2.3 Measuring the effects of climate change

Although scientists can predict the broad pressures that are likely to emerge from projected climate change, there remains uncertainty about the exact effects of climate change, particularly at small scales. The vulnerability of any particular region at any particular point in time will be influenced by the extent of exposure to changes in the climate system, the degree of sensitivity of the region to these exposures and the capacity of the region to adapt.¹²

The ACT is already seeing the effects of climate change. However, the impact of change on the population will depend on how much we can mitigate the degree of change and increase our resilience to inevitable change.

This section first looks briefly at the weather and climate experienced by the ACT during 2011–2015. It then examines the existing and likely effects of climate change on humans and the natural environment.

2.3.1 ACT weather and climate, 2011–2015

As we have noted previously, Australia’s climate is naturally variable. However, it is still useful to look at weather during the reporting period, especially in relation to the usual drivers of variability.

During 2011–2015, the weather in the ACT was generally warmer in the daytime than the long-term climatological average (1961–1990). Night-time temperatures during the four years were near average or below average. The ACT experienced some of its hottest daytime temperatures during the reporting period (Figure 2.13). In 2014, there were three days when temperatures reached at least 40 °C, equalling the 2009 record, and 19 days reached at least 35 °C – nearly four times the average of five days each year.

The graph shows that, the weather in the ACT was generally warmer for each month in 2011–2015 than for the long‑term climatological average of 1961–1990.

Figure 2.13 Comparison of monthly observed maximum ACT temperatures with the long-term average (1961–1990), July 2011 – June 2015

The ACT region, particularly during winter and spring, can be influenced by the ENSO (see ‘Climate variability’). The conditions throughout 2011 and 2012 were influenced by the 2010–2012 La Niña, which brought heavy rains and cooler temperatures to much of Australia’s south-east (Figure 2.14). A near El Niño in 2014 brought warmer temperatures to the region. Although 2013 was a neutral ENSO year, it was the second warmest year on record. January, July and September of 2013 all broke their long-term monthly records, and winter was the equal warmest on record; 2013 followed 2006 as the warmest year on record. Since 2012, rainfall has been below the long-term average in the autumn and winter months.

The graph shows that ACT rainfall has generally been below the long-term average since 2012, particularly in the autumn and winter months. It also shows that there have been occasional months with very high rainfall above the long-term average, including November and December 2011, February and March 2012, November 2013 and December 2014.

Figure 2.14 Comparison of actual monthly ACT rainfall with the long-term monthly average (1961–1990), July 2011 – June 2015

2.3.2 Impacts on humans

The ACT community faces a number of serious challenges related to climate change, including decreased rainfall, and increased temperatures and fire danger:

Water supply. It is expected that there will be reduced rainfall and run-off in the ACT, leading to reduced water in our catchments and dams. This is likely to compound the pressure on water supply from population growth. Water quality in the ACT’s lakes, dams and waterways may also decline with reduced flows and increased temperatures. Reductions in water quantity and quality typically affect human wellbeing through
- restrictions on residential and commercial water use
- health hazards associated with toxic algae outbreaks
- a decline in recreation, amenity and aesthetic values, including challenges in maintaining green space.
Human health. Climate change has both direct and indirect health impacts. The adverse health impacts of climate change will be greatest among people on lower incomes, older people and the sick. Impacts include
- an increase in heat-related illness and death. The number of heat-related illnesses and deaths in the ACT is likely to rise as a consequence of an increase in the number of very hot days above 35 °C. The number of illnesses and heat-related deaths in the ACT could more than double, with older people particularly vulnerable. Currently, an estimated 14 people aged 65 and over die each year in Canberra from heat-related deaths (1997–1999 average). This could potentially rise to 37–41 deaths each year by 2020, and 62–92 deaths each year by 2050
- a decrease in cold-related illness and death. The population of the ACT is also susceptible to cold-related deaths, with three people each year currently dying from the cold. The proportion of people dying from the cold is expected to decrease as temperatures increase; however, as population growth is also expected, the total number of cold-related deaths is projected to be between 4 and 9 deaths in 2050
- bushfire impacts. The increased incidence of bushfires also poses significant risks to human health, through death and injury, smoke pollution and negative impacts on water quality
- disease. There may also be a greater risk of vector-borne infectious diseases, as insects carrying disease find new ranges as a result of changing temperatures, including malaria, dengue fever and Ross River virus disease. There is also evidence of an expected increase in some foodborne illnesses.
Human wellbeing. Indirectly, the effects of climate change on things like the amenity value of the landscape, the ability to recreate outdoors and the number of extreme events has impacts on both physical and mental health.
Extreme events. The anticipated increase in temperatures and evaporation is likely to result in more frequent and more intense heatwaves and bushfires in the ACT, with significant economic, social and environmental consequences. An increase in fire weather will increase the chances of direct injury and death, as well as health problems associated with a decline in air quality, which is particularly significant for those with asthma and chronic lung disease. There are also significant costs associated with property damage from fire. In rural areas of the ACT, fire can result in the loss of stock and farm infrastructure.
Agriculture. The agricultural sector in the ACT and surrounding regions is particularly vulnerable to climate change impacts. Grazing, cropping, horticulture and viticulture could all be negatively affected by reduced rainfall and run-off, increased fire risk, and increased average temperatures and hot days. These pressures are likely to have an impact on the mental and physical health of farmers, as well as reducing the financial benefits to the ACT economy.²⁷

Flooding at the Googong Dam spillwayPhoto: ACT Government

2.3.3 Impacts on the natural environment

Climate change is already altering the biophysical environment – plant and animal species, and their relationships and habitats are transforming. These changes rarely result in improvement and are likely to continue.

Changes in rainfall and temperature, and increases in extreme events, are likely to affect the natural environment in and around the ACT. The function, composition and structure of both water- and land-based ecosystems are likely to be affected. The changing conditions may be favourable to the spread of weeds and pests. Species reliant on special habitat, such as the Corroboree Frog, may face extinction. The lack of connectivity of ecosystems in the ACT could limit the ability of species to adapt to the changes. An increase in the number of fire events is also likely to put further pressure on particular plants and animals.

Ecosystems

For the biophysical environment of the ACT, the following climate change impacts are likely:²⁸

changed patterns of run-off and stream flows
reduced soil moisture and nutrients
increased erosion and soil salinity
increased drought severity, and bushfire frequency and intensity.

Specific threats have also been also identified for a number of ACT ecosystems:

