Mapping Irrigation Potential from Renewable Groundwater in Africa: A Quantitative Hydrological Approach

Mapping Irrigation Potential from Renewable Groundwater in Africa: A Quantitative Hydrological Approach

Yvan Altchenko & Karen G. Villholth

Phot

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Ste

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/ IW

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o Background Huge GW volumes in Africa (MacDonald et al, 2012) but not all

available for abstraction, and unevenly distributed

1 % of cultivated land is equipped for irrigation with GW while it is 14% in Asia, which has similar climate (Siebert et al., 2010)

Only approx. 2 mill. ha irrigated with GW presently

Groundwater provides an important buffer to climate variability and change

o Questions Where is the GW irrigation potential (GWIP) in Africa? How much cropland can GW irrigate?

o Objective To estimate the cropland area that renewable GW can irrigate in Africa (using Pavelic’ et al. (2012) water balance

approach)

o Some assumptions in computations GW is the only water source for irrigation (no conjunctive use with SW) GW is usable and accessible (no quality, yield, or socio-economic constraints) GW is locally available

(106 ha)

Asia Africa0

100

200

300

400

500

600

Cultivated land Total area equipped for Irrigation Area equipped for ir-rigation irrigated with groundwater

Methodology

o Hydrological data• Recharge• Water available for crop from rain (green water)

o Other GW uses• human activities (domestic, livestock, industrial)• environment

o Crop data• Surface of cropland• Crop distribution• Crop water demand• Irrigation efficiency

𝑮𝑾 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆=𝐺𝑊 h𝑅𝑒𝑐 𝑎𝑟𝑔𝑒 –𝐻𝑢𝑚𝑎𝑛𝐺𝑊 𝐷𝑒𝑚𝑎𝑛𝑑 – 𝐸𝑛𝑣𝑖𝑟𝑜𝑛 .𝐺𝑊 𝑅𝑒𝑞 .

Different geographical data compiled in GIS

n= crop

Cell size : 0.5 x 0.5 degree(≈ 50 km x 50 km)

Hydrological data

from the PCR-GLOBWB model (Utrecht University, the Netherlands, Wada et al., 2011)• Leaky bucket type of model, applied on a cell-by-cell base• cell size of 0.5 x 0.5 degree ≈ 50 x 50 km• Daily step time• Data from 1960 to 2001

(41 years)

QDR = Direct RunoffQSf = InterflowQBf = baseflowStore 1 = soil 1 (0 – 0.3 m deep)Store 2 = soil 2 (0.3 – 1.2 m deep)Store 3 = GW storage

Green water (monthly value) = Transpiration from soil 1 + soil 2

Recharge (annual value)

Methodology

Other GW uses• Human activities from FAO (geonetwork) using density of population and livestock

• Environmental water need according to three different scenarios:• Scenario (a) : 70 % of recharge goes to environment• Scenario (b) : 50 % of recharge goes to environment• Scenario (c) : 30 % of recharge goes to environment

Methodology

Uses/unitDaily water need

(L)Portion assumed to come from GW

(%)

Domestic Inhabitant 50 75

Industrial Inhabitant 25 75

Livestock

Big ruminant 40 100

Small ruminant 20 100

Pig 30 100

Poultry 0.2 100

Groundwater Availability

Annual calculations over 41 years, then average

From 692 to 1644 km3 available for irrigation per year, depending on scenario

Average groundwater availability for irrigation (1960–2000), expressed in 106 m3 year−1 cell−1 (0.5° ×0.5°)

𝑮𝑾 𝑨𝒗𝒂𝒊𝒍𝒂𝒃𝒍𝒆=𝐺𝑊 h𝑅𝑒𝑐 𝑎𝑟𝑔𝑒 –𝐻𝑢𝑚𝑎𝑛𝐺𝑊 𝐷𝑒𝑚𝑎𝑛𝑑 – 𝐸𝑛𝑣𝑖𝑟𝑜𝑛 .𝐺𝑊 𝑅𝑒𝑞 .

