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Assessing Climate Change Impacts andRisks on Three Salt Lakes in WesternVictoria, AustraliaD. G. C. Kirono a , D. M. Kent a , R. N. Jones b & P. J. Leahy ca CSIRO Marine and Atmospheric Research, Aspendale, Victoria,Australiab Centre for Strategic Economic Studies, Victoria University,Melbourne, Victoria, Australiac Environmental Monitoring Unit, EPA Victoria, Centre forEnvironmental Sciences, Macleod, Victoria, Australia

Available online: 13 Jan 2012

To cite this article: D. G. C. Kirono, D. M. Kent, R. N. Jones & P. J. Leahy (2012): Assessing ClimateChange Impacts and Risks on Three Salt Lakes in Western Victoria, Australia, Human and EcologicalRisk Assessment: An International Journal, 18:1, 152-167

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Human and Ecological Risk Assessment, 18: 152–167, 2012Copyright C! Taylor & Francis Group, LLCISSN: 1080-7039 print / 1549-7860 onlineDOI: 10.1080/10807039.2012.632291

Assessing Climate Change Impacts and Riskson Three Salt Lakes in Western Victoria, Australia

D. G. C. Kirono,1 D. M. Kent,1 R. N. Jones,2 and P. J. Leahy3

1CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia; 2Centrefor Strategic Economic Studies, Victoria University, Melbourne, Victoria, Australia;3Environmental Monitoring Unit, EPA Victoria, Centre for EnvironmentalSciences, Macleod, Victoria, Australia

ABSTRACTSalt lakes are significant landscape features in Australia. The three studied lakes,

in particular, are recognized as being of national (Gnotuk) and international signif-icance (Keilambete, Bullenmerri) for their ecological, social, and scientific values.The lake levels have been declining since the mid-1800s, the likely cause being anatural climate-driven decrease in precipitation and increase in evaporation. Withthe prospect of human-induced climate change further altering regional climate,this article presents a framework and results for assessing the impacts and risks ofclimate change on lake levels and salinity. A lake water balance model was appliedwith the inputs of climate observations and modeled future climate variables. Thelatter are generated from 14 general circulation model simulations used in theIntergovernmental Panel on Climate Change Fourth Assessment Report. The re-sulting scenarios represent the range of likely outcomes of regional climate underenhanced greenhouse conditions to year 2100. Models project that all lake levels arelikely to continue to decline, with the declines for Bullenmerri expected to exceedthose of the other two lakes. The salinity in the lakes is likely to increase, with therate of increase likely to become more rapid over time. Some implications of thesefindings are discussed.Key Words: climate change, Australian closed lakes, salt lakes, climate change

impacts and risks.

INTRODUCTION

As the most arid continent on Earth, Australia has a large number of salinelakes and wetlands. They range from relic lakes formed under wetter climates, toephemeral, to permanent. These saline lakes are significant landscape features atboth the local and regional scale, but face many environmental problems (Timms

Address Correspondence to D. G. C. Kirono, CSIRO Marine and Atmospheric Research, Vic,Australia. Private Bag No 1, Aspendale, Victoria 3195, Australia. E-mail: dewi.kirono@csiro.au

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Climate Change Impacts on Salt Lakes in Victoria, Australia

2005). These environmental problems include surface inflow diversions, excessivegroundwater extraction, mining, pollution, biological disturbances, and climatechange. The importance of salt lakes and their environmental threats worldwide isdescribed in Williams (2002), while Timms (2005) discusses the threats to Australiansalt lakes in particular.