Alpine and subalpine ecosystems
- increased threat to cold climate–adapted and narrow temperature–range species such as those in feldmarks, short alpine herbfields, and sphagnum bogs and fens; Southern Corroboree Frog and Mountain Pygmy Possum
- increased fire risk to groundcover and fire-sensitive species such as those in sphagnum bogs and alpine herbfields; Alpine Ash and Mountain Plum Pine
- invasion of more temperature- and fire-tolerant species, including certain tree, heathland, shrubland and weed species (eg Ribbon Gum, grevillea, Wild Parsnip).
Subalpine grassy woodlands
- reduction in snow, groundcover and grasses, which will threaten some fauna (eg Broad-Toothed Rat, Alpine Skink, frogs, echidnas)
- more invasive species (eg rabbits, hares, cats) and increased grazing pressure (eg kangaroos, wallabies, horses, hares)
- changed seed germination, regeneration and recruitment periods (eg less cool time available for Alpine Ash and Snow Gum)
- earlier flowering of annuals and shrubs, which will disturb synchronicity for migratory birds (eg Flame Robin, Pink Robin)
- spring breeding season shortened (eg for Richard’s Pipit, some honeyeaters)
- increased loss of microhabitats (eg tree hollows for Yellow-Bellied Gliders, leaf litter for ground-dwelling fauna)
- increased frost heave, which may decrease organic decomposition and soil nutrients
- effects on nutrient cycling by invertebrates and soil fauna.
Tablelands – woodlands
- stresses on fragmented and less storm-buffered woodland trees (eg Box–Gum Woodland, Blakely’s Red Gum, Snow Gum), including water pests, insects and diseases, which make this community more threatened than subalpine woodlands
- increased fire frequency, which will reduce the range and abundance of some fire-sensitive species (eg Blueberry Ash)
- increased risk to fauna from further woodland habitat and microhabitat loss, reduced plant and grass growth, and reduced or changed timing of flowering, nectar, pollen, foliage or seed, including
  - nectivorous and insectivorous woodland birds (eg Hooded Robin, Diamond Firetail, Regent Honeyeater, Superb Parrot)
  - small mammals (eg possums, Sugar Glider, Squirrel Glider)
  - ground dwellers (eg antechinus, Smoky Mouse)
- increased opportunity for invasive species (eg Indian Myna, Noisy Miner)
- reduced woodland habitat available for seasonal migratory birds from subalpine regions (eg Gang-Gang Cockatoo, robins in winter) and from the north (eg Rainbow Bee-Eater, Dollarbird in spring), as well as for native refugee species from further west (eg Galah and Crested Pigeon)
- asynchrony in arrival of migratory species if responding to temperature cues
- increased impacts on already stressed grasslands through invasive species such as summer-growing C4 grasses (eg Kangaroo Grass) and weeds (eg Scotch Broom, Blackberry, Serrated Tussock, St John’s Wort, Chilean Needlegrass, African Lovegrass), replacing winter-growing native C3 grasses and tussocks (eg Poa), spring annuals and perennials
- higher carbon dioxide and some increase in growth season from higher temperatures and reduced frosts, which may promote some extra overall growth (including shrubs); reduced rain and increased grazing could potentially offset this effect
- increased impacts on threatened grassland fauna (eg Grassland Earless Dragon, Striped Legless Lizard, Golden Sun Moth) because of the decreased productivity of temperate grasslands, as well as changes in species composition and weeds. The decreased grass cover also increases susceptibility to predation by birds (eg kookaburras, Brown Falcon) and feral species (eg foxes, cats)
- extra vulnerability through reduced habitat for already stressed species (eg Spotted Tree Frog), and for autumn and winter breeders dependent on moisture (eg Common Toadlet, Bibret’s Toadlet)
- loss of damp grassland cover and habitats, which threatens fauna requiring wetter environments (eg Green Bell Frog, Golden Bell Frog).
Tablelands – dry sclerophyll forests
- dry sclerophyll forests in tableland ridge tops and hill slopes are less vulnerable than other forests or woodlands because they are less modified, but extra heat and dryness could mean lower ground-level productivity (eg grasses), and a more open structure could affect fauna (invertebrates and granivorous species) and lead to more grazing impacts
- some eucalypts may be displaced by arid-adapted acacias
- changed flowering frequency and timing, especially in eucalypts (eg White Box, Mugga Ironbark), will affect insectivorous species (eg Regent Honeyeater, Superb Parrot, mammals, bats), including those with synchronised spring breeding
- fewer resources will be available for winter-breeding fauna such as dasyurids (eg antechinus)
- more fire may not advantage shrubs because of poor soils and nutrients, but will reduce hollows (eg for bats, arboreals, birds), and log and leaf litter protection for small mammals from predators (eg cats, foxes).

Dickson urban wetlandPhoto: ACT Government

Soil

Projected climate change has the potential to have severe, but variable, impacts on soils, depending on the bioclimatic zone and the intrinsic vulnerability of the soils in that zone.²⁹^–³¹

The major impacts expected on soils in the south-eastern region as a result of projected climate change are:

a major increase in sheet, rill, gully and streambank erosion caused by increased rainfall and run-off events
exacerbation of dryland salinity – which is currently a problem in areas of the Southern Tablelands that already experience lower-than-average rainfall – caused by any modification to groundwater hydrology.

