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Water use accounting in the Volta basin

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Presented at the Pre-Forum BFP meeting, 7-8 November, 2008 in Addis Ababa, Ethiopia

Presented at the Pre-Forum BFP meeting, 7-8 November, 2008 in Addis Ababa, Ethiopia

Published in: Education, Technology, Business
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  • 1. Water use accounting in the Volta basin Basin Focal Project – Volta Devaraj de CONDAPPA Mac KIRBY Jacques LEMOALLE Mohammed MAINUDDIN IRD, Montpellier CSIRO, Canberra BFPs pre-forum Meeting 7-8 November 2008, Addis Ababa
  • 2. The Volta basin – Location 400,000 km². Transboundary basin shared by 6 countries.
  • 3. The Volta basin – Climate & Rivers system Rainfall gradient: • drier in the North, • wetter in the South. ⇒ upstream drier than downstream. 3 main rivers system: • 2 perennial, • 1 non-perennial. Downstream, Lake Volta: • largest man made lake, • 8,500 km². Based on data from the CRU Period 1980 - 2000
  • 4. The Volta basin – Aim of this work Aim: assess the Basin’s water resource: • how much water is received by the Basin? • Basin uses? • distribution? Tool: the Water Use Account Spreadsheet of Kirby et al. (2006), relevant for such a large basin.
  • 5. Input data Digital Elevation Model: • 19 sub-basins, • modelling entities. Meteorological data from the Climate Research Unit: • precipitations, • temperature. Observed river-flows: • at the outlet of the 19 sub-basins, • data from: Volta HYCOS, Monthly Discharge Data for World Rivers dataset.
  • 6. Input data – Landuse Agglomerated landuse categories ⇒ 2 main classes: • Dryland Grazing, • Rainfed Cropland. Errors in Rainfed Cropland ⇒ correction with national agricultural statistics. Adapted from AVHRR / USGS
  • 7. Calibration 2 steps for calibration over a given period: 1. Reproduce the total flow volume. 2. Reproduce the shape of the hydrogram. Quality of the calibration was estimated with the Nash- Sutcliffe coefficient. Difficulty in the Volta basin: observed flows are more or less available.
  • 8. Calibration 800 Bad 700 Observed flow Nash-Sutcliffe coefficient < 0 Flow (Mm3 / month) 600 Calculated flow Calibration period 500 1974 - 1983 400 300 200 100 30 000 0 Observed flow Calibration period Dec-73 May-79 Nov-84 May-90 Oct-95 Apr-01 25 000 1990 - 1999 Flow (Mm3 / month) Calculated flow Good 20 000 Nash-Sutcliffe coefficient = 86% 15 000 10 000 5 000 0 3 6 8 1 94 7 9 l-8 -8 -9 -8 -9 -9 n- p ar ar ec ec Ju Ju Se M M D D
  • 9. Results – Overview of the Water Resource Average values for the period 1990 – 2000.
  • 10. Results – Water Accounting (1000 mm/year) Average values for the period 1990 – 2000.
  • 11. Results – Water Accounting and Water Uses How to increase the Water Uses? Outflows underused in the Basin. But one should keep in mind that Outflows and Evaporation from Natural Vegetation have non-economic values (natural, cultural, religious). Here: how to increase Agricultural Evapotranspiration? • Reduce Outflows: Soil and Water Conservation techniques, (1000 mm/year) irrigation by development of Small Reservoirs. • Reduce Natural Evapotranspiration: increase agricultural lands. • Develop irrigation from groundwater.
  • 12. Continuation Uses and Allocation of outflows: • modelled with WEAP, • using river flows calculated by the Water Use Account Spreadsheet of Kirby et al. (2006), • e.g., trade-off between development of upstream Small Reservoirs and impacts on downstream flows, • presentation in the Science Topic 3 Session “Water benefits sharing for poverty alleviation and conflict management”.
  • 13. Devaraj de CONDAPPA devaraj.de-condappa@ird.fr Jacques LEMOALLE lemoalle@ird.fr Mac KIRBY mac.kirby@csiro.au www.waterandfood.org www.ird.fr

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