The three studied lakes—Lakes Gnotuk, Keilambete and Bullenmerri in WesternVictoria—are permanent saline water bodies in the well-studied Western DistrictLakes (WDL) region (Figure 1). The lakes lie about 150 km southwest of Melbourneat altitudes less than 200 m above sea level, with a temperate regional climate. Theannual mean temperature is around 13"C (ranges around 8"C in winter to 17"C insummer) and annual rainfall is around 800 mm (ranges around 115 mm in summerto 240 mm in winter). During summer, solar radiation is relatively high leadingto a high atmospheric moisture deficit, hence evaporation exceeds precipitation.Geomorphologically, these lakes are in the area of the Western Volcanic Plains ofVictoria—a broad plain of the Newer Volcanic Province of southeastern Australia(Joyce 2003). Details of the lakes’ physical characteristics can be found in Jones et al .(2001) and a summary is provided as follows: (1) Lake Keilambete is a circular lakewith an average diameter of about 1.8 km covering an area of 250 ha in a catchmentof 417 ha. Its lake level is 28.0 m and its salinity is 102.7 part per thousands oftotal dissolved solids (hereinafter referred to as ppt). Keilambete is therefore ahypersaline lake; (2) Lake Bullenmerri is a cloverleaf-shaped lake with an averagediameter of 3.2 km and covers an area of 490 ha within a catchment of 882 ha. Itslake level is 88.6 m and its salinity is 9.2 ppt (brackish); and (3) Lake Gnotuk is asmaller lake, 220 ha in area within a catchment of 722 ha. Its lake level is 39.3 m andits salinity is 58.8 ppt (hypersaline).

In the WDL region, there are nine shallow and episodically filled lakes regardedas a Ramsar site (Ramsar sites are chosen because they are wetlands of internationalimportance in terms of their ecology, botany, zoology, limnology, or hydrology (www.ramsar.org)). These lakes support large bird population and possess unique floraand fauna (Environmental Protection Authority Victoria, pers. comm., 2009). None

Figure 1. Locations of the three study lakes (circles) and the climate stations whosedata are used in the study (i.e., Terang and Camperdown [triangles]).Gnotuk is located approximately 1 km adjacent to Bullenmerri (colorfigure available online).

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D. G. C. Kirono et al.

of the three lakes in this study are listed in the Ramsar site. However, since 1997extremely low rainfall in the study region has led to the drying of many WDL (Leahyet al . 2007). Given the likely impacts of climate change on the hydrology of lakes inthe region, the absence of deeper more permanent lakes in the WDL Ramsar sitepresents a challenge for conservation in the region. Future lake level predictions mayhelp natural resource managers determine conservation priorities in the region.

Like most Australian salt lakes, the three lakes lie in endhoreic basins, that is,closed basins that retain water and have no streams coming in or out. This and otherfactors (such as a high lake/catchment area ratios and a very low groundwater in-put) mean the water levels of the lakes are predominantly controlled by rainfall andevaporation at the water’s surface. In addition, compared to other ecosystems saltlakes are very sensitive to climate change (Williams 2002; Timms 2005). Even smallchanges in the hydrological budget will quickly lead to physico-chemical and biolog-ical changes; one major reason for this phenomenon is that salinity is inversely cor-related with water level and biodiversity is inversely correlated with salinity (Williams2002; Timms 2005). Saline lakes therefore offer a unique opportunity to quantifythe effects and mechanisms of climate change (Jones et al . 2001; Williamson et al .2009). The three study lakes have been the focus of climate/hydrology (Jones et al .2001; Tibby and Tiller 2007), limnological (Timms 1976; De Deckker and Williams1988; Tibby and Tiller 2007; Leahy et al . 2001), and palaeoecological studies (Bowlerand Hamada 1971; De Deckker 1982).

Previous research has shown that the water levels of the lakes have been declin-ing since the mid-1800s, following a period of relative stability lasting most of theprevious millennium (Bowler 1981; De Deckker 1982). The decline coincides withthe first European occupation of the region in around 1840 (Kiddle 1961) andprecedes the widespread change to the landscape that followed occupation. Bowler(1970) and Sutcliffe (1968) speculated that the fall in water level was due to climatechange of natural origin. Jones et al . (2001) showed that there was no other viableexplanation. The decline in water level was initiated by a decrease in precipitation(P) and evaporation (E) ratio from a pre-1840 value of 0.94–0.96 to the recent valueof 0.79 (Jones et al . 2001). It is likely that the future human-induced climate changemay include change in regional precipitation and evaporation, which in turn mayadversely affect most of the salt lakes in the region (Williams 2002). This articletherefore presents a framework and results on assessing the impacts and risks ofhuman-induced climate change on lake levels and salinity. It also discusses someexamples which illustrate the implications of these findings.

