Practical application of climate-induced projected changes in water availability to underpin the water planning process in Victoria, Australia

Numerous climate change studies have recently, and are currently, being carried out across many regions of the world. However, is there sufficient confidence in the outputs of global climate models (GCMs) to make use of their projections at a regional scale; and secondly, if these results are to be used, how can researchers make the data directly usable by water managers? This paper shows results from a water availability study recently carried out across south-eastern Australia, and demonstrates how the results of this study were used by water resource managers in the State of Victoria in far southern south-east Australia. Across Victoria, there is a near unanimous agreement among climate model outputs of the direction of change of future rainfall, with 14 of the 15 AR4 GCMs examined projecting a reduction in rainfall across this region. Additionally, as these reductions in rainfall are quite high over the major runoff-generating areas, reductions in runoff (and therefore water availability) are also projected across the vast majority of the State. Climate change projections for this region were summarised by creating 'dry', 'wet' and 'median' future water availability scenarios for 2030 and 2060 based on results from the 2nd driest, 2nd wettest and 8th wettest (or driest) GCM. These results were then averaged across 27 catchments covering the State of Victoria so that they could easily be used by urban and rural water corporations in their future water planning. Of the 27 catchments covering Victoria, reductions in annual water availability (relative to the long term historical average) are projected for all 27 under both the 'dry' and 'median' future climate scenario for both 2030 and 2060. For the dry future scenario for 2030, projected reductions in water availability range from 18% to 34%, while for 2060, the reductions range from 34% to 58%. For the median future climate scenario, for 2030, reductions in water availability range from 8% to 22%, and 9% to 36% in 2060. Under the 'wet' future climate scenario, only 5 catchments project an increase in water availability for 2030 and 2060. These catchments are located in the far north and east of the State. The remaining 22 catchments project reductions in water availability of up to 11% by 2030 and 19% by 2060. These results have been used in defining a range of plausible water availability futures which Victorian water corporations are using in preparing updated Water Supply-Demand Strategies for all the supply systems that they manage. These strategies aim to balance supply and demand over the next 50 years. The reductions in water availability projected under the dry climate change scenario by 2060 are smaller than the reductions in water availability experienced during the recent drought (1997-2009) across much of the State. As climate research has shown that this drought appears to be at least partly linked to global warming, a future scenario based on a return to the dry conditions of the recent drought (1997-2009) in the short-term has also been included in the planning process. In those regions where there is near-unanimous agreement among GCMs as to the direction of climate change impacts on rainfall, projected changes in water availability can be used by water resource planners to assist them in better planning for future changes in supply. Even then however, climate researchers and hydrologists must work closely with water managers to ensure that the information is provided in a usable way.