before approximately 2050).

Results indicate that changes in climate will affect both water availability and demand. Under the A1B scenario, in a natural situation (i.e. no development), flows increase slightly at the Ethiopia-Sudan border in the first half of the 21st century but decrease by 20%, in the second half of the century. Average annual irrigation water demand fluctuates but increases significantly, particularly in the second half of the century (Figure 1). The planned water resources development in the basin will cause an additional 2.6% decline in flows at the border in the second half of the century.

The anticipated changes in climate will have significant impacts on both hydropower generation and water supply to irrigation schemes. The model simulations indicate that approximately 90% of irrigation demand will be met and the hydropower generated will broadly match the potential until the middle of the 21st century. However, in the latter part of the century, in the Intermediate and Full Development scenarios, 40% or less of the total irrigation demand will be met and only approximately 60% of potential hydropower will be generated (Figure 2).

Although there remains great uncertainty about how climate change will impact the water resources of the basin it is clear that, under this mid-range scenario, increased water storage in large reservoirs increases the area of land that can be irrigated and the amount of electricity that can be generated but the performance of that development will be curtailed as a consequence of climate change. The changes are likely to have serious consequences for economic development, food security and poverty in the region. The impacts of harsher climate change – which is equally, and based on current emissions trends perhaps more, likely – would be even more severe.

Against this background, water resource development in the basin requires interventions that bolster resilience and water security. To moderate the negative impacts of climate change requires much better planning and management of water storage. In the Nile Basin, this requires much greater cooperation between riparian states. Careful consideration needs to be given to integrated, possibly transnational, storage ‘systems’ that maximize the benefits to be obtained from the complementarities of different storage options (e.g., surface water used conjunctively with groundwater). However, planning for climate change requires going beyond water alone to consider other sectors in the water-energy-food nexus.

References:

1. McCartney, M.P. and Girma, M.M. (2012) Evaluating the downstream implications of planned water resource development in the Ethiopian portion of the Blue Nile River. Water International 37(4) 362-379.

2. Intergovernmental Panel on Climate Change (IPCC). 2000. Emissions Scenarios. Summary for Policy Makers. A special report of IPCC Working Group III. 27pp.

3. Hattermann, F.K. (2011) Rethinking water storage in Su-Saharan Africa. Report on generation of regional climate scenarios. Potsdam Institute for Climate Impact Research (PIK), Potsdam, Germany. 27 pp.

4. Girma, M.M. 2011. Potential impact of climate and landuse change on the water resources of upper Blue Nile basin. PhD thesis. Department of Earth Sciences, Freie university of Berlin.

5. Stockholm Environment Institute (SEI). 2007. WEAP: Water Evaluation and Planning system – user guide. Stockholm Environment Institute, Boston, USA.

Matthew McCartney is a principal researcher specializing in water resources and wetland and hydro-ecological studies. Until the end of 2011 he was based in IWMIs office in Addis Ababa, Ethiopia. He is now IWMIs head of office in Vientiane, Lao PDR. His experience stems from participation in a wide range of research and applied projects often as part of a multi-disciplinary team. He was a steering committee member on the UNEP Dams Development Project and is currently a member of the Ramsar Science and Technical Review Panel.

The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.