Improvements in organic matter accumulation and overall carbon levels may occur, but these may be offset by a decrease in biomass protein, leading to changed soil biodegrader activity, increased soil erosion and increased evaporation.

Changes to rainfall erosivity in summer will most severely affect many of the region’s sodic soils. The reduction in winter precipitation is likely to have severe implications for alpine areas, where alpine humus soils (Tenosols and Organosols) dominate. In addition, increased soil biodegrader activity in subalpine areas caused by increased temperatures will lead to significant loss of organic matter in areas of alpine humus soils.

Water

Projected changes to rainfall and, hence, water availability have the potential to affect both the quantity and quality of our water resources. (See Chapter 6: Water for further details.) Government and community action will be needed to protect our water resources, and the habitats and species that depend on them (see Case study 2.2).

Case study 2.2 River rehabilitation

Artificial log jams were constructed on the Cotter River as part of the Tharwa Fish Habitat Project. Photo: ACT Government

Climate change is likely to cause decreased flows in the Murrumbidgee River, which will reduce the availability of, and access to, good river habitat for fish. The Tharwa Fish Habitat Project has installed structures that will help fish survive stressful climatic conditions by increasing the depth of the river channel and providing habitat. These structures have been placed in a degraded stretch of river that is the corridor between two good river sections.

Engineered log jams near Tharwa are a rehabilitation activity undertaken as part of the Upper Murrumbidgee Demonstration Reach (UMDR) initiative. The UMDR is a 100-kilometre stretch of river from Bredbo to Casuarina Sands. The log jams, which are made of interlocking hardwood logs and rock, will benefit native aquatic species including threatened Murray Cod, Trout Cod, Macquarie Perch and Murray Crayfish. Water flowing past the log jams is scouring away a century of sand build-up from human-induced erosion, deepening the channel to help fish move between good habitat and breeding zones.

The Tharwa Fish Habitat Project has received funding of approximately $300 000 and is supported by organisations including the Australian Government, the ACT Government, ACTEW and the Southern ACT Catchment Group.

The river corridor will be further improved and stabilised with tree planting, weed control and site rehabilitation under the ACT Million Trees Program. This revegetation will improve bank stability, thus reducing the risk of erosion and further deposition of sediment into the river.

Despite the short amount of time since completion, channel deepening in the UMDR has already been observed.

Completed log jams in the Cotter River. Photo: ACT Government

2.3.4 Resilience to pressures

A resilience assessment involves looking at the systems, networks, human resources and feedback loops involved in maintaining environmental values (see Chapter 9).

It is important to understand the drivers and impacts of climate change in order to develop strategies to address the risks they pose to human wellbeing and the natural environment. Building resilience in the social and environmental systems of the ACT is a core part of these strategies, as building resilience enables a focus on maintaining the desired values of the ACT’s environment despite the effects of climate change.

Natural ecosystems have been identified as one of the sectors most vulnerable to climate change in Australia. It is therefore likely that the delivery of ecosystem services will be substantially altered under future scenarios of climate change.¹⁵^–¹⁷ To date, there have been few studies that have specifically looked at climate change impacts on ecosystem services on the Australian continent,¹⁵^,¹⁷ but research from Europe and North America has identified key effects that are likely to occur in many regions.³²^–³⁶

In the ACT region, the combined effect of decreased rainfall, increased temperatures and increased fire incidents is likely to substantially alter the function, composition and structure of ecosystems.¹⁸ Existing threats to biodiversity may be exacerbated.³²^,³⁷ As a result of these various climate change impacts, the capacity of ecosystems to provide benefits such as clean air, food and water may be hampered, and the cultural values of ecosystems may be diminished.

a As reported in Loughnan et al,²⁵ Bambrick et al²⁶ identified an upper mortality threshold of 33 °C daily maximum temperature for Canberra.