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Overview
Expected impacts for the environment
Australian ecosystems and water flows
Overview
Most Australian ecosystems are already under enormous stress from impinging and over development, along with having to absorb various forms of waste produced by an industralised nation. Whilst it has become increasingly apparent that human needs and quality of life intimately depend upon healthy ecosystems, competition for water between various users has commonly placed ecosystem needs last. From this position, many Australian ecosystems are particularly vulnerable to the impacts predicted under human-induced climate change. From expected changes in rainfall, the most vulnerable environments will include: alpine regions, rainforests, the southwest of Western Australia, and coral reefs (Pittock 2003).
Overall, climate change will have a negative affect on biodiversity, as it will exacerbate existing stresses on ecosystems, as well as creating new ones (CSIRO 2003). Therefore, with increasing human demands for water it is paramount that environmental needs are adequately represented and catered for in management decisions.
Expected impacts for the environment
FLOODS AND EROSION
With more extreme rainfall events predicted for many parts of Australia, associated flooding will occur more frequently. In such cases, more extensive flooding will affect environments sensitive to water intrusion, resulting in greater occurrences of erosion, from the loss of soil.
DROUGHTS
An increase in the occurrence and severity of drought events is expected across eastern and southern Australia, with the most severe events occurring in northeastern and southeastern Australia. Drought periods will put enormous stress upon the survival of flora and fauna with high water needs. Wetland ecosystems and temperate rainforests are particularly vulnerable. Trends in increased drought are already being experienced in southern parts of Australia, whereby the 2002 drought was recognised as being the most severe drought since 1950 (Karoly et al 2003). The 2002 drought is the first drought in Australia where the impact of human-induced climate change can be clearly observed (Karoly et al 2003).
EUTROPHICATION
Climate change is likely to exacerbate eutrophication (nutrient loading), which will result in more nutrients and chemicals being washed into streams (AGO 2002). Regions experiencing reduced stream flows and/or extreme rainfall events will be most vulnerable (AGO 2002).
SALINITY
The impacts of climate change on salinity are uncertain, however, areas experiencing reduced precipitation levels will be most vulnerable (AGO 2002). For these reasons, the southwest of Western Australia and parts of South Australia constitute the regions most at risk to salinity under climate change (Pittock 2003).
INCREASED CHANCE OF BUSHFIRE
With the combination of higher maximum temperatures and evaporations rates, along with possible reductions in annual rainfall, many southern forests and woodlands will be more prone to bushfire danger than in previously experienced (Karoly et al 2003).
LANDSLIDES
Areas that are predicted to receive increased extreme rainfall events are more at risk to experiencing landslides (CSIRO 2002).
Australian ecosystems and water flows under climate change
FORESTS AND WOODLANDS
Being partically sensitive to changes in rainfall, climate change will lead to subsequent changes in Australia's forest and woodlands (Pittock 2003). Drier fauna habitats and montane cloud forests found in parts of Queensland and Norfolk Island will be particularly at risk (Pittock 2003).
Already under stress from animal production, introduced species and human activity, rangelands will be increasingly more vulnerable to land degradation, salinisation and decrease food production under expected climate change scenarios (Pittock 2003). Specifically, heavy rainfall events will cause greater water runoffs, increasing erosion and dryland salinity in sensitive areas (Pittock 2003). Furthermore, changes in rainfall patterns will stimulate shifts in vegetation composition, spurring the growth of woody vegetation in some areas (Pittock 2003).
ALPINE SYSTEMS
Alpine ecosystems are extremely vulnerable to future climate changes. This is due to the small areas that they cover, high degree of sensitivity, seasonal snow cover and depth, and high diversity of flora and fauna, of which many are already threatened (Pittock 2003). By 2030 it is predicted that Alpine regions will experience an 18-66% reduction in snow cover, and a 39-96% reduction by 2070. Such outcomes will have a seriously adverse impact on Alpine regions, and will greatly increase the risk of fire in sensitive areas previously devoid of fire (Pittock 2003). Overall, with decreased snow and rainfall and increased temperatures, there will be little opportunity for Alpine ecosystems to adapt to climate changes.
WETLANDS
Already under threat by large developments, including dams, weirs, and channelisation, many wetland ecosystems will be pushed to their threshold under future climate changes (Pittock 2003). Depending on the severity of climate change, many species dependent on wetland ecosystems will become extinct (Hassell and Associates 1998).
The types of impacts that wetlands will be subjected to include: higher water losses from declined rainfall, changes in soil and bank erosion rates from extreme rainfall events, and some will become more saline due to sea level rise (Pittock 2003). With decreases in rainfall and stream flows, inland wetlands will have increasing competition for water with the high demands of irrigation practices. In the Macquarie Marshes alone, it is predicted that both semi-permanent and ephemeral wetland vegetation will be reduced by 20-40% of their original areas by 2030 (Hassall and Associates 1998).
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| Image: CCSA/Catherine Way |
RIVERINE ENVIRONMENTS
Many riverine environments are substantially degraded from water diversions into dams, barrages and channels largely for irrigation purposes (Pittock 2003). The National Land and Water Audit (2002) highlighted that out of 14,000 reaches of the more intensively used catchments: over 80% are affected by disturbance, 33% are classified as substantially modified, one third have impaired aquatic biota, and 90% have higher nutrient and suspended sediment loads then would naturally occur. The types of impacts that can be expected under future climate change include:
- many rivers in southeastern Australia will experience reduced stream flows, with increase intensity and frequency of drought conditions, having serious implications for the maintenance of riverine ecosystems;
- increased occurrence of both floods and droughts will disrupt nutrient levels, creating unfavourable conditions for species;
- general reductions in catchments sizes from reduced rainfall, combine with the above impacts, will exacerbate a loss in biodiversity of fish species (Pittock 2003).
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