STUDY FRAMEWORK

Most research on the hydrologic impact of climate change adopts a predictiveapproach. These studies begin by generating climate change scenarios that are thenfed into hydrologic and/or water management models to evaluate the differences insystem performances under different climate scenarios (Hostetler and Giorgi 1995;Qin and Huang 1998; Chiew et al . 2009).

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Climate Change Impacts on Salt Lakes in Victoria, Australia

Climate change scenarios are commonly developed through Global Climate Mod-els (GCMs). Currently, there is a range of available GCMs, each developed by a dif-ferent scientific group around the world. For the historical period (#1900–2000),climate simulations were conducted using observed emissions of greenhouse gasesand sulphate aerosols, while for the future period (2001–2100), the simulationswere conducted using a particular emissions scenario commissioned by the Inter-governmental Panel on Climate Change (IPCC) and reported in the Special Reporton Emissions Scenarios (SRES) (IPCC 2000). For example, the SRES-A1B depicts veryrapid economic growth, a global population that peaks in mid-century and declinesthereafter, and the rapid introduction of new and more efficient technologies, witha balance across all sources. The SRES-A2 scenario depicts a very heterogeneousworld, with self-reliance and preservation of local identities as the underlying theme.Different emission scenarios will be associated with a different range of mean globalwarming patterns.

Accordingly, the issue of climate change and its impact is beset by uncertaintiesthat need to be understood and managed. These uncertainties include:

• the magnitude of global average surface temperature increase by the year un-der consideration. This combines uncertainties in greenhouse gas emissionsand resulting concentrations in the atmosphere and the so-called climate sen-sitivity, that is, the sensitivity of the global average surface temperature toincrease in atmospheric greenhouse gas concentrations;

• the regional climate response; and• the system response (i.e., the lakes) to regional climate change.

The first two uncertainties can be included by considering the regional climateresponse from a range of climate models run using different emission scenarios. Toassess the response of the lakes, we use a lake water balance model developed byJones et al . (1998, 2001) to model past climate in these lakes. The reason for applyingthis model is because of its availability, that is, it was specifically constructed andcalibrated for each of the three study lakes. Results from Jones et al . (2001) and ourstudy have demonstrated that this model is quite robust in modeling the observedlake levels and salinity of the study lakes.

The assessment framework for climate change impacts and risks of change forthe three lake levels and salinity is presented in Figure 2. Details about the mainsteps of this framework are described as follows.

Climate Change Scenarios

The time series of monthly rainfall, air temperature, solar radiation, and specifichumidity required by the lake water balance model were obtained from the CoupledModel Intercomparison Project 3 (CMIP3) database, which represents the currentstate-of-art in climate modeling and was used for the IPCC Fourth Assessment Report(http://www-pcmdi.llnl.gov). Among the 23 GCMs for which simulation is possiblein CMIP3, there are 14 GCMs (Table 1) that can be considered as they provide thedata for all climate variables required by the Jones et al . (2001) lake model. For2001–2100, the simulations were forced by the SRES-A1B emission scenario for 11GCMs and by the SRES-A2 emission scenario for three GCMs.

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D. G. C. Kirono et al.

11 GCM runs for

SRES-A1B

3 GCMruns for

SRES-A2

•rainfall•air temperature•solar radiation

•specific humidity

Observeddata

Simple-statisticalDownscaling

14 climate change

scenarios

Lakemodelling

14estimatedlake levels

14estimated

lake salinities

Likelihood ofdecline > thresholds

Likelihood ofsalinity > thresholds

11 GCM runs for

SRES-A1B

3 GCMruns for

SRES-A2

•rainfall•air temperature•solar radiation

•specific humidity

Observeddata

Simple-statisticalDownscaling

14 climate change

scenarios

Lakemodelling

14estimatedlake levels

14estimated

lake salinities

Likelihood ofdecline > thresholds

Likelihood ofsalinity > thresholds

Figure 2. Framework for assessing the impacts and risks of climate change on lakelevels and salinities.

