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There has been relative stability in climate and sea level over the last 6,000 years (Holocene period) resulting in global coasts that have been, in many places, in a state of dynamic equilibrium. Early humans faced severe climatic variation and conditions, but this period of relatively mild and stable climate and sea level has allowed the significant development of the human species. Around the world, many people live and work around the coast, and large parts of the coast have been significantly altered with substantial amounts of financial investment. It is now widely accepted within the scientific community that global climate change is occurring and that over the last 100 years there have been a number of measurable changes to the climate of the planet Earth. These changes will affect coastal areas and consequently coastal communities in the next few decades (IPCC 2001). More information on the implications and evidence of climate change relating to Tasmania is provided in Enhanced Greenhouse Effect. The Case Study on Measuring sea-level rise at Port Arthur describes what is regarded as among the earliest benchmarks in the world against which to scientifically measure changes in sea-level. Climate change and the coast Some of the predicted changes to climate with respect to the coastal environment are a rising sea level and a change in the frequency and severity of coastal storms (for more information, see Global Sea Level Rise). The IPCC, an association of leading climate, atmospheric and oceanographic scientists from around the world, has released a series of sea-level rise projections as a result of climate change (IPCC Summary for policymakers). To account for various scenarios in regard to the release of Greenhouse Gases, the IPCC provides estimates for low-, medium-, and high- sea-level rise scenarios, ranging from 0.09m to 0.88m by the year 2100 on a global scale (IPCC 2001). For southeastern Australia, sea-level rise projections undertaken by CSIRO are similar to those made by the IPCC (McInnes et al. 1998) Taking Tasmania as an example, broad scale climate modelling suggests that we will face a number of climatic changes, some of which will be gradual but others will be sudden and extensive following major events such as storms. These include: Higher sea levels predicted are related to thermal expansion of oceans as temperatures in the atmosphere increase. The influence of thermal expansion is shown in the images from NASA's Jason oceanography satellite, taken during a 10-day collection cycle ending December 2, 2002. The Sea Height Image shows the Pacific dominated by two significant areas of higher-than-normal sea level (warmer ocean temperatures). While these sea heights relate to current weather, particularly El NiÑo/La NiÑa patterns, it highlights the influence of thermal expansion on oceans. However, it is the frequency and severity of storm events combined with higher general sea levels that are viewed with most concern by coastal researchers. There is evidence around the world and in Tasmania too, that these trends in sea-level change can already be identified. According to a study entitled 'Vulnerability of the Coastal Zone to Climate Change in Tasmania' (DELM and DEST 1996) data from the Hobart Station indicates a trend of increasing sea level averaging 1.41 mm per year over the last 25 years. This compares to an overall mean trend across Australia of 0.70 mm per year. There are other reasons for relative sea level change such as situations where the earth's crust is rising or falling in relative terms, however there are no significant examples of such movement in Tasmania.
Hazard: short- and long-term effects The increase in sea-level has short-, medium- and long-term effects that may act individually or in combination. These are: In general, low-lying coastal environments with 'soft' or sandy shorelines are considered to be areas most susceptible. These environments are prone not only to inundation (permanent flooding), but also to shoreline recession (erosion). Rocky shores on the other hand are considered relatively safe from the impacts of sea-level rise and coastal storms due to their more erosion-resistant composition (Davis 1986). It is important to differentiate between short-term effects (which can last for hours, days or weeks), such as flooding and short-term erosion due to coastal storms, and long-term effects (decades to centuries) such as rising sea-level, inundation, progressive shoreline recession, rising groundwater tables and saltwater intrusion. Again, low-lying sandy or muddy shorelines are likely to be most affected. In contrast to the short-term effects of storm events are long-term effects, such as rising sea-level. Rates of sea-level rise per year are typically very small for a single year (in the order of 0.2-1.0cm/year), however, the long-term effects of sea-level rise may be different, considering the possibility of a 0.88m rise in sea-level by the year 2100. The potential increase in frequency and magnitude of storm events could have devastating effects on coastal areas. The cumulative impact of a series of close-coupled storms can be far worse than that of a major storm of short duration as the recovery time for the beach is not sufficient to re-distribute the sediment back to the beach and therefore it is more vulnerable to the following storm event (Smith 1994). A higher water level caused by rising sea-level will ultimately lead to an increase in the overall water depth in the nearshore zone. This increase