Climate-Crop Integrated Assessment of Mid-Century Climate Change Impacts on Sugarcane Production in South Africa.

Previous studies mostly report positive impacts of climate change on sugarcane yields in South Africa (RSA). Predictions vary considerably, however, and the limitations in methodologies and assumptions in these studies make it difficult to quantify impacts reliably at regional and industry scales.  AgMIP  (Agricultural Model Intercomparison and Improvement Project) has developed a set of consistent regional integrated climate change impact assessment protocols that can be applied to address this knowledge gap.

The objective of this study was to use the AgMIP protocols to provide a robust indication of climate change impacts on the RSA sugar industry for the period 2040-2070 under a likely emissions scenario (571 ppm atmospheric CO₂).  Daily weather records for baseline (1980-2010) and future periods were prepared for 47 homogenous climate zones (HCZs) covering the SA sugarcane-growing regions.  Future weather data were derived from five global climate  models (GCMs).  The DSSAT-Canegro model, modified with improved capability for simulating sugarcane growth under high temperatures and elevated CO₂, was used to simulate baseline and future cane and sucrose yields, using baseline crop management (but assuming no restrictions in irrigation supplies), at each HCZ.  The impact of a single crop management adaptation, whereby age at harvest was reduced at each HCZ proportionally to increases in future seasonal thermal time accumulation, was also assessed.

GCM-averaged simulated cane yields per HCZ changed by between -3.0 and +15.5%  (+7.1% on average) while sucrose yields changed by between -5.9% and +21.9% (+8.1% on average), with no adaptation.  With adaptation, future cane yields increased by 10.1% on average compared with non-adapted baseline production, although sucrose yields increased only 5.1% on average, 3.0% points lower than without adaptation.   Analysis of interactions between different cropping cycles and climate change at each HCZ points to further adaptation opportunities with mill opening and closing dates and length of milling season.  Results indicate future increases in annual sugarcane production of approximately 1.2 million tons, provided that field management quality (including current pest and disease severity levels), area under cane and irrigation supplies are maintained.