The performance of the GCMs over Australia has been assessed, for example,by comparing the simulated seasonal-mean temperature, rainfall, and mean sealevel pressure (Suppiah et al . 2007; Watterson 2008), and annual potential evap-otranspiration (Kirono and Kent 2011) with observations. We also compared theobserved monthly climatology and modeled climatology in the location of the lakes(Figure 3), and the results indicate that most GCMs have reasonable capability insimulating the present climate. As an illustration the average correlation coefficientbetween the modeled and observed mean values are 0.96, 0.94, 0.99, and 0.86 forair temperature, dew point temperature, solar radiation, and rainfall, respectively.Based on this result as well as those presented in previous studies, we consider all 14GCMs as suitable for the purpose of modeling future lake levels.

Table 1. List of 14 GCMs used.

Horizontal Emissionresolution scenario

GCM Modeling group, Country (km) used here

CCCMA T47 Canadian Climate Centre, Canada #250 A2CCCMA T63 Canadian Climate Centre, Canada #175 A1BCSIRO-MK3.0 CSIRO, Australia #175 A2CSIRO-MK3.5 CSIRO, Australia #175 A1BGISS-AOM NASA/Goddard Institute for Space Studies, USA #300 A1BGISS-EH NASA/Goddard Institute for Space Studies, USA #400 A1BGISS-ER NASA/Goddard Institute for Space Studies, USA #400 A1BIAP-FGOALS LASG/Institute of Atmospheric Physics, China #300 A1BINMCM Institute of Numerical Mathematics, Russia #400 A1BIPSL Institut Pierre Simon Laplace, France #275 A2MIROC-H Centre for Climate Research, Japan #100 A1BMIROC-M Centre for Climate Research, Japan #250 A1BMRI Meteorological Research Institute, Japan #250 A1BNCAR-CCSM National Center for Atmospheric Research, USA #125 A1B

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Climate Change Impacts on Salt Lakes in Victoria, Australia

Figure 3. Comparison of observed and modeled long-term climatology for climatevariables required in the lake water balance model for Terang (air tem-perature = AT, Dew point temperature = TD, solar radiation = G, andrainfall = PR). The upper and lower panels show the mean and standarddeviation, respectively (color figure available online).

Since the lake-hydrological processes occur on a finer spatial scale (<10 kms)than simulated within GCMs (#200 kms), there is a need to “downscale” the GCMdata before they can be applied for local use. A variety of approaches can be used forthis purpose such as statistical downscaling and dynamical downscaling (for a com-plete review, see Fowler et al . 2007). However, the lake water balance is dependentmainly on rainfall volume and total evaporation, which are grid scale phenomena.Therefore, a simple-statistical downscaling method was used to translate the GCMgrid scale information to the local scale. Firstly, for each GCM and each monthly cli-mate variable, the raw time series was converted into an anomaly time series, relativeto the baseline period (1881–2008 for Bullenmerri and Gnotuk, and 1887–2008 forKeilambete). Secondly, the GCM anomaly time series was scaled using the observed(historical) baseline data to create a modeled climate time series.

Homogenous baseline time series constructed by Jones et al . (2001) were ex-tended. For the historical period (#1860s to 1990), high-quality observed rainfalldatasets were constructed by Jones et al . (2001); one for Lake Keilambete (based onTerang station) and one for Lakes Gnotuk and Bullenmerri (based on Camperdownstation). Single high-quality records were prepared for temperature and sunshine

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ratio/downward short-wave radiation and a lower quality record of dewpoint tem-perature (by Jones et al . 2001). The latter does not cause a large error for themodeled lake levels and salinity (Figures 4 and 5) because it is the least sensitiveof the climate variables used. In this study, these data sets were extended to 2008based on data from Terang (for Keilambete) and Camperdown (for Gnotuk andBullenmerri) as obtained from the SILO Patched Point Dataset (Jeffrey et al . 2001).Although the SILO data are available for the 1889–2008 period, Jones’ data wereused as they have undergone rigorous quality control for application to the studyregion.