in water depth allows higher waves to penetrate further towards the shore, especially during storm events. As a result higher wave energies are able to impact the coast, particularly soft, sandy coastlines. The implications of this are that a storm event-currently defined as a '20-year storm event'-may, in combination with rising sea-levels, cause impacts similar to those that a 50-year storm event would have at present. This means that sea levels rise not only inundates a certain proportion of the land due to the vertical rise of the water level, it also forces the shoreline to move further inland (horizontal recession) due to the impacts of higher waves. There are two ways of estimating coastal erosion in assessing the effects of rising sea-level and coastal storms on coastal environments and communities. These are: The most widely used model for simulating the behaviour of sandy coastlines is the Bruun Model (Bruun 1962, Bruun 1988) which essentially assumes that a vertical rise in sea level by 10cm will cause the shoreline to erode horizontally by 500-1000cm (i.e., a factor of 50-100 times the amount of sea-level rise). This assumption is generalised and varies between different beaches. It is widely accepted by coastal geomorphologists as well as engineers that this approach is suitable for a first assessment of the potential sea-level rise impacts in the absence of high-resolution, long-term data. Risk - what are the potential consequences for coastal communities? Worldwide, an increase in the popularity of coastal areas and beachfront properties can be observed, often called the 'rush to the shore' (Pilkey et al. 1989). This situation is clearly reflected in Tasmania, where approximately 77% or 355,247 people (ABS, 1996 of the total population are living in coastal local government areas (compared with just over 50% for Australia). Beachside residential sites are currently in high demand, and these are the locations most at risk from future sandy shoreline recession and inundation. Tasmania's coastline (including the Bass Strait Islands) is approximately 6,500 km long at 1:25,000 scale (and therefore longer than the combined coastlines of Victoria and New South Wales). This total coastline length comprises: What do those conditions outlined above mean for Tasmania and the population located in coastal areas as well as socio-economic impacts for these areas? The change in coastal population (coastal LGAs) can be seen by comparing the recent Census data (ABS). This analysis will be undertaken as part of the ongoing program for improving the coverage of this SoE Report. The additional pressure on coastal areas due to an increase in housing will exacerbate the effects of sea-level rise as an increased number of people will be affected by a rise in water level. In the past ten years houses have been built within 100 m of the shoreline, and a proportion of these are located on erodible shorelines. These houses are potentially vulnerable to coastal changes over the next 50-100 years. Any additional development close to the shoreline creates a potential legacy for future planning and management of coastal areas. The socio-economic impacts of sea-level rise are anticipated to affect a large proportion of the Tasmanian population. Even though only a small number of residents and business people will be affected directly by the impacts of sea-level rise due to direct property loss at present, future development along the coast and the implications of rising sea level and coastal storms on the wider community will be extensive. The range of potential impacts of climate change on the coast of Tasmania include: Other consequences include: These changes will affect existing infrastructure on the coast in Tasmania. In other parts of the World, enormous amounts of money are expended annually on beach protection and coastal engineering to protect infrastructure and development. In some countries already facing the effects of increased severity of storms, increased erosion, and loss of assets, communities expect their government to substantially assist in protecting their investment and in compensating them or adjusting for their losses. In these countries, and there are lessons for Tasmania, the existing risk of severe economic and social consequences will be increased by further coastal development which occurs in those areas which are at significant risk from future climate change impacts. Local and regional scale assessments of coastal vulnerability around Tasmania's coastline includes the following considerations: Assessing and measuring the current situation Work is being carried out by the State Emergency Service, in association with Councils, to identify emergency risk management requirements caused by current natural and other hazards. It is intended that this will be used to assist in the development of emergency management planning. In addition, where risks are identified as being unacceptable, cost-effective risk reduction measures will be identified and recommended for implementation. Although this work is not in a position to adequately deal with climate change impacts, as the regional information is not yet available, it does provide a risk-based model for dealing with vulnerability from climate change. The CSIRO, Antarctic Division and the University of Tasmania have a number of researchers who are seeking to understand the coastal and climatic processes that currently operate in Tasmania. This information can be used to more accurately project the impacts and identify vulnerable areas within Tasmania