Abstract
Climate is a key driver of sugarcane production and all its by-products. Consequently, it is important to understand how climate change will influence sugarcane crop productivity. Ensembles from a crop model and climate projections form part of the dual ensemble methodology to assess climate change impacts on sugarcane productivity for three major sugarcane-growing regions in Australia—Burdekin, Mackay and New South Wales (NSW). Different parameterisations of a crop model injected with climate outputs from eleven statistically downscaled general circulation models (GCM) were used to estimate regionally averaged sugarcane yields for the base period 1971 to 2000. The forward stagewise algorithm selected crop model parameterisations that best explained the observed yields. Leave-one-out cross validation assessed the predictive capability of the equally weighted crop ensemble members characterised by the selected crop model parameterizations. A Monte Carlo permutation testing procedure was employed to measure the significance of the predictive correlations. The predictive correlations between historical yields and simulated historical yields for the Burdekin, Mackay and NSW were 0.69 (p = 0.030), 0.83 (p < 0.001) and 0.70 (p = 0.034), respectively. Simulations were run based on GCM projections for 2046 to 2065 for a low (B1) and a high (A2) emission scenario, with and without elevated CO2 levels. We found it was plausible for industry to consider an increase in yields to all three regions under the B1 scenario and highly plausible for NSW under the A2 scenario. Higher CO2 levels resulted in lower demand of water for the crop, particularly in the Burdekin region and suggested that industry could expand into regions currently considered as marginal owing to the benefits of increased transpiration efficiency that are associated with increased CO2. Although this study favoured neutral or positive impacts on sugarcane production, industry should not overlook negative impacts when developing a risk management framework in response to a changing climate.
Highlights
Sugarcane industries worldwide make a valuable contribution to sustainable development
Ensemble members for the Mackay and Burdekin regions preferred a late harvest start date, while models in the New South Wales (NSW) region used a mix of harvest start dates
When rainfall was averaged across the pixels selected in the crop ensemble (Figure 2) we found projected increases in mean annual rainfall were just as likely as projected decreases in mean annual rainfall for the B1 scenario in all three regions, but increases were more likely for the Burdekin and Mackay for the A2 scenario (Figure 3)
Summary
Sugarcane industries worldwide make a valuable contribution to sustainable development. A number of climate change impact studies have been conducted for sugarcane production systems around the world. Most studies use the DSSAT-Canegro [6] or the APSIM [7] cropping systems simulators. The DSSAT-Canegro model has been used by Marin et al, [9] with three harvest dates to project São Paulo stalk fresh matter yields for 2050. Another study found yields to increase in Australia (Ayr), Brazil (Piracicaba) and South Africa (La Mercy) by 4%, 9% and 20%, respectively when they used outputs from GCMs and an elevated CO2 concentration of 734 ppm [10]
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