Estimating Lake Level and Salinity

The lake water balance model estimates water balance and salinity by volumetricmeans. Because the lakes are closed, they accumulate cyclic salts within the crater,becoming more saline as the water level falls. Lake evaporation and catchmentpotential evapotranspiration are calculated using the method of Morton et al . (1985)adjusted for regional radiation characteristics (Jones et al . 2001).

Lake water level is predominantly determined by rainfall and evaporation atthe lake surface, and salinity is inversely related to surface water level. Since theupper limit of salt in water is about 350 ppt and the highest value recorded inwestern Victoria is 330 ppt (Leahy et al . 2010), the models use the 330 ppt value

Figure 4. Observed (circles) and modeled annual lake level. Black line isobservation-based estimate, grey line is the multi-GCM median, whilethe grey envelope shows the 10th and 90th percentile range.

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Climate Change Impacts on Salt Lakes in Victoria, Australia

Figure 5. Observed (circles) and modeled annual salinity. Black line isobservation-based estimate, grey line is the multi-GCM median, whilethe grey envelope shows the 10th and 90th percentile range. Observeddata are obtained from Barton and Polach (1980), De Deckker andWilliams (1988), Mooney (1997), and EPA Victoria.

as the maximum value of salt in water. Lake surface evaporation is calculated byfactoring the suppression of evaporation due to the presence of dissolved salts by1% for every 10 ppt (Morton et al . 1985). The volume of groundwater flowing intothe lake is derived from springflow (baseflow) originating from a surrounding low-yield aquifer and infiltration into the water table within the topographic catchment.The baseflow sub-model assumes the ratio of potential to actual evapotranspirationdeclines linearly when soil moisture is between field capacity and wilting point(Boughton 1966) and the percolation is proportional to soil moisture storage (soiltransmissivity). Further details about the mathematical representation of the model

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can be found in Jones et al . (2001), while further information about model behaviorcan be found in Jones (1995).

Both the observed climate data and the 14 climate scenario time series were fed tothe lake water balance model. The former simulates an observation-based estimateof the lake level and salinity for the historical period, while the latter simulates lakelevel and salinity for the historical period, and potential future levels to 2100.

Likelihood of Exceedance

As mentioned previously, there are inherent uncertainties in the projections asso-ciated with the future evolution of greenhouse gas concentrations in the atmosphereand the response of the climate of a region to such an increase in greenhouse gas.In the face of this problem, quantifying the uncertainties in climate change andits downstream consequences in units of probability or likelihood will help identifyrobust adaptation strategies. In other words, rather than only describing the rangeof projected salinity and/or lake level for a given lake by a given year (e.g., it rangesfrom X to Y ppt and/or from S to Z m), we can also estimate the likelihood ofexceeding given thresholds and the subsequent effect on the physical, chemical,and/or biological condition of the lakes. The assessment endpoints and/or thresh-olds can be identified, for example, through a participatory process with relevantstakeholders (e.g., natural resources managers). Since the aim of this article is todemonstrate the overall research framework, we limit our examples to some typesand thresholds values (see results in Table 2). The need to discuss more comprehen-sive and broader biological thresholds/impacts, for example, is beyond the scopeof this article.

We firstly considered the cumulative distribution of the 14 scenarios in order toestimate the likelihood of a given outcome in the years 2030, 2050, and 2070. Wethen used the IPCC’s (2007) terminology for any likelihood of the outcome. Forexample, an outcome is virtually certain if its probability of occurrence is greaterthan 99%, and an outcome is exceptionally unlikely if its probability of occurrence issmaller than 1%.

RESULTS

Lake Levels

Ranges of estimated lake levels from the late 1880s to 2100 are shown in Figure4 along with the estimated lake levels based on observed climate data (black line).The lake model seems to be very reasonable in reproducing the observed lake levels.This is supported by the very high correlation coefficients (R) between the modeledand observed lake levels, and the very small root mean square errors (RMSE) forthe modeled values: for Bullenmerri, Gnotuk, and Keilambete the R is 0.99, 0.96,and 0.99, respectively; whereas the RMSE is 1.5, 0.9, and 0.7 m, respectively.