Improvements in digital mapping data will improve capability to identify vulnerable areas at risk from the effects of climate change around the State. Some of the essential data that are available include elevation through the digital elevation model (a core dataset of The LIST) and coastal geomorphology. Research has been proposed (subject to funding), which will help monitor the physical changes to Tasmania's coastline, in order that these can be compared with the expected changes resulting from the proposed climate change model for Tasmania. At this time, the funding is not available to carry out either of this necessary research. In Queensland and New South Wales, for example, erosion of soft shorelines is threatening considerable amounts of current investment. Research has been undertaken into the historic changes of coastline in those areas that contain considerable urban development. This research enables the pattern of coastal erosion to be identified, and also provides a baseline to monitor future changes with a high degree of accuracy. It has also revealed the extent of impact of some major storm events. These studies will assist in projecting the location, rate and extent of future erosion and the risk to existing and future development. Processes have been developed to map contours of risk of erosion and then link them to development controls. These maps clearly identify, to current and future landowners, the level of risk to their investment, development, or infrastructure. They will also assist government in selecting adaptation strategies for local areas, and prioritising major investments in beach protection and other measures. Some crude data indicates that in Tasmania, the land within 100m of the high water mark contains a considerable amount of investment. Land which is on a softer coastline and within 100m is at a higher risk of inundation or erosion over the next 100 years. More detailed work is necessary to accurately identify those areas that are vulnerable to impacts. Data are available on extreme weather events-and the extent and impacts of resultant storm surges-on coastal flooding and erosion. This historic information can then be compared to current weather records and then used to predict likely effects of future climate change. |
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Sea-Level Change - at a glance
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In broad terms, there are four main adaptation strategies that are internationally accepted as options to reduce the consequences of coastal vulnerability to climate change. In outline these are to: Abandon Abandon means to allow natural processes to continue without being controlled in any fashion. Examples include: not protecting the land and removing or demolishing any structures as they become affected by coastal processes and preventing further development in vulnerable areas. Protect Protect means to protect the area from relevant climate change impacts such as flood, storm, erosion, and inundation. Examples include the construction of flood and sea walls, beach replenishment, offshore breakwaters, and groynes. Adapt Adapt means putting in place measures that allow continued or extended use of land potentially affected by climate change. Examples may include: Retreat Retreat (or phased retreat) means putting in place measures that minimise the costs of changing the use of land as it becomes more threatened by climate change impacts. Examples may include: Selecting adaptation strategies There are a number of methods of selecting the most appropriate adaptation options for any particular vulnerable area. However, one justifiable approach is to develop risk management plans for vulnerable areas, which can then be used to select the most appropriate adaptation strategy for the local area, within a regional context. The development of risk management plans will enable avoidance of unnecessary risk by: All these adaptation strategies have different costs and impacts borne by different sections of government and the community. It is important that the necessary information is available to the community and government to allow informed decisions to be made. It is likely that the financial and social consequences of climate change impacts will be greatest in those areas that have been substantially developed. It is unlikely that Tasmania will be able to afford to sustainably provide complete protection for all vulnerable areas currently developed on the coast. It will need to make decisions on which areas it will protect, and those it will allow to be eroded or inundated, with loss of associated private, commercial and public investment. Informing and preparing the community for this eventuality will reduce false expectations in the future. Additionally, if undeveloped or minimally developed vulnerable areas are allowed to be further developed without careful planning, then these people and their investment will be placed in the line of harm. Losses will occur, demands for unaffordable protection will be made, and compensation sought. These are consequences that can be minimised by appropriate risk management measures implemented now. Decisions are being made that determine change of land use and investment in areas that are vulnerable to the impacts of climate change. It is important that policies are developed to ensure that decisions are well-informed in order to minimise avoidable consequences of climate change on the Tasmanian coast. Factors to be taken into account in designing a management response Trying to protect sandy