A preliminary assessment of climate change impacts on sugarcane in Swaziland

The spatial and temporal impacts of climate change on irrigation water requirements and yield for sugarcane grown in Swaziland have been assessed, by combining the outputs from a general circulation model (HadCM3), a sugarcane crop growth model and a GIS. The CANEGRO model (embedded with the DSSAT program) was used to simulate the baseline and future cane net annual irrigation water requirements (IRnet) and yield (t ha-1) using a reference site and selected emissions scenario (SRES A2 and B2) for the 2050s (including CO2-fertilisation effects). The simulated baseline yields were validated against field data from 1980-1997. An aridity index was defined and used to correlate agroclimate variability against irrigation need to estimate the baseline and future irrigation water demand (volumetric). To produce a unit weight of sucrose equivalent to current optimum levels of production, future irrigation needs were predicted to increase by 20-22%. With CO2-fertilisation, the impacts of climate change are offset by higher crop yields, such that IRnet is predicted to increase by 9%. The study showed that with climate change, the current peak capacity of existing irrigation schemes could fail to meet the predicted increases in irrigation demand in nearly 50% of years assuming unconstrained water availability.