Supporting water management in the Volta river basin
with Water Accounting Plus (WA+)
References:
[1] www.wateraccounting.org [2] Mul et al., 2015. Water resources assessment of the Volta River Basin. IWMI Working Paper 166. doi: 10.5337/2015.220
[3] Data sources: Globecover 2009; GFSAD Crop Mask 2010; World Database on Protected Areas; Evapotranspiration products (GLEAMv3) ; Rainfall products (RFEv2). [4] Budyko, M. (1974). Climate and Life, 508 pp: Academic Press, New York.
Acknowledgement: This project is supported by the Swiss Confederation and the Swiss National Science Foundation (SNSF).
Moctar Dembélé
1,2, Bettina Schaefli
1, Grégoire Mariéthoz
1, Natalie Ceperley
1, and Sander J. Zwart
31
Institute of Earth Surface Dynamics, Faculty of Geosciences and Environment, University of Lausanne, Switzerland
2Water Resources Section, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Netherlands
3
Natural Resources Department, Faculty of Geo-Information Science and Earth Observation, University of Twente, Netherlands
3. First Results
5. Next steps
1. Background/Objectives
2. Method/Materials
4. Summary/Discussion
Uncertainty in water availability in declining rainfall areas
Reliable water resources assessment
Better planning & management
Fig.1: Volta river basin in West Africa
Objective: Provide information on water accounts to support the development and implementation of sustainable water use policies and management strategies.
moctar.dembele@unil.ch
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Study area: Volta River
basin (VRB) (Fig.1) Area ≈ 410,000 km2 semi-arid - sub-humid climate South-North gradient of increasing aridity 6 riparian countries Different national
priorities for water use Water uses: Hydroelectricity Irrigation Aquaculture Domestic use Key challenges [2]: Water quantity &
seasonal flows Ecosystems degradation Water quality Climate change Governance
Current and Future state of water accounts?
WA+: Independent estimates and summary of complex hydrological processes (flows,
fluxes, stocks, storage changes and consumptive use) in river basins [1].
Based on 4 types of land/water use:
Protected Land Use (PLU): no possible/advisable changes in land/water management.
Utilized Land Use (ULU): irregular vegetation management and limited human influence. Modified Land Use (MLU): vegetation/soils are managed, natural water supply (rainfall). Managed Water Use (MWU): sectors withdrawing water from surface/groundwater.
Key bio-physical levers driving water productivity? How do we increase beneficial and managed
fractions of ET?
Is “non-beneficial” ET a loss?
Sensitivity of the WA+ to input data?
Contribution of WA+ to the UN SDGs (Goal 6)? Linking hydrological modelling
& WA+ for future projections
Evapotranspiration Sheet: understanding how, where and when water is consumed,
and relate water consumption to intended purposes (beneficial vs. non-beneficial ET)
Resource Base Sheet: overview on over-exploitation, unmanageable, manageable,
exploitable, reserved, utilized and utilizable flows at river basin scale.
ET T ET T Grasslands 8.69 7.15 38.0 32.3 Shrublands 18.84 16.16 Water Bodies 0.02 0.01 Bare Areas 0.72 0.41 37.7 Forest 2.71 2.34 Grasslands 36.02 28.19 161.5 131.5 Shrublands 119.33 99.36 14.5
Rainfed Croplands 77.43 63.45 248.3 Environment 128.2 99.6 82.2 Urban Areas 0.10 0.07 Economy 11.2
Leisure 12.3 38.0 Water Bodies 5.69 1.17 7.1 2.3 106.9 Energy 6.1 Managed 106.7 22.10 18.68 Modified Land Use 8.92 Protected Land Use Managed
Water Use Irrigated Croplands 1.38 Bare Areas 0.02 2.70 To ta l E va p o tr an sp ir ati o n 306.1 161.5 Manageable Non-Manageable Non-Beneficial 41.4 5.7 Agriculture Beneficial 264.7 57.9 Eva p o ra ti o n In te rce p ti o n 1.11 Water Bodies Tr an sp ir ati o n W ate r Utilized Land Use Soil 1.21 Forest Woodland 0.01 Forest 10.38 Units [km3/year]
Note: All results are for 2008
Budyko Curve [3], [4]:
describes partitioning of P into ET and Q (y-axis), and deviation in climatic conditions (x-axis).
Used to check the
accuracy of the LULC
classes and for Green and Blue water assessment.
𝐸𝑇
𝑃 = Φ tanh Τ1 Φ 1 − 𝑒
−Φ 0.5
Φ = 𝑃𝐸𝑇 𝑃Τ
Annual ET breakdown Beneficial ET breakdown
WA+ Land Use map [3]:
-PLU: wetlands, national parks, RAMSAR sites, etc. -ULU: natural pastures, savannas and deserts, woodlands, lakes, etc. -MLU: built-up areas,
rainfed croplands, timber plantations, etc.
-MWU: irrigation, urban water supply, industrial extractions, dams, etc.
Data sources: + Remote sensing + Public domain + Geoportals Results summarized: In 8 sheets (Fig.2) with key indicators
Budyko framework used for plausibility analysis
Fig.2: Simplified WA+ flow chart
Protected Land Use 36.4
338.5 Utilized Land Use 155.9 323.1 Modified Land Use 94.9
Managed Water Use 5.4
45.8 34.3 30.5 Protected Land Use 3.1 14.0 Manmade 1.7
Padvection Utilized Land Use 12.0 Natural 12.3 245.3
Modified Land Use 8.3 Other 0.0
Qdesal Managed Water Use 7.1 16.5 31.8
QSWin 15.3 QGWin 0.0 0.0 + ∆S 0.0 Ex ter n al 351.2 G ro ss i n fl o w N et i n fl o w 74.1 277.1 QSWoutlet QSW out QGW out Ou tf lo w D ep let ed w at er ET Ex ter n al Precycled 61.3 61.3 ETrecycled 245.3 31.8 C o n su med w at er N o n -co n su m ed w at er 351.2 0.0 0.0 Incremental ET Ex p lo it ab le w at er Av ai lab le w at er Uti liz ed fl o w -Committed outflow Reserved outflow, max. of -Navigational outflow -Environmental outflow Lan d sc ap e E T 292.6 412.5 2.6 8.9 292.6 R ai n fal l ET Utilizable outflow Non-Utilizable outflow Non-recoverable flow 3.8 Units [km3/year]
