Climate change

2016

Updated projections of climate change in Australia were released in 2015, and are explored in the Drivers and Atmosphere reports. These new projections focus on natural resource management (NRM) areas, dividing Australia into 8 regions. The rainfall and temperature projections (CSIRO 2015) can directly inform assessment of the risk to inland waters, although the potential hydrological impacts at the national or regional levels have not been assessed. Part of the Northern Australia Water Futures Assessment (NAWFA) included risks arising from climate change and development (Close et al. 2012). The NAWFA was completed before release of the new projections, and provides catchment-scale profiles on both total risk and major threats.

Until 2012, the South Eastern Australian Climate Initiative (SEACI) undertook a range of impact studies that included long-term and seasonal hydroclimate projections for south-eastern Australia—covering most of the South Australian Gulf, South East Coast (Victoria) and Murray–Darling Basin drainage divisions. At a high level, the Phase 2 SEACI findings were:

There appear to be long-term reductions occurring in cool season rainfall and streamflow across the region. Evidence indicates that these are associated with changes in the global atmospheric circulation … pushing mid-latitude storm tracks further south and leading to reduced rainfall across southern Australia ... These trends are evident in a range of observational data and can be reproduced by global climate models … The models also indicate that these trends are expected to continue.

From a water planning and management viewpoint, one implication of these findings is that the traditional ‘filling season’ for water supply systems across most of south-eastern Australia, which historically was considered to run from about May through to November, may not be as reliable in the future. Rather, replenishment of storages (and soil moisture reserves) may in future be more dependent on spring/summer rainfall events.

In terms of the sensitivity of the run-off response to rainfall and other environmental factors, research has shown that changes in rainfall are the dominant influence, with changes in temperature and carbon dioxide concentrations having only a secondary impact. (CSIRO 2012)

Given this latter point, the NRM region projections for rainfall can be used as a guide to future run-off risks. One key risk that is not addressed as rainfall decreases is passing a threshold, such as disconnection of surface-water and groundwater processes, where the response of run-off to declining rainfall may be far from linear.

The Monsoonal North climate projections cover areas of the northern part of the North East Coast (i.e. Burdekin catchment) and Tanami–Timor Sea divisions, and most of the Capricorn Coast division. Global climate models offer diverse results for the Monsoonal North cluster, with shortcomings in resolving some tropical processes. Natural climate variability will likely remain as the major driver of rainfall changes for the next few decades. By late in the century, summer rainfall changes are projected to change by between –15 to +10 per cent and –25 to +20 per cent, depending on the Representative Concentration Pathway scenario, although these have low confidence. Winter rainfall changes are less reliable, partly because winter rainfall is low. However, there is high confidence in a future increase in the intensity of extreme rainfall events, so, although there may be little change in the average water available to the environment, the risk of extreme wet periods and floods seems likely to increase. Similar projections were made for the Wet Tropics NRM cluster, which covers the eastern part of the Capricorn Coast division and the northern part of the North East Coast division, north of Mackay.

The Rangelands NRM cluster area includes the western Murray–Darling Basin, the Lake Eyre Basin, the southern Tanami–Timor Sea Coast, the North Western Plateau, most of the Pilbara–Gascoyne, the South Western Plateau and inland parts of the South Australian Gulf divisions. Winter rainfall trends in the south of the Rangelands NRM are projected to be dominated by natural variability across the next few decades, with a high confidence in longer-term rainfall declines. The direction and magnitude of annual and summer rainfall changes are less certain, whereas extreme rainfall and time spent in drought are both likely to increase. The potential risks to inland water environments include more frequent flooding and groundwater recharge events, as well as longer dry periods when groundwater resources will be of even greater ecosystem value than now. Surface streamflow is generally low for the region, and the risk of extended periods of zero flow days will also increase.

Most of the South West Coast, the near-coastal areas of the South Western Plateau and the southern parts of the South Australian Gulf divisions coincide with the Southern and South Western Flatlands NRM cluster. There is high confidence that winter, spring and annual rainfalls will decrease in these areas in both the medium (2030) and longer term, with declines of 15 per cent and possibly up to 25 per cent by 2030, and greater reductions thereafter. There is also high confidence that extreme rainfall events will intensify in the future, although the magnitude of this is unclear. Longer times of drought are also predicted that, when combined with drier and more variable conditions, point to lower overall surface-water availability, more groundwater-surface-water disconnection, and significant impacts for water quality and inland water environments.

The East Coast NRM cluster extends from near Wollongong in the south to north of Rockhampton, thereby covering the southern half of the North East Coast and most of the South East Coast (New South Wales) drainage divisions. The models show a range of rainfall outcomes, with no clear predominating effect across much of this cluster (Table WAT6). Only medium–confidence level projections are available, and they are for decreasing winter rainfall in the southern half of the cluster, south of the New South Wales border. There is also medium confidence in the projections for increases in time spent in drought during the next century, and a high level of confidence that there will be future increases in the intensity of extreme rainfall events.

Table WAT6 Projected rainfall differences, compared with 1986–2005, for 20-year periods (centred on 2030 and 2090) and 3 Representative Concentration Pathways

Season

RCP4.5 2030

(%)

RCP2.6 2090

(%)

RCP4.5 2090

(%)

RCP8.5 2090

(%)

Annual

–14 to +3

–20 to +6

–18 to +9

–25 to +14

Summer

–14 to +12

–19 to +15

–16 to +13

–21 to +26

Autumn

–21 to +15

–27 to +15

–24 to +17

–32 to +27

Winter

–23 to +8

–22 to +6

–29 to +5

–44 to +6

Spring

–20 to +12

–25 to +13

–31 to +5

–44 to +7

RCP = Representative Concentration Pathway

Note: The 10th to 90th percentile range of model results is shown. For 2030, results for all RCPs are similar, so only RCP4.5 values are shown.

Source: Climate Change in Australia, CSIRO, East Coast Cluster Regional Brochure

Projections for the remainder of the Murray–Darling Basin drainage division—not covered under the Rangelands NRM projections discussed previously—are included in the Central Slopes and Murray Basin NRM cluster results. These areas hold a mix of medium and high confidence that, by late in the century, there will be decreases in winter–spring cool-season rainfall. Warm-season and summer–autumn rainfall is not projected to change significantly. There is high confidence in projections of increased extreme rainfall intensity, coupled with medium confidence that time spent in drought will increase during the century. For highland areas, snowfall is projected with very high confidence to continue declining over time. Thus, although a detailed hydrological outlook is not available for the eastern and southern Murray—Darling Basin based on these projections, the previously mentioned high-level implications in the SEACI findings appear likely to prevail.

The Southern Slopes NRM cluster includes the Tasmania, most of the South East Coast (Victoria) and the southern areas of the South East Coast (New South Wales) drainage divisions. For these regions, the rainfall outlook is for natural variability to dominate in the early decades of the century. Later decades have high confidence in winter and spring rainfall decreases, except for Tasmania, where there is medium confidence in increases in winter rainfall. There is also high confidence in future increases in the intensity of extreme rainfall events. In Victoria, the Victorian Climate Initiative is looking in more detail at hydrological consequences of climate change, with findings to be made available in mid to late 2016.

In terms of the potential impacts of climate change on aquatic ecosystems, recent research has:

Argent RM (2016). Inland water: Climate change. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/inland-water/topic/2016/climate-change, DOI 10.4226/94/58b656cfc28d1