coastal environments from sea-level rise is very expensive, prone to failure if not done to the highest standards and often causes erosion problems elsewhere if not developed as part of an integrated regional works strategy. The USA Federal Government has recently issued a paper evaluating erosion hazards on the USA coast (Federal Emergency Management Agency 2000). It states that over the next 60 years, one in four current houses within 150m of the coast will be lost to erosion. The paper goes on to say that these effects are likely to be more significant as the calculations do not include the effects of climate change or the current rapid intensification of development in these vulnerable areas. The Federal Emergency Management Agency (FEMA) conducted a program to map significant areas of erosion hazard and then identify the structures at risk within those areas. This information was used for an impact analysis of the effects on coastal communities. Tasmania needs to carry out similar research. The FEMA identified that the average USA rate of erosion is currently between 0.6m and 1.8m per year, but that a major storm can erode 30m or more in a single day. The Duke University's Program for the Study of Developed Shorelines collated data on USA beach nourishment. It identified that the USA has spent USA$3.6 billion on beach replenishment since 1923. In some cases up to a third of the replenished material is reported to have been washed away days after being placed in position. The cost in the USA of artificial beach nourishment is estimated at around US$10,000 per beach front property but this may be limited by the availability of sand in the future (Walsh, K., et al. in prep. 2002). The cost of sea wall construction was estimated at around US$3,000 per metre plus 4-10% maintenance costs per annum, dependent on the severity of wave action. Tasmania cannot afford the widespread use of such protection measures and needs to identify adaptation strategies that are more relevant to our needs and resources. The USA has experienced an increased frequency of major storms hitting its coastline. The result has been that the normal cycle of erosion and subsequent replenishment has not been completed before the next storm strikes. Subsequent storms extend the erosion further inland than previously experienced. This also provides an indication of some of the effects that Tasmania may experience. In the USA it is reported that a major insurance company had been so financially affected by the costs of several major storms in a single State that it decided that it would withdraw insurance cover at renewal. The director of general insurance development at CGNU (largest UK insurance company) reported to the international climate change conference in the Hague (November 2000) that the value of property damage from major storms is rising at around 10% per year. He expected the rate to accelerate rapidly when climate change impacts become more significant. He predicted that the insurance industry was in danger of running out of money unless it changed its risk. An insurer could change their risk by refusing to insure risks such as coastal erosion and inundation. This exposes a greater number of people to being uninsured. Other alternatives include government based insurance policies funded out of general revenue or local rates as used in the USA and UK for flooding. Increased risk for insurance companies may lead to further stringencies in their interpretations of policy cover, and ramifications for councils and other planning authorities in Tasmania may follow. Insurance companies may refuse to cover councils for claims where it could be argued that the Council did not act in a reasonable manner to avoid a foreseeable risk and failed to carry out the necessary risk reduction measures through its development control processes. It is important that policies are developed and decisions are well-informed in order to minimise avoidable consequences of climate change on the Tasmanian coast. The Premier's Local Government Council is considering a project to develop and implement an adaptation strategy to assist local government in meeting its responsibilities. In addition the State will be reviewing the Tasmania Greenhouse Strategy as part of the current review of the National Greenhouse Strategy. This will include a significant component relating to the need for a Tasmanian Adaptation Strategy. Natural Resource Management (NRM) in Tasmania is undergoing major change. There is the potential that Regional NRM Committees will be one method of providing necessary funding to carry out some of the work necessary to produce regional vulnerability mapping and adaptation strategies. Some of the other actions that could be taken to improve capacity by the community generally to better respond to coastal vulnerability issues, include: Tasmania Together and the RMPS Relevant Tasmania Together goals and standards for 'Coastal, Estuarine and Marine' are listed in the linked file. The Tasmania Together Progress Board reported on progress toward targets for benchmarks set (Tasmania Together Progress Board 2003). Indicators, targets and baseline data are available in the latest Progress Report June 2003. Further information, including progress report updates, is available from Tasmania Together. Involvement of the community, and the fair and orderly use of resources are also fundamental principles of the RMPS. The RMPS objectives have been developed to advance the principles of sustainable development.
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