P25 AB1 A1 B1 Climate Change Scenarios for Northwest Africa Climatefrom the Change Continental Scenarios to the for Catchment Northwest Scales Africa Assessing waterfrom use, the groundwater Continental availability to the and Catchmentsoil salinity in theScales Middle Drâa basin S. Klose 1, A. Klose 2, C. Rademacher 3, H. Busche 2, O. Schulz 2 and B. Reichert 1, B. Diekkrüger 2, M. Rössler 3 1 Steinmann Institute - Geology, University of Bonn, Nussallee 8, Bonn 2 Institute of Geography, University of Bonn, Meckenheimer Allee 166, Bonn 3 Institute of Cultural and Social Anthropology, Albertus-Magnus-Platz 1, Cologne. Introduction Support for solutions Availability and quality of surface water from the upstream reservoir Mansour Eddahbi and individually • Interdisciplinary work provides: pumped groundwater determine irrigation within the six Drâa oases. - Assessment of surface water availability from the reservoir Mansour Eddahbi In order to cover the irrigation demand more and more alluvial aquifers are tapped which are located - Assessment of domestic water consumption beneath each oasis. - Assessment of crop water demand Problems: - Groundwater balance modelling • Water scarcity and soil salinity restrict agricultural production - Soil salinity modelling • Recurrent droughts, unplanned groundwater mining, groundwater and soil salinity as well as • The developed Spatial Decision Support System IWEGS provides system analysis and population growth and urbanization are the major problems. the simulation of management options concerning groundwater and soil. Domestic water use The modelling approach considers: Surface water availability Mm³ / a Inhabitants urban water consumption Mm³ / a 1 70000 • Releases from the reservoir Mansour Eddahbi, so-called Lâchers (fig. 1.) rural water consumption Supposed annual outlet (ORMVAO, 1995) 700 0.9 urban population 60000 90 % quantile 0.8 rural population • Groundwater availability (model BIL, fig. 2) based on water extraction and 600 10 % quantile 0.7 50000 groundwater recharge 0.6 40000 500 0.5 • Soil and groundwater salinity (model SahysMod) based on salt balances 30000 0.4 for groundwater and soil depending on agricultural techniques and climatic 400 0.3 20000 conditions (fig. 5 & 6) 0.2 300 10000 0.1 • Specific crop water demand calculated by the model Cropwat (FAO) and 200 0 0 Mezguita Tinzouline Ternata Fezouata Ktaoua M'Hamid further processed to the scale of the oases (fig. 7 & 8) 100 Fig. 9.: Domestic water consumption (2000) accounts only to a • Domestic water consumption estimated for rural and urban population minor fraction of the total water demand, whereas the distinctively (fig. 9) based on demographic projections 0 consumption of the urban population is disproportional high in comparison to the rural population (cp. P21). 73/74 75/76 77/78 79/80 81/82 83/84 85/86 87/88 89/90 91/92 93/94 95/96 97/98 99/00 01/02 Fig. 1.: Releases from the reservoir Mansour Eddahbi depend on the filling level and show high inter-annual variability. The aim of an annual outlet of 250 Mm³ was reached in only 43 % Crop water demand of years (cp. P23 & P24). Mm³ / a ha 50 Total water demand 8000 Cultivated surface Groundwater availability 40 6000 + Recharge by infiltration of - Extraction for irrigation es river water (Lâcher) 30 Dad Ouarz + Recharge by rain infiltration - Extraction for domestic and azate 4000 Reservoir Mansour Eddahbi (sub-basin tributary to aquifer) drinking water supply Ouarzazate + Recharge by irrigation return - Evaporation from river water 20 flow from river water (Lâcher) (during Lâchers) + Recharge by irrigation return - Evaporation (indirectly by Reservoir Agdz 2000 Mezguita flow from pumped recharge coefficients) 10 Reservoir Tansikht groundwater Agdz 0 0 + Groundwater afflux Mezguita Tinzouline Ternata Fezouata Ktaoua M'Hamid Agricultural Tinzouline Reservoir Ifly from upstream (1D flow by Darcy law) - Groundwater discharge Fig. 8.: Average annual crop water demand and size of Ouled Yaoub towards downstream cultivated area of the oases (2001-2006) depend on crop production and Ternata (1D flow by Darcy law) compilation and climatic conditions. Zagora Fezouata Fig. 2.: Items of the groundwater budget for the Drâa oases domestic water use implemented in the model BIL (cp. P20). 250 D r in the oases depend â a Reservoir Azaghar 200 Lâcher Henna Ktaoua Recharge volume on a number of Surface of the Alfalfa coefficient = 160 Mm³ 150 basin = 1,273 km² Vegetables = 3 % Bean constrains Reservoir Bounou Mais 100 mmm²* month / Barley Kilometers Wheat 0 510 20 30 40 M‘Hamid 50 Recharge Recharge coefficient coefficient = 10 % = 10 % 0 Jan Fev Mar Avr Mai Jun Jul Aou Sep Oct Nov Dec Fig. 7.: Average monthly water demand of the main crops for the oasis Mezguita (2001-2006). Aquifer thickness = 25 m Initial saturated thickness = 10 m K = 7 · 10 -3 m/s Initial groundwater volume = 659 Mm³ Specific Yield = 10 % Soil salinity Fig. 3.: Parameters for the groundwater balance (model BIL) of the year 1973 at the oasis Tinzouline. 100 1968 measured 90 1980 measured irrigation 1980 modelled evapotranspiration 1998 modelled 100 80 Tinzouline modeled 90 soil ∆∆∆ soil reservoir 70 canal Tinzouline observed losses 80 60 capillary rise percolation 70 transition reservoir 60 50 transition ∆∆∆ zone 50 40 40 % of % theoases surface 30 seepage percolation 30 Filling level of aquifer [%] aquifer of level Filling 20 20 aquifer ∆∆∆ aquifer reservoir 10 10 0 0 pumping 0-4 4-8 8-16 16-32 > 32 73/74 75/76 77/78 79/80 81/82 83/84 85/86 87/88 89/90 91/92 93/94 95/96 97/98 99/00 01/02 03/04 05/06 07/08 09/10 11/12 13/14 15/16 17/18 19/20 21/22 23/24 Salinity class [mS/cm] p.e. faults Hydrological year Fig. 6.: Comparison of measured (1968, 1980) and modelled Fig. 5.: Concept of the model SahysMod for calculating water Fig. 4.: Filling level of the aquifer of Tinzouline from 1973/74 to 2024/25, modelled (SahysMod) soil salinity (1980, 1998) for the oasis Mezguita and salt balances. (light blue) and observed (dark blue). Beyond the red line the input data for the (cp. P20 & P27). Lâchers is extrapolated (cp. P24)..