10/6/2014

EAU4Food

Introduction to the hydrology of the Letaba basin, with a focus on smallĈholder farming Erik Querner

Contents • Introduction • Modelling the Letaba basin • Scenario analysis: increased crop prod. • Focus on the 4 experimental farms – groundwater extractions for irrigation • Expected climate change • Conclusions

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The aim of a modelling approach: try to keep it simple To give information/results for the discussion

Letaba in the basin, Southern Africa

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Map of the Letaba basin and the major dams

Water balance study using SIMGRO model

Letaba River

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Some input data of the model

Rivers and streams dams

Sub basins info Land-use

Ground level data

Representative summer and winter crops (maize and vegetables) Soil map and groundwater data Drinking water abstractions Irrigation from ground and surface water Rainfall and evapotranspiration

Boreholes in urban areas ( red ) boreholes for agricultural water use ( green )

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Land use data (National Land Cover 2000)

calculation unit in the model – 1.5 * 1.5 km

Area of smallĉholder farms

Greater municipality: around 900 agricultural smallĉholder farms data Prov. of Limpopo, Dep. of Agric., Mopani Distr.

Estimated for Letaba basin: Around 7500 ha of agricultural land are smallĉholders, crop farming based on the number of boreholes

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Gauging stations to compare measured and calculated flows

Measured and calculated discharges at Engelhard Dam (in KNP)

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Scenario analysis for the Letaba basin

What is the effect of changes on river flows ?

Present situation 1. Increase production (more water applied by smallĉholders) Maximum water crop yield 2. Optimal nutrients applied – Environmental crop yield 3. Optimal water and nutrients applied – Maximum crop yield

• The change in river flows is small • Enlarging the irrigated area has a pronounced effect • Changing crops has not such a great effect

Scenarios ĉ irrigation water use Smallĉholder farms ĉ 7500 ha: all farms Present situation 450 mm/a* 33 mln m 3 1. Max. water crop yield 550 mm/a 41 2. Environmental crop yield 600 mm/a 45 3. Maximum crop yield 700 mm/a 53

* precipitation = 400 mm; irrigation from groundwater and surface water

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Experimental Farms in EAU4FOOD project

Experimental Farm Dzumeri (Adam)

pump capacity (m 3/day) from GRIP database = borehole point data

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4 experimental Farms

Groundwater extractions for irrigation

pump of 40 m 3/d 40 / 30 = 1.3 m drawdown 150 m 3/d 150 / 30 = 5.0 m ,, Horizontal groundwater flow rate (=transmissivity) – 30 m 2/d

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Zone of influence

Zone Two pumps can influence Pumping rate each other, thus a larger draw 50 m 3/d 150 m 3/d down Zone 400 m 650 m summer 800 m 1400 m winter

Overĉabstraction of groundwater?

Do not abstract more than the groundwater recharge

Groundwater indicator = groundwater recharge / g.w. extraction

see next slide

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Groundwater recharge divided by groundwater extractions

Overĉabstraction

Climate change: period 2000 ĉ 2050 grid 50 x 50 km Measured precipitation average per year: Precipitation Pot. ref. evapotr. Stat no. (mm) (mm) B8E008 291 1219 B7E004 464 1203 B8E009 798 1281 A9E002 935 1125 B7E006 966 1266 B8E003 1136 1132 B8E001 1272 1002 B8E004 1437 1064 2001 ĉ 2010 Precipitation B8E005 1443 1084 (min) (max) Summer 573 610 Winter 120 150 Total 693 760 mm/year

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Climate data CSIR (Research Organisation South Africa)

Difference in climate data between period: 2001ĉ2010 and 2041 ĉ 2050

Precipitation Temperature Potential evapotr. summer winter 2001ĉ2010 100% 100% 100% 100%

2041ĉ2050 91% 107% 90% 109% less rain warmer colder more water is needed

Climate 2050 – river flows

Modelled 2001ĉ2010 and 2041 – 2050

Its the change in river flow in the

Model results for period 2041 ĉ 2050

Change Jan ĉ Mar Apr ĉ Jun Jul ĉ Sep Oct ĉ Dec All year

river flow 68% 73% 80% 70% 69%

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Climate 2050 – groundwater levels at Mzilele farm: 0.4 – 0.8 m

Conclusions:

1. Water resources in the Letaba basin are limited

2. Increased production for smallĉholders has little effect on the water resources (river flows)

3. Climate change (2050) has an enormous effect on the water resources

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This project is partly financed by the European Union

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