In the CRPA led and DAFF funded Preparing Farmers in the Coal Valley for Climate Change the following report was a key primary outcome: Climate Change projections for the Coal River Catchment, Tasmania; Coal River Catchment Climate Change and Hydrological Modelling, Prof Roger Stone, Mr Torben Marcussen and Dr Shahbaz Mushtaq, Australian Centre for Sustainable Catchments, University of Southern Queensland, 12 September 2010.
The Executive Summary of this report is highlighted below.
“This project has selected a subset of recognised, more suitable general circulation models (GCMs) for use in regional studies of climate change for the Coal River Valley region and associated catchment. Additionally, downscaled output from the CSIRO Conformal Cubic Atmospheric Model (CCAM) has been utilised in order to dynamically downscale the results of these (five) defined, more regionally relevant, general circulation models and also following Climate Futures Tasmania’s recent report (CFT, 2009). ‘Raw output’ from the models suggested in the Climate Futures Tasmania report provided a useful data set that could be applied for precipitation, temperature, and hydrological analyses. However, complementary model analyses and associated output, applying a number of additional models and approaches, has also been set up for any ongoing or follow-up needs from this report.
Temperature projections from all five ‘more suitable’ GCM models utilised and analysed suggest an increase in regional maximum and, especially minimum temperatures, for this catchment over the scenario periods. Outputs from the models selected are generally consistent in suggesting mean maximum temperature over the region is likely to increase by 4% to 6% (1.0oC – 1.2°C) by 2010-2030 (A2 emission scenario). The lower emission scenario, B1 emission scenario, also shows an increase in the maximum temperature, albeit less pronounced compared to the A2 emission scenario. Minimum temperatures are projected to increase by 13% to 16% on a yearly basis and, notably, between 29% and 49% during winter.
Although five, more suitable, climate change models were selected (as per CFT, 2009) due to their capability in reproducing known climate drivers and known local rainfall variability, considerable variations in projected seasonal and monthly rainfall have been identified under the A2 Emission Scenario. Therefore, these model outputs are presented with required caveats. An appraisal of these model outputs of projected rainfall, suggest potential for an increase in rainfall through January-March-April for this region but, conversely, for a potential likely decrease in precipitation for this region for the May-through-November period when the overall outputs are considered.
The combined impacts of increasing temperature, potential increases in evapotranspiration, and possible reduction in winter rainfall may impose a strain on already stretched water resources in the Coal River catchment during that period. Streamflow projections using the approach presented here suggests enhanced summer (January-March) flow but reduced winter (July to September) flow with implications for water storage management and value to growers and producers.
The reduction in rainfall in late autumn through to early summer together with projected increase in minimum temperature has implications for cropping systems in Coal River Catchment, particularly for horticultural crops, but possibly with windows of opportunities for summer cropping systems.”
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