10/6/2014 EAU4Food Introduction to the hydrology of the Letaba basin, South Africa 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 11 10/6/2014 The aim of a modelling approach: try to keep it simple To give information/results for the discussion Letaba in the Limpopo basin, Southern Africa 22 10/6/2014 33 10/6/2014 Map of the Letaba basin and the major dams Water balance study using SIMGRO model Letaba River 44 10/6/2014 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 ) 55 10/6/2014 Land use data (National Land Cover 2000) calculation unit in the model – 1.5 * 1.5 km Area of smallĉholder farms Greater Giyani 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 66 10/6/2014 Gauging stations to compare measured and calculated flows Measured and calculated discharges at Engelhard Dam (in KNP) 77 10/6/2014 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 88 10/6/2014 Experimental Farms in EAU4FOOD project Experimental Farm Dzumeri (Adam) pump capacity (m 3/day) from GRIP database = borehole point data 99 10/6/2014 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 1010 10/6/2014 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 1111 10/6/2014 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 1212 10/6/2014 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 Kruger National Park 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% 1313 10/6/2014 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 1414 10/6/2014 This project is partly financed by the European Union 1515.