Nile water accounting — how much is water resources and use in the Nile basin?
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Nile water accounting — how much is water resources and use in the Nile basin?

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Poster by Mohamed, Y.A.; Molden, D. and Bastiaanssen, W. for: CPWF Nile Basin Focal Project Final Workshop, Dar es Salaam, Tanzania, 9 December 2009.

Poster by Mohamed, Y.A.; Molden, D. and Bastiaanssen, W. for: CPWF Nile Basin Focal Project Final Workshop, Dar es Salaam, Tanzania, 9 December 2009.

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Nile water accounting — how much is water resources and use in the Nile basin? Nile water accounting — how much is water resources and use in the Nile basin? Document Transcript

  • FU Berlin Improved Agricultural Water Management In the Nile Basin Nile Water Accounting: How much is water resources and use in the Nile basin? 1.  Introduction The Nile water accounting (WA) assesses availability and use of the Nile waters considering  all  water  supplies  (rainfall,  river  flows,  groundwater),  and  all uses  (rainfed agriculture,  wetlands,  irrigation,  pasture  land,  natural  cover  etc.).  The  computation  procedure  is  based  on  water  balance  principles,  utilizing  satellite  measurements  of rainfall  (P),  evapotranspiration (ET),  biomass  production  (Bio),  and  limited  ground  information  of  river  flows (Q). The derived results helps to identify opportunities and constraints for basin‐wide  water  management,  providing  insights  on  how  to  manage  water  better,  and  hints  to  guide  future analysis.  2. Materials and methods < 25 25 - 50 50 - 100 Water  use  in  the  Nile  basin  is  represented  by  15  100 - 200 200-400 land use and water use classes, aggregated into 3  400 - 600 600 - 800 water  management  categories:  natural  land  use  800 - 1000 1000 - 1200 1200 -1400 (NL), managed land use (ML) and managed water  1400 - 1600 >1600 use  (MW).    The  categorization  reflects  to  what  extent the Nile basin is regulated.   Spatio‐temporal variability of rainfall and potential evapotranspiration Rainfall is the main water supply, as there are no  inter‐basin  water  transfers.  Total  outflow  to  the  Mediterranean  Sea  was  estimated  as  the  closure  term  of  the  water  balance.  The  ratio  of  biomass  Natural land use Managed land use Managed water use production  to  evapotranspiration provides  an  Natural forest Forest plantation Irrigation indicator of water productivity.  Savannah Rainfed agricutlure Managed wetlands Desert Drinking water 15 land use and water use classes 3. Results P-ET= 81.4 P-ET= 5.0 P-ET= -57.4 The water accounting results over 1 km2 pixels,  aggregated to NL, ML, and MW for year 2007 is  Available flow= 76.6 shown  in  the  figures  and  charts.  Of  the    1745  km3 of  rainfall,  only  76.6  km3  (4%)  is  available  for  ΔS= 0.0 diversion.  The  total  ET  is  98%  of  the  total  water  supply  showing  that  the  Nile  is  nearly  a  closed  basin  with  little  opportunity  to  increase  diversions.  The  majority  of  ET  (85%)  is  consumed  by  Outflow = 29.0 Aquifer & reservoirs natural  land  use  85%  (forests,  savannah,  etc.  much  of  which  supports  livestock);  with  11%  Committed = 9.8 consumed by managed land use (mainly rainfed crops); and only 4% by managed water use (mainly  irrigation).  About  76%  of  the  total  ET  is  beneficial  (economical or  environmental),  and  only  24%  non‐beneficial largely as soil evaporation from different  land use classes.   5. Conclusion The analysis shows that irrigation is just a small piece of the water  use within the Nile basin. Rainfed agriculture (7% of area), produces  80%  of  the  biomass,  while  irrigated  land  (1.6%  of  area)  produces 20%. Opportunities  to  increase  water  productivity  without  influencing river  flows  lies  within  the  natural  land  use  (Savannah,  shrub  land,  forest, etc.), much of which supports livestock. The analysis shows  that there is scope for water productivity improvements, and scope  to convert non‐beneficial evaporation to productive transpiration. For more information contact: e‐mail address Y.Mohamed@unesco‐ihe.org