3 scenario: environmental groundwater requirements as 70 % of recharge 50 % of recharge 30 % of the recharge

Crop data

• Cropland area: Crop distribution from Center for Sustainability and the Global Environment (SAGE), University of Wisconsin, Madison, Wisconsin, USA

• World map• Resolution: 5 minutes• 11 major crops • Geographic crop distribution for the year 2000

• Crop water demand from compiled FAO database

Monthly crop water demand calendar for 6 crop groups

Methodology

Proportion of cropland per cell (0.5° x 0.5°) in 2000

Monthly crop water demand based on

With maximum reference evapotranspiration for each calendar month

• Length of crop growth stage (initial, development, mid-season, end)

• Crop coefficient for crop growth stage (Kc initial , Kc development , Kc mid-season , Kc end )

Example: tomatoes• Single crop coefficient and growing length

• Calculation of monthly crop coefficient

• Planting and harvesting calendar

Growing stage initial development mid-season end

Growing length (days) 35 45 40 25

Crop coefficient 0.45 0.75 1.15 0.8

Month 1 2 3 4 5

Water need (mm) 0.45 0.7 0.88 1.15 0.67

Methodology

Zone code Zone name

Irrigation Efficiency

( %)1 Mediterranean coastal zone 602 Sahara oases 703 Semi-arid to arid savannah West-East Africa 504 Semi-arid/arid savannah East Africa 505 Niger / Senegal rivers 456 Gulf of Guinea 507 Southern Sudan 508 Madagascar tropical lowland 509 Madagascar highland 50

10 Egyptian Nile and Delta 8011 Ethiopian highlands 5012 Sudanese Nile area 8013 Shebelli-Juba river area in Somalia 5014 Rwanda - Burundi - Southern Uganda highland 5015 Southern Kenya - Northern Tanzania 5016 Malawi - Mozambique - Southern Tanzania 4517 West and Central African humid areas 4518 Central African humid areas below equator 4519 River affluents on Angola / Namibia / Botswana border 5020 South Africa - Namibia - Botswana desert & steppe 6521 Zimbabwe highland 6022 South Africa - Lesotho - Swaziland 6023 Awash river area 50

Irrigation cropping pattern zones and irrigation efficiency (FAO, 1997)

Methodology

Crop group coefficient per month

Example: zone 15 (en mm)Crop group Description Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

CerealsMaize/Rice/Sorghum 1.03 1.08 1.18 1.18 1.03 0.83

Maize/Rice/Sorghum 1.18 1.03 0.83 1.03 1.08 1.18

Oil cropsSunflower/Groundnut/Soybean 0.58 0.47 0.85 1.13 1.08

Sunflower/Groundnut/Soybean 0.47 0.85 1.13 1.08 0.58

RootsPotatoes 0.45 0.75 1.08 1.1 0.71

Potatoes 0.71 0.45 0.75 1.08 1.1

PulsesBean 0.2 0.47 0.83 1.1

Bean 0.47 0.83 1.1 0.2

VegetablesOnion/Tomato/Eggplant/Cucumber 0.53 0.74 1 1.13 0.65

Onion/Tomato/Eggplant 0.52 0.74 1 1.13 0.65

Sugarcane Sugarcane 0.4 0.9 1 1.13 1.25 1.25 1.25 1.25 1.25 1 0.75 0.88

Methodology

n= crop

(maximum reference evapotranspiration for each calendar month)

Monthly calculations, then sum to get annually irrigation water demand over 41 years

Average Net Irrigation Water demand (1960-2000)

Results

Cropland

Results

Total area irrigable with groundwater inside a cell (0.5° ×0.5°) in 103 ha

GWIP calculated annually, then averaged over 41 yearsGW Available entered as average over 41 years to consider buffer effect of GW

70 % of recharge to environment 50 % of recharge to environment 30 % of the recharge to environment

AFRICAEnvironmental requirements represent

30% of recharge 50% of recharge 70% of recharge

Area (106 ha) 105.3 74.9 44.6

% of cropland 48.5% 34.5% 20.5%

Proportion of cropland irrigable with groundwater

ResultsA factor of 20 increase in overall GWI possible (from 2 to ≈ 40 mill ha.)

