Climate Change, Adaptation Options & Prospects For The Australian Coast
Story by Professor Andrew Short
COASTALWATCH | Environmental News
The shift in climate belts as a result of global warming is likely to mean changes in wave energy and direction. There has been a detectable increase in windiness and an increase in wave height of around 0.5 cm per year observed in the region. It is less clear how the incidence of storms will change in future; although frequency may decrease slightly, increased sea surface temperatures mean that the number of very intense storms seems likely to increase. The greater intensity of storms, particularly tropical cyclones, means that storm surges will lead to greater inundation. When combined with sea-level rise this is likely to result in considerably more frequent inundation of some low-lying areas, threatening the rapidly expanding coastal communities particularly in the Cairns and southeast Queensland regions, as discussed above. These will be further threatened by alterations to runoff in the catchment, which in the case of tropical storms mean that coastal flooding is exacerbated through the coincidence of flooding watercourses with elevated storm surge water level at the coast.
SEE ALSO: Impacts Of Coastal Erosion In Australia
International concern about climate change is increasingly focused on efforts to halt the warming trend (climate change mitigation) by reducing the rate of greenhouse gas emissions and ultimately stabilising the concentration of carbon dioxide in the atmosphere. However, it will take much longer to reduce the rate of sea-level rise, because carbon dioxide is incorporated into the oceans from the atmosphere through ocean circulation that occurs over centuries.
Even if greenhouse gas concentrations can be stabilised in the 21st century, sea-level rise will continue because of the lag. If warming eventually leads to the melting of most of the Greenland ice, and significant marginal melt of Antarctica, then a rise of several metres is possible, as is considered to have occurred during the Last Interglacial, 120 000 years ago.
Meanwhile, the impacts of climate change will be felt on the coast and it is important to consider adaptation measures.
The adaptation options are:
- To protect the shoreline, e.g. using coastal defences such as sea walls or repeated renourishment of beaches with sand;
- To accommodate, for example by raising the floor levels of buildings, or
- To retreat, abandoning the shoreline to the waves. Quite sophisticated plans for progressive response have been adopted in parts of Europe, including managed re-alignment where staged inundation of the sea into formerly reclaimed wetlands will be allowed to happen. In Australia, many areas of the coast may be exposed to impacts. Although more than half the coast is composed of soft sediments (sand or mud), and hence at risk of erosion under future sea-level rise, much is remote and undeveloped and would not justify protection.
WHAT IT WILL LOOK LIKE
The energetic beaches on the wave-dominated coasts of eastern Australia are subject to substantial storm cut when a large storm occurs. In the future, it will not be the subtle and gradual upward creep of sea level that causes the greatest concern, but the impact of an extreme event, such as a major storm, where accompanying surge reaches unprecedented elevations, accentuated by sea-level rise.
The 1974 storms, for example, resulted in retreat of the shoreline by several tens of metres, and took a decade or more for the shore to fully recover. This storm cut and recovery involves large sand volumes that will mask the retreat that can be anticipated as a response to gradual sea-level rise alone. Beach replenishment and the stabilisation of dunes with vegetation are among a series of potential adaptation strategies that may need to become more widely adopted in the Australian context (as it is in Europe and North America) in those situations where the natural behaviour of a shorleline becomes unacceptable. Particularly at risk are heavily capitalised shorelines, such as the Gold Coast and the Adelaide metropolitan beaches, where such practices are already incorporated into the management of the shoreline, at great expense. Even highly developed beaches such as Bondi and Surfers Paradise could retard the impact of sea-level rise by decades using massive beach sand nourishment.
Climate change will result in further stresses on coasts already impacted by the consequences of coastal development. There can be little doubt that much of tropical Australia will experience ferocious cyclones in the future, and there will be much debate about whether or not individual storms were more intense as a consequence of human-induced climate change, as has occurred following the tragic devastation caused in 2005 across New Orleans by Hurricane Katrina.
Building codes and the lowest elevation at which buildings are permitted need to be increased appropriately in those places at risk. Ecosystems show considerable resilience in the face of the natural processes, including extreme events, but adaptation involves maximising this resilience. The reduction of non-climate stresses on coasts can also serve to increase the resilience of coasts and reduce the impacts of climate change.
For example, in the case of coral reefs, reducing the effects of overfishing and pollution, and other stresses such as sediment runoff, mean that some of the impacts associated with climate change may be less severe.
Prospects For The Australian Coast
In this story, we have traced the interaction of humans with the Australian coast. Australia was originally colonised by people whose origins remain beyond the Dreamtime. Early European explorers made contact with the coast and coastal aborigines and islanders, however their impact was transitory and their accounts were largely descriptive.
Following the arrival of the First Fleet, coastal settlements expanded and more detailed coastal survey, mapping and charting was undertaken particularly to make shipping safer and to support a maritime tradition on which Australia became dependent. Early contact between settlements relied on ships, and transport and communication was by sea. Although the 'outback' was gradually explored and settled to a limited degree, the coast has remained the focus of Australian trade and life.
Most of the population lives along the coast; the coast is where many Australians focus their recreational activities and it is the focus of most domestic tourism and the majority of international tourism.