All the simulated results show the lake levels declining over the 20th and 21stcenturies. Although the ranges of GCM-based estimates within the 20th century canbe relatively large, particularly for Gnotuk and Keilambete, those within the 21st

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Tabl

e2.

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lihoo

dof

exce

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gdi

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entt

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#20

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century are relatively narrow, suggesting a strong agreement among the GCMs (i.e.,the climate will get warmer and lake evaporation will increase).

The rate of the declines for Bullenmerri is expected to be larger than those forthe other two lakes. This is perhaps due to the fact that, compared to Bullenmerri’s,the evaporation increase rates at Gnotuk and Keilambete are lower because of thehigher salinity level in their water. As a result, in these two lakes the lake waterlevel decline rates, caused by increase in lake evaporation, are lower than that inBullenmerri.

The median estimates from the fourteen GCMs for the lake level of Bullenmerriare 65.2, 59.9, 55.3, and 49.3 m for 2007, 2030, 2050, and 2070, respectively. ForGnotuk these are 17.1, 13.1, 8.8, and 6.7 m and for Keilambete they are 9.1, 6.1, 4.8,and 3.7 m, respectively. The median estimates of the rate of change for Keilambete is–7.8, –5.8, and –4.2 cm/year in the 30-year period centered on 2030, 2050, and 2070,respectively. For Gnotuk, these are –14.5, –15.0, –10.9 cm/year and for Bullenmerrithey are –24.2, 26.1, and 30.4 cm/year, respectively.

If a threshold of 10 cm/year decline in lake levels is considered to be a rate thatmay affect the recreational infrastructure, it is virtually certain (>99% probability)that Bullenmerri will exceed a vertical reduction of more than 10 cm/year in thefuture (Table 2). On the south beach of Bullenmerri, where the current boat rampand jetties are located, the slope is approximately 1:14. This means that for a 10 cmvertical change there will be a 1.4 m shoreline retreat. At present, Bullenmerri’s boatramp and jetties already require regular lengthening in response to declining lakelevels (Insight Leisure Planning 2009), and according to this table such a problemis likely to still occur in the future.

Salinity

The salinity outputs from the lake balance models for the three lakes are pre-sented in Figure 5. As can be seen from this figure, there are only limited observa-tion data, due to the lack of regular measurement, to compare the modeled values.Nonetheless, the lake model seems to be very reasonable in reproducing the ob-served salinity values, particularly for Keilambete and Bullenmerri. The correlationcoefficient between the modeled and observed salinity is 0.98, 0.10, and 0.97, andthe RMSE of the modeled values are 1.3, 7.5, and 8.3 ppt for Bullenmerri, Gnotuk,and Keilambete, respectively.

The likely decline in the lake levels causes the projected salinity in each of thelakes to increase in the future. It is projected that Bullenmerri may reach around20 ppt by 2100, while Keilambete and Gnotuk will reach the upper limit of saltin water of this region (i.e., 330 ppt) by the end of the 21st century. The rate ofsalinity increase is projected to become more rapid over time, particularly in LakesGnotuk and Keilambete. As they approach the saturation point of salt in watertoward the end of the 21st century, however, the rate of salinity increase in Gnotukand Keilambete is likely to be relatively small. This is due to the effect of reducedlake water evaporation rates at higher salinities.

The best estimates (i.e., median of multi-GCM estimates) for the salinity of Bul-lenmerri are 8, 10, and 12 ppt for 2030, 2050, and 2070, respectively. For Gnotukthese are 91, 137, and 233 ppt and for Keilambete they are 126, 182, and 268 ppt,

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respectively. The recent observations (shown as circles in Figure 5) for Keilambeteand Bullenmerri seem to be close to the higher end of the projected salinities,while those for Gnotuk seem to be at the lower end of the GCM-based modeledsalinities. The higher end (i.e., the 90th percentile of multi-GCM estimates) of pro-jected salinity ranges for Keilambete are 199, 262, and 316 ppt for 2030, 2050, and2070, respectively. For Bullenmerri, these are 11, 13, and 16 ppt, respectively. Thelower end (i.e., the 10th percentile of multi-GCM estimates) of projected ranges forGnotuk are 169, 217, and 295 ppt by 2030, 2050, and 2070, respectively.

