AB1A1B1

Climate Change Scenarios for Northwest Africafrom the Continental to the Catchment Scales

Climate Change Scenarios for Northwest Africafrom the Continental to the Catchment Scales

The results show:

Balancing water availability and water demand in the Ouémé catchment

Application of the WEAP model

Conclusions

S. Giertz 1, B. Diekkrüger 1, B. Reichert 2, B. Höllermann 1, G. Steup 1, A. Kocher, H. Paeth and M. Diederich 3

1Department of Geography, University of Bonn, Meckenheimer Allee 166, Bonn; 2Steinmann Institute of Geology, University of Bonn, Nussallee 8, Bonn; 3Meteorological Institute, University of Bonn, Auf dem Hügel 20, Bonn

Modelling the impact of climate changes on water cycle and water availability in the Ouémé catchment

The conceptual hydrological model UHP-HRU was validated for several sub-catchments of the Ouémécatchment. It shows good results for different time periods in catchments with different land use. After validating the model it was used for scenario modelling.

Capillary rise

Surface runoff

Percolation

Interception

Evapotranspiration

Interflow Infiltration Root zone

Base flowGroundwater zone

Unsaturated zone

Deep groundwater recharge

Catchment withsub-catchments

Modelling water availability for different climate scenarios

Climate impact on water availabilityAfter evaluation the downscaled climate data were used in the hydrologic model UHP-HRU to simulate the impact of climate change on water availability in the Ouémé catchment.

The water demand was calculated applying the three IMPETUS development scenarios:B1: Economic growthB2: Economic stagnationB3: Business as usual

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Simulated withobserved climatedata

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Renewable water resources Oueme catchment

The surface water and groundwater recharge results from the UHP-HRU model were used as input data for the WEAP ‘Water Evaluation and Planning’ system. Using this data in combination with the water demand, WEAP assesses the development of the unmet demand for the different scenarios and reveals hotspots of water scarcity. The figure below shows the unmet demand per user group. Due to a decrease of available surface water the unmet demand increases mainly for the surface water users like irrigation, livestock etc.

The regional model REMO is nested into the GCM ECHAM. With REMO the IPCC scenarios A1B and B1 are simulated for West Africa including the degradation assumed by FAO. The results of the REMO model show similar trends for the climate in West Africa:

• Decrease of mean annual precipitation • Increase of mean temperature

Change in rainfall 1960/2001 – 2030/2050

Concept of the model UHP-HRU

Downscaling:algorithm based on probability

matching+ physical term

+ stochastic term The resultsshow• decrease of

renewable annual water resources for both scenarios

• trend more distinct for the A1B scenario

• decrease of available and accessible groundwater for both scenarios

Results are availablefrom the Spatial Decision Support Systems (SDSS): Water availability in the Ouémé: BenHydro

Domestic, agri-cultural (irrigation, livestock) and industrial water demands were taken into account.

As shown in the figure the total water demand increases for all scenarios and is highest in B1 scenario due to higher economic growth.

Results are available from the Spatial Decision Support Systems (SDSS):Water Demand: BenEau

• Water shortages during the dry season• Low water yields in the fractured aquifer • Insufficient water supply and sanitation infrastructure• Poor drinking water quality• Institutional problems of water management• Overuse of groundwater in South Benin resulting in

saltwater intrusion

• Increased water demand for agriculture and households due to high population growth

• Impact of climate change on seasonal and total water availability in Benin

• Increased land use change which causes erosion andsoil degradation

• Remaining problems with infrastructure and management• Halving the water availability per person and year due to

population growth in about 20 years

Possible future developmentBenin’s future socio-economic and environmental changes will have an important impact on the water demand and availability in Benin. Major developments -aggravating the already difficult water situation- will be:

The current situationBenin is currently not suffering from water scarcity as the actual annual freshwater availability of 4000m³ is far above the critical limit of 1000m³/cap/y. However, the Beninese population is affected from many water related problems:

Rainfall Temperature

• PrecipMon: A satellite based monitoring tool to be operationalized at the

Results of PrecipMon

Modelling climate scenarios with a dynamical and statistical

downscaling approach

In order to use the results for hydrological modelling a statistical downscaling approach was used to create virtual station data for each rainfall station in Benin.Results are available from the Information Systems (IS):• PrecipInfo: an interactive database composed of

processed historic measurements, remote sensing data, and atmospheric models.

• For the assessment of environmental and socio-economic impacts on future water resources an interdisciplinary modelling approach is required.

• Downscaling of global climate scenarios for hydrological modelling was successfully carried out by a combination of dynamical and statistical downscaling.

• Future scenarios revealed a decrease of available water resources in the Ouémécatchment for surface and groundwater.

• The water balance model shows that the unmet demand will increase in future due to the decrease of water availability and increase of water demand.

• All results of the models will be available for stakeholders in Benin in user-friendly SDSS, which are integrated in the IMPETUS SDSS-framework.

• The SDSS can support the water management process in Benin by providing reliable data und future scenarios in an user-friendly way.

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Urban Rural Livestock Periurban Irrigation

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Water availability and water demand in Benin under changing environmental and socio-economic conditions

Water related problems in Benin

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Groundwater Storage A1B Groundwater Storage B1Groundwater Storage A1B (averaged over 12 month) Groundwater Storage B1 (averaged over 12 month)

Dynamic of accessible groundwater in the Ouémé catchmentUnmet water demand scenario B1 with climate scenario A1B

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Downscaled climate scenariosLower Ouéme

Observed A1B B1

Downscaled climate scenariosUpper Ouémé

Input for hydrologicmodelling

national weather service provides real time esti-mates of rainfall and other meteo-rological data

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Water Demand Scenario B1 Water Demand Scenario B3 Water Demand Scenario B2

Total water demand in the Ouémé catchment

A1B B1