What future faces the Australian coast? The pressures are twofold - human and natural, the latter also linked to climate change. The former can be managed and controlled to the degree that society demands. With sea change sweeping the coast there will be growing pressure for increased coastal development and density.
If we use Table 9.2 as a guide only 16% of the coast has been 'developed', while a further 12% is reasonably accessible, the vast majority (72%) is inaccessible to the average person and largely undeveloped, outside of agricultural activities.
If we then look at Table 9.3 the news is still good, with 27% of the coast already contained in national parks and state reserves, much of this located in the more populated southeastern states, while another 18% is aboriginal land, largely in northern Australia. When other crown land is considered approximately 50% of the coast is already quarantined for preservation of the natural coastal environment and ecosystems, while marine reserves, presently occupying over 600 000 km2, including 7% of Australia's vast maritime jurisdiction, and all are increasing in extent. What this means is we will see continuing growth of existing coastal centres right around the coast, but if managed properly not a lot in between, with large sections of coastal national parks and reserves and adjacent marine reserves and MPA's.
The second challenge is natural, and particularly the challenge of climate change and its associated impacts on the coast which is predicted to include sea level rise, increased tropical cyclone intensity and changing wave, wind and rainfall patterns.
Sea levels rise will result in gradual retreat and erosion of the 50% of the coast composed of sandy beaches. As Table 9.2 indicates 84% of the beaches are undeveloped and will be left to natural changes. There will only be a demand to preserve and protect the more popular 400-500 beaches at best. This can take the form of beach sand nourishment, particularly along the southeast coast where huge sand reserves like just off the coast, and as a last resort, seawalls and other structures.
The backing dune systems will be potentially reactivated by shoreline erosion however, these can be managed with dune fencing and planting. The 40% of the coast that is rocky and generally of high relief will be left to cope without interference, other than managing human use of these locations, which will become increasingly hazardous as sea level rises. The estuaries and associated wetlands will bear the largest impact, as even slight rises in sea level will produce considerable physical and ecological impacts.
The 5000km of open coast tidal flats, plus the even greater extent of low-lying estuarine salt marshes, mangroves and sea grass meadows will be gradually inundated, which will result in a landward shift where possible, of these systems. However, most of the tidal flats have taken thousands of years to evolve, and so in low energy and estuarine environments there will be a turning back of the clock to former deeper more open water conditions and in many areas a shrinking of the inter-tidally dependent salt marshes and mangroves. Likewise, the coral reefs systems that ring northern Australia will have to catch up with rising sea level or be left behind.
As climate changes the Australian and the world's coast faces an interesting and uncertain future, fortuitously in Australia with a large largely undeveloped coast, nature will accommodate and respond to the changes as it has in the past. We will soften the impact with beach nourishment along our popular beaches, build seawall, dykes and barrages to protect important infrastructure and property, and elevate our existing ports and coastal airports out of the reach of the sea.
The Challenges We Face
The present challenge is how to achieve these coastal planning and management goals while an increasing number of Australians want to live and play at the coast, and national and international tourists want to be accommodated as close to the shore as possible.
To effectively manage this demand coastal managers require detailed high-resolution environmental information, in order to access the vulnerability of the coastal zone and its ecosystems to both human pressure and natural hazards. Based on this information we then require coastal policies that are effectively managed and enforced, ensuring that the coast and its habitats are protected, that development is excluded from coastal hazard zones and sensitive and valuable coastal environments and ecosystems; and most importantly that coastal development is contained and constrained, focusing new development in existing coastal settlements, so as to avoid ribbon or strip development. At the same time large sections of coast and adjoining coastal waters need to be preserved in coastal national and marine parks, together with a representative network of MPA's. The policies also need to be cognisant of the potential impacts of climate change, so that coastal habitats have room to move, and human occupation is not put at risk.
The above challenges are well within the reach of Australian society. We already have a Commonwealth coastal policy, as well as state coastal agencies, policies and management plans. The Australian coast is in good hands and Australians are widely regarded as world leaders in coastal science and coastal management. However, we do have a massive coastline and one that is highly variable and in many areas extremely valuable, and one that is under growing pressure from society, recurring natural hazards and increased future threats. Its effective management requires a thorough understanding of how its physical and biological systems operate, based on detailed scientific studies.
The results of these can be used to underpin effective coastal management plans. The challenge ahead is for Australia to continue scientific investigation of our coastal systems, to effectively review and fine-tune the coastal policy and management plans, and to ensure the policies are enforced so that future generations may enjoy the benefits of the coast. For the first time in history we have the opportunity and ability to leave the coastal zone in a better condition than we found it.
Written by two of Australia’s leading coastal experts, Andrew Short and Colin Woodroffe, The Coast of Australia provides the first comprehensive account of the Australian coast.
Covering 36,000 km of shoreline, from iconic beaches such as Bondi and long unbroken sands of the Coorong to the endless curtain of the Nullarbor cliffs along the Great Australian Bight, this illuminating book explores these magni? cent landforms, revealing how they formed and continue to change. It details the various coastal systems that operate, including beaches, dunes, estuaries, deltas, rocky coast and coral reefs.
Based on the latest scientific investigations and thinking, The Coast of Australia will leave you with a clear understanding of the coastline, including its geological background and evolution, and the processes and ecosystems that operate around the coast.
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