DISCUSSION AND CONCLUSIONS

This article presents a framework and results for assessing the impacts of human-induced climate change on lake levels and salinity of three lakes (Keilambete, Gno-tuk, and Bullenmerri) in Western Victoria, Australia. The study uses climate changescenarios simulated from 14 out of 23 available in the CMIP3 database, and utilizesthe lake water balance model that was specifically developed and calibrated for eachof the study lakes by Jones et al . (2001). However, the overall framework can be easilyapplied or extended to any other lakes (subject to lake model availability), to anyother GCM, and/or to the same study lakes but with any other lake model.

Although Jones et al .’s (2001) model assumes that water levels in the study lakesare controlled predominantly by surface water processes, it also includes the ground-water processes in the overall model. The model assumes that the lakes are closedenvironments, and hence that they would accumulate cyclic salts within the lakes,becoming increasingly saline as lake level declines. In this regard, it is worth notingthat all the results and projections we describe here are based on the simulationsfrom 14 GCMs and on the simulation from the lake water balance model used inthis study.

The study lakes are of interest because of their national (Gnotuk) and inter-national significance (Keilambete, Bullenmerri) for their ecological, social, andscientific values. In addition, the study lakes’ levels have been declining since themid-1800s due to decreased precipitation and increased evaporation of natural cli-matic origin (Bowler 1981; De Deckker 1982; Jones et al . 1998). Jones et al . (2001)predict that these trends will continue in each of the lakes until all componentsof the lake water balance are in equilibrium with the climate, or until the climatechanges again. To maintain the pre-1840s lake levels, for example, precipitationwould have to be about 95% of lake evaporation (Jones et al . 2001). Our results(not shown here) suggest that averaged over the last hundred years or so (#1881to 2008), the P/E ratio at Keilambete, Bullenmerri, and Gnotuk was about 0.76,0.79, and 0.77, respectively. Moreover, for the last 10 years (1998–2008), these ratiosbecome 0.68, 0.67, and 0.66, respectively, causing accelerated declines in the lakelevels.

The potential evolution of lake levels modeled through to 2100 based on climatescenarios from 14 GCMs suggests that all lake levels will continue to fall, with thedeclines for Bullenmerri—Victoria’s deepest natural lake—expected to be largerthan those for the other two lakes. The median of multi-GCM simulation suggeststhat for Bullenmerri the future P/E ratio is likely to be around 0.72, 0.69, and 0.66,

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and the lake level is likely to be 65.2, 59.9, and 49.3 by the 2030s, 2050s, and 2070s,respectively.

According to the results of a likelihood of exceedance analysis presented in Table2, it is Very likely (>90% probability) for Gnotuk and is About as likely as not (33 to 66%probability) for Keilambete to exceed a lake level decline of more than 10 cm/yearby 2030. In contrast, it is Virtually certain (>99% probability) that Bullenmerri willexceed these thresholds. Therefore, the problem already faced by Lake Bullenmerri,that is, its boat ramp and jetties require regular lengthening in response to declininglake level, is likely to persist in the future.

In addition, the simulations suggest that the projected salinity in each of the lakeswill increase in the future (Figure 5). However, it is Unlikely (<33% probability) forGnotuk and About as likely as not for Keilambete to change from hypersaline tosaturated by 2070. By then it is also About as likely as not for Bullenmerri to changefrom brackish to saline.

Potential changes in salinity will in return influence the ecology of the lakes.Generally, increasing salinity is associated with decreasing lake biodiversity althoughthe relationship is not always simple since the upper limit of salt tolerance is alsoinfluenced by other environmental factors such as dissolved oxygen, the ionic com-position of the water and whether the change in salinity happens in an abrupt ora slow process (e.g., Hart et al . 1991; Williams 1998; James et al . 2003). For exam-ple, in some of the Western District Lakes (WDL) such as Lakes Modewarre, Bolac,Tooliorook, and most recently Lake Colac, thousands of fish have perished at eachlake as a result of low rainfall and rapid increases in salinity in the lakes (Leahy et al .2007).

