technical features climate change refereed paper CLIMATE CHANGE IMPACT ON ROUS WATER SUPPLY D Kirono, G Podger, W Franklin, R Siebert Abstract Under this scheme the secure yield is defined as the annual Climate change poses significant demand that can be supplied risks to the security of water from the headworks over the resources in many parts of 103 year historic record and Australia. This study investigated the implications for which satisfies the 5/10/20 secure yields of a regional water rule, i.e.: supplier in NSW. The aim of • restrictions of any kind the study was to estimate future should not be applied for more secure yields, using the than 5% of the time (> 1862 Integrated Quantity and Quality days); Model (IQQM) and a range of • restrictions of any kind climate change scenarios, to should not be imposed more identify the most appropriate than one year in ten on average time horizon for making new (> 10 years); and investments in infrastructure. • the system should be able to The assessment concluded that, supply 80% of normal demand when taking into consideration (i.e. 20% reduction in impacts of global warming, the consumption) through a repeat need for a new source will be of the worst drought on record. most likely after 2018, Water presently comes from consequently planning needs to two main supply storages: commence in 2008. Rocky Creek Dam and Introduction Emigrant Creek Dam. The There is an increasing body of former has a storage capacity of research that supports a picture 13,956 ML and a safe yield of of a warming world with about 9,600 ML/annum (DIPNR, 2004) while the significant changes in regional Figure 1. Rous Water scheme (Rous Water, 2006). climate systems (IPCC, 2001; latter has a capacity of 820 ML IPCC, 2007). This has with a safe yield of about significant implications for the 1,100 ML/annum. There are reliability of water supplies across Australia (NSW). The third section describes the also some other small sources (Jones and Preston, 2006). It is important framework built to assess climate change under Council control with a combined to consider the risk that climate change impacts on Rous Water’s supply. Section safe yield of about 900 ML/annum. poses to catchment yield within the context four presents and discusses the assessment Based on population projections and other of changing demand. procedure and subsequent results, and considerations, GeoLINK (2005) estimated This project investigated the implications section five summarises the main that the best estimate of the likely future that climate change may have on Rous conclusions of the study. demand from the Rous Water scheme in Water’s regional water supplies. The aim of the year 2030 is around 18,000 Overview of Rous Water Regional the study was to help identify the most ML/annum. This equates to an increase of appropriate time horizon for making new Water Supply 43% over the current demand of 12,600 investments in infrastructure. Rous County is located in northeastern ML/annum. To manage this growth in The first section provides an overview of NSW and is part of the Wilsons River demand, Rous Water adopted a water Rous Water’s regional water supply scheme, catchment, from Lofts Pinnacle in the west, management strategy in 1995 that was the second discusses the projected climate along Nightcap and Koonyum ranges near amended in 2004. The strategy provides a change profile for New South Wales the coast (Figure 1). Rous Water is the range of options to meet water regional water supply authority providing requirements. One key objective of Rous The need for a new water in bulk to a number of Councils, Water’s strategy is to implement effective from Lismore to Ballina, with an demand management, the target being a source is most likely in approximate population of 93,000. The minimum 10% reduction in per capita supply system was designed based on the demand by the year 2011, relative to 2005. 2018: planning should former NSW Department of Public Works Recognising future demand may outstrip start in 2008. and Services definition of ‘secure yield’. existing sustainable yield, the strategy 68 MARCH 2007 Journal of the Australian Water Association technical features climate change refereed paper identified two additional supplies, Lismore source and Dunoon Dam. Lismore source is a medium-term solution which is able to assist in meeting the high demand projection up to 2024. It consists of a pumping station capable of abstracting up to 30 ML/day from the upper reaches of the tidal pool in the Wilsons River, which is only utilised when Rocky Creek Dam is below 95% capacity and is subject to abstraction licence constraints. The proposed Dunoon Dam is located downstream of Rocky Creek Dam and captures local inflows as well as Rocky Creek dam spills (CMPS&F, 1995). An Overview of Climate Change in NSW During the 20th century, the globally averaged surface temperature increased by 0.6 ± 0.2ºC with the warmest year being 1998, followed by 2005 (WMO, 2005). In Figure 2. Framework for climate change impact assessment for Rous Water Scheme. NSW, the temperature has also been steadily increasing over the last fifty years (BOM, 2006). In northeastern NSW, change, scientists have developed climate Framework for Impact Assessment temperatures have increased at the rate of scenarios from global climate models º Impact and risk assessment is one stage in a approximately 0.4 C per decade. The BOM (GCMs). Best estimates for globally average larger risk management framework. Ideally, (2006) has also shown that rainfall has been surface air warming are expected to range risk management involves all related declining in the non summer months at a between 1.8ºC to 4.0ºC at 2090-2099 stakeholders. The decision-making process rate of roughly -20 to -50 mm per decade. relative to 1980-1999 (IPCC, 2007). In is commonly circular to allow the In summer, the rainfall has been increasing Australia, CSIRO uses both global and performance of chosen decisions to be at a rate of approximately +10 to +20 mm regional climate models in the development reviewed and revisited as new information per decade. Lismore rainfall records show of regional climate change projections. that the annual rainfall has been decreasing According to Hennessy et al (2004), the on climate change and its impacts are slightly at a rate of -6 mm per decade from models tend to simulate decreasing annual- available. the late 1880s to present. Winter rainfall average rainfall over NSW, particularly in Most research on the hydrologic impact of has been decreasing at a rate of -5 mm per winter and spring. In autumn the direction climate change uses a predictive approach. decade, whereas the summer rainfall has of the change is uncertain, while in summer It begins with generating climate change been increasing at a rate of +1 mm per there is a tendency for increases in the scenarios. Climate information is then fed decade. However it should be noted that north-east. Annual-average potential into hydrologic models and/or water- the trends in Lismore’s rainfall are not evaporation is projected to increase across management systems to evaluate the statistically significant at a 95% confidence NSW. The largest changes are projected in differences in system performance under level. winter with the smallest changes in different climate scenarios. Adaptations can The climate system is highly complex, and summer. Compared to changes in the other then be designed to manage those changes. therefore it is inappropriate to simply areas of NSW, the projected changes in the Through consultations with stakeholders, extrapolate past trends to predict future north-east, where Rous Water is located, the assessment framework for climate conditions. To estimate future climate are relatively small. change impacts and adaptation for Rous Journal of the Australian Water Association MARCH 2007 69 technical features climate change refereed paper Water has been established and is presented scenario may be considered as a more study. In this variation the storages are in Figure 2. Details about the main steps in optimistic future. It describes a convergent configured to 55% capacity, which this framework are described as follows. world with the global population that peaks represents the capacity at which restrictions in mid-century and declines thereafter, are imposed on the system. This First step: preparing climate change rapid change in economic structures toward configuration is used to verify the 20% scenarios a service and information economy, with rule. As described previously, future climate reductions in material intensity and the To be able to assess the impacts on flow scenarios are commonly developed through introduction of clean and resource-efficient due to changes in climate the time series GCMs. Currently, there is a range of technologies (IPCC, 2001). This step inputs used in IQQM were modified. In available GCMs, each developed by a produced a total of 18 simulations for each the FX94D scenario IQQM uses a mixture different scientific group across the world. year and for every station used in the of observed and predicted flows that vary These models differ in their approaches to Wilsons River IQQM. between sites. The Sacramento rainfall simulating the climate, hence different runoff model was used to extend flows for models may project different climate Second step: estimating supply under most of the tributaries. Emigrant Creek futures, even when driven by the same climate change Dam was based on the Australian Water scenario of future emissions. The standard The climate scenarios were applied to the Balance Model (AWBM) rainfall-runoff measure to compare climate models is their Integrated Quantity Quality (IQQM) model while Rocky Creek dam was based ‘sensitivity’ defined by how much eventual hydrologic, river system simulation package on a monthly correlation with a nearby warming they project when the-pre- (Simons et al.