An assessment of reservoir filling policies and downstream impacts under a changing climate:

Ethiopia’s Grand Renaissance Dam

Ying Zhang, Paul Block,

Michael Hammond, Andrew King

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Outline

• The Nile Basin and The Grand Ethiopian Renaissance Dam

• Model Framework for Streamflow Simulation – Time-series Development

– Filling Policy

– Climate Change Scenarios

• Modeling Results and Analysis on Potential Downstream Impacts

• Future Work

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The Grand Ethiopian Renaissance Dam (GERD)

• Reservoir capacity of 74 bcm, 6000 MW of power generation

• Construction period:

2011-2017 (expected)

• Benefits – A developing country with rapidly

growing population

– Provide electricity

– Climate and hydrology variability

– Flood/drought control

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Malakal

Dinder-Rahad

Atbara

Khartoum

Lake Nasser

GERD

• Concerns from downstream countries, primarily Egypt

• Potential impacts of GERD, particularly during filling stage

• Climate variability and change add additional uncertainty

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Malakal

Dinder-Rahad

Atbara

Khartoum

Lake Nasser

GERD

The Grand Ethiopian Renaissance Dam (GERD)

Model Framework

• Simulate streamflow at Lake Nasser from 2011 to 2060

• Hydrology model: variation of Water Balance Model (WatBal) (Yates, 1996)

• The GERD hydropower and reservoir model

• Climate change and variability

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White

Nile

Malakal

Lake

Nasser

Tamaniat

Hasanab

Dongalla

Khartoum

Blue Nile

(GERD)

Dinder-

Rahad

Atbara

Modeled

Basin

Reservoir

Linear

losses

5 Filling Policies

• 3 policies consider fractions of total monthly streamflow entering the reservoir, impounding 5%, 10%, or 25%.

• 2 additional policies have retention rates contingent on the historical average streamflow (HASF) under a no climate change scenario – retain any quantity

greater than the

historical average

streamflow or 90%

of it (> 0.90*HASF)

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Monthly Streamflow

retention Storage

Flow out

of GERD

nET

Climate Change

• 8 Scenarios: – Temp. : GCMs consistently indicate an increase (+2.5 Celsius)

– Precip. : trends varying linearly from no precipitation change in 2011 to -20% ~ + 20% by year 2060;

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GCM precipitation projections and PDF of percent change in 2060.

Data & Time-series Development

Stream flow

Monthly Precipitation

Daily Mean Temperature

Diurnal Temperature

Range

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• 50 years of 1951-2000 CRU data to simulate streamflow from 2011 to 2060

• Bootstrapping 50-year time-series from historical data

• Streamflow outputs for each filling policy imposed with climate change scenarios

Model input and output

Modeling results under different filling policies

• FSL are never reached under 5% FP

• Large variation under >HASF FP

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Time to Reach FSL

Modeling results under different filling policies

• One selected simulation

• Large Reduction under >HASF FP, but actual leaving flow close to HASF

• Defining the filling stage as 15 years (2017-2032) 10

Percent reduction in SF at Lake Nasser

Modeling results for percent change in streamflow

filling

policy

2017—2032 2017—2022

Precipitation Trend, temp all +2.5 C

-20% 0 +20% -20% 0 +20%

5% -10.5% -2.7% 5.5% -8.0% -3.1% 2.0%

25% -15.2% -7.0% 1.6% -18.1% -13.9% -9.1%

>HASF -12.2% -6.2% 1.8% -10.3% -7.3% -4.6%

No Dam -8.1% 0.0% 8.6% -6.6% 0.0% 7.0%

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• Compare 25% and >HASF FP, similar over wet year for longer period

• Time required to fill the reservoir is different for each FP

• percent reduction over a shorter period shows more variability across different filling policies.

Median of Percent Change in SF at Lake Nasser

Modeling results for percent change in streamflow

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GCM precipitation projections and PDF of percent change in 2060.

Modeling results for percent change in streamflow

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Percent change of SF for weighted precipitation changes

Future Work

• Extending the model to demonstrate more specific downstream impacts

– the effect of the filling policies on Lake Nasser operations

– economic analysis from the perspectives of both Ethiopia and Egypt

• Additional basin development

– Irrigation, dam construction

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References Block, P. & Strzepek, K., 2012. Power Ahead: Meeting Ethiopia’s Energy Needs under a Changing Climate. Review of Development Economics, 16(3), 476–488. Block, P. & Strzepek, K., 2010. Economic analysis of large-scale upstream river basin development on the Blue Nile in Ethiopia considering transient conditions, climate variability, and climate change. Journal of Water Resources Planning and Management, 136(2), 156–166. Block, P., & B. Rajagopalan, 2009. Statistical-Dynamical Approach for Streamflow Modeling at Malakal, Sudan, on the White Nile River. Journal of Hydrologic Engineering, 14(2), 185-196. Conway, D., 2005. From headwater tributaries to international river: observing and adapting to climate variability and change in the Nile basin. Global Environmental Change, 15(2), 99–114. Conway, D. 2000. The climate and hydrology of the Upper Blue Nile, Ethiopia. Geographical Journal, 166, 49-62. Giannini, A., Biasutti, M., Held, I. & Sobel, A. 2008. A global perspective on African climate. Climate Change, 90, 359-383. Hargreaves, G.H. & Samani, Z.A. 1982. Estimating potential evapotranspiration. Journal of the Irrigation and Drainage Division, 108, 3, 225-230. Harris, I., Jones, P.D., Osborn, T.J., & Lister, D.H., 2013. Updated high-resolution grids of monthly climatic observations. In press, Int. J. Climatol., Doi: 10.1002/joc.3711 King, A. & Block, P., An assessment of reservoir filling policies under a changing climate for Ethiopia’s Grand Renaissance Dam. In review. Sutcliffe, J., & Parks, Y. 1987. Hydrologic modeling of the Sudd and Jongeli Canal. J. Hydrol. Sci., 32(2), 143–159. Yates, D. & Strzepek, K. 1998. Modeling the Nile Basin under climate change. Journal of Hydrologic Engineering, 3, 2, 98-108. Yates, D. 1996. WatBal: An integrated water balance model for climate impact assessment of river basin runoff. International Journal of Water Resources Development, 12, 2, 121-139.

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• Ying Zhang PhD Candidate at University of Wisconsin-Madison

zhang268@wisc.edu

• Advisor: Paul Block Assistant Professor at University of Wisconsin-Madison

pblock2@wisc.edu

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