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Congress: 2008
Author(s): Mkhwanazi M., Rodriguez Diaz J.A.
Dr JW Knox, Centre for Water Science, Cranfield University Mr M Mkhwanazi, Department of Water Resources, Government of Swaziland Dr JA Rodríguez Díaz, Department of Agronomy. University of Cordoba

Keyword(s): climate change; irrigation; sugarcane; Swaziland; water resources
AbstractINTRODUCTION As in other African countries, including Nigeria, South Africa, Zambia and Zimbabwe, sugarcane production in Swaziland forms the mainstay of the country’s agricultural economy. Although fertile soils and high temperatures provide ideal conditions for production, all are dependant on irrigation to supplement low rainfall during the growing season. Over 95% of water resources in Swaziland are used for irrigation. But new sugarcane developments are adding further pressure on constrained water resources. The impacts of climate change with higher temperatures and changing rainfall patterns is expected to exacerbate the situation. Climate change is thus likely to have a significant impact on sugar cane production, water resources and the country’s economy. METHODOLOGY Using selected IPCC SRES scenarios (IPCC-TGCIA, 2001), a series of climatic datasets were derived using outputs from the HadCM3 model (Gordon et al., 2000). The net annual irrigation water requirements (mm) and crop productivity (t ha-1) for sugarcane for the baseline and selected future IPCC scenario (with and without CO2-fertilisation) were then simulated using DSSAT, a crop growth model (ICASA, 2006). Using a GIS procedure developed by Rodríguez Díaz et al (2007), maps showing the predicted spatial changes in agroclimate across the country were produced. A linear correlation between agroclimate and irrigation need was then derived and used to estimate future changes in total volumetric water demand. The procedures developed are applicable in other countries where sugarcane is cultivated and where appropriate datasets are available. RESULTS AND DISCUSSION The crop modelling showed that to produce a unit weight of sucrose equivalent to current optimum levels of production, irrigation water requirements would need to increase by 20-22% under the IPCC SRES B2_2050 and A2_2050 scenario, respectively. With CO2-fertilisation, the impact of climate change on water use is offset by higher crop yields, such that irrigation needs are predicted to increase by 9% under the A2_2050 scenario. Total volumetric irrigation water demand for sugarcane production in Swaziland is predicted to increase from 10.5 x 106 m3 yr-1 to 12.4 x 106 m3 yr-1. The agroclimate maps show that potential soil moisture deficits (reflecting the changing balance between rainfall and evapotranspiration, ET) are predicted to increase significantly across the country under all scenarios with major implications for both water supply and irrigation demand. The maps highlight areas where adaptation strategies for responding to changing water demand due to climate change need to be concentrated. CONCLUSIONS The outputs from a global circulation model (GCM), a crop growth model and a GIS have been used to model and map the spatial and temporal impacts of climate change on sugar cane production in terms of crop productivity, water use (irrigation) and volumetric water demand. The implications of climate change with respect to managing water resources for sugarcane production are shown to be significant. A discussion of both the short-term coping plans and longer-term strategic adaptations required to adapt to changing water availability under increasing conditions of seasonal water scarcity are presented. The analyses have application to other African countries dependant on water resources for sugarcane production. REFERENCES Gordon, C. Cooper, C. A. Senior, H. Banks, J. M. Gregory, T. C. Johns, J. F. B. Mitchell, R A. Wood (2000). The simulation of SST, sea ice extents and ocean heat transports in a version of the Hadley Centre coupled model without flux adjustments. Climate Dynamics 16: 147-168. ICASA (2006) DSSAT Version 4. (Accessed: 11 Aug 2006). IPCC (2001) Climate Change: The Scientific Basis. Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, New York, NY, USA, and Cambridge, United Kingdom. Rodríguez Díaz, JA, Weatherhead, EK, Knox, JW, Camacho, E (2007) Climate change impacts on irrigation water requirements in the Guadalquivir river basin in Spain. Regional Environmental Change. DOI 10.1007/s10113-007-0035-3.
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