identifying suitable areas for water harvesting in the upper blue nile basin, ethiopia - yihun dile,...
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Identifying suitable areas for water harvesting in the Upper Blue Nile Basin, Ethiopa
Authors: Yihun Dile Taddele, Louise Karlberg, Johan RockströmStockholm Environment Institute
Pitting Strip catchment tillageMeskat-type system
What are they?Contour bunds
Semi-circular bunds
Floodwater harvesting within the stream bed Ephemeral Stream Diversion
Hillside sheet/rill runoff utilization
Dry spells
Flooding
Drought
Land degradiationWhy Water Harvesting
Then what?
- with water harvesting- without water harvesting
Bridging dry spells and droughts, and creats a resilient farming system which can produce more crop per drop
Avoid flooding problems by flattening the hydrograph: Ex-situ water harvesting Supports a sustained stream flow downstream: both in-situ and ex-situ
Improves soil fertility
BUT?
Precipitation DEM Land Cover Soil
Surface Analysis
Slope map Land coverrastar map
Land coverrastar map
Vector to grid conversion
ReclassifiedPrecipitation
Reclassified slop map
Reclassified land cover
ReclassifiedSoil
Reclassifying into 5 classes
WH suitability maps
Weighted Overlay Analysis
Suitability Criteria
Suitability values 1 2 3 4 5 Precipitation(mm) <200 >1200 200-400 800-1200 400-800Slope(%) >20 12-20 8-12 2-8 <2 Land cover Bushland, forest N.A N.A plantations cultivated land woodland, grassland irrigated land swamp, shurbland
Soil Leptosols Arenosols Vertisols Luvisols, Cambisols Regosols Acrisols, Alisols Fluvisols, Nitisols
Percent Influence Assignment
Percent Influence
Parameter
Precipitation
Slope
Land use
Soil
Condition - 1
25
25
25
25
Condition - 2
30
30
20
20
Condition - 3
35
25
20
20
Condition - 4
25
35
20
20
Condition - 5
35
30
20
15
S = ∑wi*xi
S = final suitability score; wi is weight of factor i and xi is the criterion score of factor i
Suitability Analysis
Equal inflience assignment for precipitation, slope, land use and soil
30% influence assignment for Precipitation & slope, and 20% for land use & soil
Results
35%, 25%, 20% and 20% influence assignmentFor precipitation, slope, land use & soil resp.
25%, 35%, 20% and 20% influence assignmentFor precipitation, slope, land use & soil resp.
Results
Results
Suitability level
Condition-1
Condition-2
Condition-3
Condition-4
Condition-
5
5 0 0 0 0 0
4 23 11 8 10 6
3 57 61 61 62 61
2 16 23 28 23 29
1 0 1 0 1 0
% precipitation slope
Discussion and conclusion
The Upper Blue Nile has a large potential for water harvesting: 6% to 24%, most suitable and over 50% moderate suitability
The results of the study are highly sensitive to precipitation amounts
If higher value is given for other land use types such as open woodland, the potential suitable area will increase considerably
soil type: Luvisols, Cambisols, Vertisols increases water avilability for livestock – increases farmers tendency to invest in agriculture – which has nexus effect on increasing on water productiity
Thank You
Questions?