The upper salinity threshold for fishes present in Lake Bullenmerri such asAustralian bass (Macquaria novemaculeata) is 20 ppt (Merrick and Schimda 1984),while brown trout (Salmo trutta) and rainbow trout (Salmo gairdneri) are well knownfor their ability to survive in seawater salinity of around 35 ppt (Molony 2001). InLake Bullenmerri, it is About as likely as not for the projected salinity to be 20 pptor more and it is Exceptionally unlikely (<1% probability) that this will reach 35 pptor more by the 2070s (Table 2). In this regard, brown trout and rainbow trout inBullenmerri are likely to survive in the future.

However, many factors such as pH, dissolved oxygen, and temperature are likelyto significantly reduce the tolerance of these fishes to salinity (Molony 2001). For ex-ample, thousands of dead trout were reported in Lake Bullenmerri in 2009 (Cooper2009). Even though there have been no direct studies on the environmental condi-tions causing this event, it is likely there were various contributing factors (Environ-mental Protection Authority Victoria, pers. comm. 2009), including low dissolvedoxygen, high pH, brackish salinity, and high algal concentrations. Furthermore, arecent report details that high salinity, high pH, low dissolved oxygen, and highwater temperatures were found to be contributing factors to other large fish kills inWestern Victoria between 2004 and 2006 (Leahy et al . 2007). Taking these studiesinto account, therefore, although brown trout and rainbow trout may still be ableto tolerate the salinity in the future, the combined effect of rising salinity with otherenvironmental conditions may still pose a threat to these fishes in Lake Bullenmerri.

Additionally, the potential shift in other components of the ecosystem (e.g., algaeand invertebrates) that influence the whole food web may also put this important

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recreational fishery and wetland ecology at risk. According to data in Table 2, thelikelihood of exceeding salinity thresholds of some macroinvertebrates and zoo-plankton in Bullenmerri is Exceptionally unlikely in the future. For Gnotuk, however,it is Very likely that some zooplanktons and macroinvertebrates will not survive as thesalinity exceeds their thresholds.

Table 2 is merely an example from which we can describe some implications ofthe projected changes in lake levels and salinity for the three study lakes. It doesnot contain a comprehensive list of thresholds that can demonstrate, for example,the broader biological impact. However, the scenarios’ data stemming from thisstudy will allow this Table to be extended to any risk assessment endpoints and/orthresholds, if these endpoints and/or thresholds have been identified by relevantstakeholders (e.g., policy, adaptation, and mitigation groups, and natural resourcesmanagers).

Between 1997 and 2010, many seemingly permanent lakes in Western Victoriahave dried (Leahy et al . 2010). Shallower lakes have dried more or less permanentlyand deeper lakes have receded. The loss of these lakes is likely to have led tothe loss of biodiversity, social assets, and economic input across the region. In lessthan a decade, more than 10 Western District Lakes that were used for commercialor recreational fishing no longer sustain fish (Leahy et al . 2007). In 2010, it wasreported that only three natural lakes, including Bullenmerri, are able to sustainfish (Leahy et al . 2010). Deeper lakes like those in this study, that are more resilientto climate change, will become the focus of increasing environmental, social, andeconomic importance. This suggests that a regional plan to manage the lakes inWestern Victoria under a drying climate is urgently needed.

ACKNOWLEDGMENTS

This project is funded by the Environment Protection Authority (EPA) Victoria.The authors acknowledge Dr. Penny Whetton and Dr. Ian Smith for their valu-able input during the study. The journal’s guest editors, Dr. Ramasamy Suppiah,and two anonymous reviewers are thanked for their constructive comments on theearlier draft of the article. Dr. Vanessa Kirkpatrick provided the proofreading andcopyediting for the revised version of the article.

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