70 % of recharge to environment 50 % of recharge to environment 30 % of the recharge to environment

Comparison with GW irrigated cropland in 2005 (Siebert et al. 2010)

Results

Area irrigated with groundwater in 2005 expressed in ha. per cell adapted from Siebert et al. (2010)

Groundwater irrigation potential for the year 2000 expressed as the percentage of the area irrigated with groundwater in 2005

scenario (b): 50 % of recharge goes to environment

Recharge• Uncertainty

Country

Recharge (mm/yr)

FAO, AQUAStat, 2009

Döll and Fiedler, 2008

This paper

Burkina Faso 34.6 39 39

Ethiopia 18.1 39 80

Ghana 110.3 105 127

Kenya 6.0 46 29

Malawi 21.1 164 170

Mali 16.1 22 23

Mozambique 21.3 104 82

Niger 2.0 12 4

Nigeria 94.2 163 154

Rwanda 265.8 68 78

Tanzania 31.7 93 90

Uganda 122.9 95 50

Zambia 62.4 108 117

Discussion

Recharge• Uncertainty• Variability

Discussion

both over the period 1960-2000 (data from Wada et al., 2011)

Average annual recharge (mm/year) coefficient of variation (%)

Recharge• Uncertainty• Variability

Groundwater available: • 3 scenarios (in km3 year-1)

Limitations of approach• Non-limiting condition for other fundamental physical properties

e.g. soil, water quality, terrain slope, groundwater accessibility, …• Socio-economics constraints

e.g. investment capacity, infrastructure, …• Groundwater irrigation potential for 2000

No consideration of climate change and population/livestock growth, change in cropping pattern, improvement in irrigation efficiency

Scenario 1 Scenario 2 Scenario 3

Min. Average Max. Min. Average Max. Min. Average Max.

442.2 692.1 990.1 751.1 1168.3 1664.9 1006.1 1644.5 2339.7

Discussion

A continental-scale distributed map of GWIP has been produced for the first time.

Is there potential for irrigation with groundwater in Africa?

• Yes, there is, up to a factor of 20 increase, relative to present GWI area (2 40 mill ha.)• Map shows large spatial variability across Africa, and even within countries• GWIP from renewable GW strongly related to GW recharge, cropland availability, and present

demand on GW• GWIP is particularly significant and relevant in the semi-arid Sahel and East African corridor,

especially for small-scale and smallholder irrigation, with huge poverty alleviation potential• In areas like Northern Africa and South Africa, GWIP from renewable GW has already been

exhausted• In central Africa, GWIP is huge, but largely irrelevant• Further research required for more detailed and localised assessments, including knowledge of

socio-economic factors• Actual GWIP will be greatly influenced by irrigation efficiency and crop choices• Climate change might affect GW recharge and increase crop water demand

Conclusion

References

• Altchenko Y. and Villholth K.G (2015) Mapping irrigation potential from renewable groundwater in Africa – a quantitative hydrological approach. Hydrol. Earth Syst. Sci., 19, 1-13, Doi: 10.5194/hessd-19-1-2015

• Doll P. and Fiedler K. (2008) Global-scale modeling of groundwater recharge, Hydrol. Earth Syst. Sci. 12, 863–885 pp

• MacDonald A, Bonsor H, Dochartaigh B, Taylor R (2012) Quantitative maps of groundwater resources in Africa. Environ. Res. Lett. 7, doi:10.1088/1748-9326/7/2/024009

• Pavelic P., Smakhtin V., Favreau G., and Villholth K.G. (2012). Water-balance approach for assessing potential for smallholder groundwater irrigation in Sub-Saharan Africa. Water SA, 38(3), 399-406. doi.org/10.4314/wsa.v38i3.18

• Siebert S., Burke J., Faures J.M., Frenken K., Hoogeveen J., Döll P., and Portmann F.T. (2010). Groundwater use for irrigation - a global inventory. Hydrol. Earth Syst. Sci. Discuss., 7, 3977–4021.

• Wada Y., Van Beek, L, Viviroli D., Dürr H., Weingartner R. and Bierkens M.: Global monthly water stress: 2. Water demand and severity of water stress, Water Resour. Res., 47, W07517, doi:10.1029/2010WR009792, 2011.

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