MORE INFORMATION- CLIMATE CHANGE

Potential Impacts of Climate Change on the Central Coast of NSW

According to CSIRO modelling,  it is projected that by the year 2030,  Sydney is likely to experience from 4 to 6 days greater than 35°C compared to an annual average today of 3 days.  By 2070 the frequency of days greater than 35°C is expected to increase to between 4 to 18 days. Lower and more variable rainfall and greater surface evaporation will see more severe droughts in southern Australia, especially in the west. The CSIRO projections for changes in extreme climate indicate that south-east NSW is likely to experience an increase in annual extreme events, with increasing intensity of extreme rainfall events in summer. In the winter months there is likely to be a decrease in the number of extreme events and the intensity of rainfall concurrent with a trend towards reduced winter rainfall.

At present the modelling work is not clear as to whether increased storminess is likely to be an issue on the Central Coast in the near future.  This question is important in light of the significant extent of low-lying coastal land and of river and lake floodplain subject to human settlement and ongoing high development.

IPCC scientists estimate that the global sea level rose at a rate of 1.3 to 2.3 mm per year during the period 1961 to 2003. Similarly CSIRO modelling work and recorded tidal gauge data indicated a global average sea level rise of 1.8 mm/yr to 1.9 mm/yr (+ or - 0.2 mm) from 1950 - 2000.  This is almost a 100 mm increase in 50 years.  The IPCC models, project that sea levels will rise further, by between 18 and 59 cm up to the end of this century without even considering possible additional contributions from changes in the ice sheet  flows of between 10 to 20 cm.

Impacts on Coastal Environment

In general terms the consequences of such potential sea level rises for NSW coastal communities could include:

  • loss of sandy beaches, especially where they are backed by seawalls;
  • increased flood levels in the tidal reaches of estuaries by approximately the amount of sea level rise, this will be especially significant around coastal lakes and lagoons;
  • changed estuarine tidal regimes (flows and elevation);
  • problems with local drainage in the lower estuaries and adjacent to beaches where falls are currently small, potentially exacerbating nuisance storm flooding (increased frequency and water depths);
  • reduction in under bridge clearances;
  • landward migration of mangroves and salt marshes in areas of no development and, where development restricts migration, potential loss of threatened and endangered species.

While the uncertainty around predictions of global climate change is understood in general terms, there has up until now been a lack of precision about the extent of its consequences for the built and natural environments of coastal NSW.  In recent years, Gosford City Council has led the way in correcting this deficiency with their application of LiDAR (Light Detection And Ranging) airborne laser technology to the task of high-precision mapping of low-lying areas in the Gosford Local Government Area. Further work by the NSW Department of Planning in cooperation with other councils has led to the high-precision mapping of low lying areas in the entire Central Coast - Newcastle - Hunter region.

Figures 1 and 2 are summary maps of the land elevation data to very high resolution (i.e. 0.15 m vertical and 0.6 m horizontal) collected in the LiDAR survey within the Gosford and Wyong Local Government Areas.



Figure 1: Digital elevation model (DEM) of areas below 20m AHD for the Gosford City LGA. Main areas of low lying land (<10m AHD) occur in the shorelines adjacent to Broken Bay, around the foreshores of Brisbane Waters and within the river valleys draining to the Hawkesbury River. Blank area in Brisbane Waters is an area of no data in DEM.

(Source: NSW Government Department of Planning, ‘High resolution terrain mapping of the NSW Central and Hunter coasts for assessments of potential climate change impacts.’ http://www.planning.nsw.gov.au/plansforaction/pdf/terrainmapping_central_hunter_coasts_report.pdf p. 30 )


  
Figure 2: Digital elevation model (DEM) of the Wyong Shire LGA highlighting areas below 10 m AHD. Major areas of low lying land occur around the entrance and foreshore of Tuggerah and Budgewoi Lakes and along the main drainage lines and river deltas on their western shores.

(Source: NSW Government Department of Planning, ‘High resolution terrain mapping of the NSW Central and Hunter coasts for assessments of potential climate change impacts.’ http://www.planning.nsw.gov.au/plansforaction/pdf/terrainmapping_central_hunter_coasts_report.pdf p. 39 )

 

 

Based on this LiDAR survey work, the Department of Planning report concluded that there are at least 2000 hectares (15 %) of  land in the Gosford Local Government Area (LGA) that are less than or equal to 1 meter above present mean sea level and about 850 hectares (5 %) in Wyong. Of this land, 300 ha of wetlands (55 % of the total wetland) in Gosford are less than or equal to 1m below sea level and 200 ha (20%) in Wyong

(Source: ‘High resolution terrain mapping of the NSW Central and Hunter coasts for assessments of potential climate change impacts.’ Appendix E).

In Gosford LGA, there are 330 properties (about 1%)  less than or equal to 1 m  above sea level and 226 properties (about 0.5 %) in the Wyong LGA. Over 16 km (1%) of roads across the Central Coast and 0.5 km (1.5%) of rail line are less than or equal to l m  above sea level - all of which could be at risk over the next century from rising sea levels predicted by Climate Change models.

Financial Risks

The insurance and finance industry is one body that is particularly concerned about climate change.  In 2005 a risk assessment carried out by the NSW Department of Natural Resources conservatively estimated the value of coastal properties at risk from coastal erosion/inundation to be $1 billion over a one hundred year planning period. 

Drought and Water Security

Australia’s climate is one of the most variable in the world.  Fresh water supplies are often under stress from drought. Under the projected climate change scenarios of increasing temperatures (resulting in higher evaporation loss and reduced runoff) water supply authorities will be challenged to meet the multiple demands placed upon them by an expanding human population. In March 2007 at the most extreme point in the recent widespread drought in southern Australia, the amount of fresh water held in storage on the Central Coast of NSW dropped to as low as 13% of the total storage capacity. While it would be  rash to directly link this particular drought to global warming, what is demonstrated by these recent events is the vulnerability of our natural water supplies should climate change models prove to be correct in their projections of an increased aridity in the southern Australia. Not only the quantity of supply but also the quality of the water may be affected by increased soil erosion following drought, lower flows, and warmer temperatures, which increases the likelihood of algal blooms and eutrophication.  
Human Health

Human health is another factor that is affected by changing climate conditions.  Already around 1,100 people are estimated to die each year due to high temperatures in Australian capital cities and heat related deaths are expected to increase due to climate change. Diseases such as dengue fever could become more widespread as the geographic range of disease carrying insects is increased by climate change. Of course, climate change may also produce some benefits to health; for example, in a global warming scenario, it would be reasonable to expect a reduction in deaths from those syndromes that would normally be worsened by cold-season conditions.

Biodiversity

Many species and ecosystems will not be able to adapt to climate change. Local ecosystems threatened by climate change need to be considered not only in terms of the value of services they bring to the community, for example, clean drinking water, shade and shelter, health and lifestyle benefits, tourism but also in terms of  their intrinsic value.

Landward transgression of mangroves, displacing saltmarsh communities is already widely reported in the literature to be responsible for the losses of up to 80% of saltmarsh in the estuaries of Qld, NSW, Victoria and SA over the past five decades.
Typically, in the Tuggerah Lakes estuary, as saltmarsh vegetation attempts to migrate landward to adapt to increasing sea level it is squeezed against the footpaths and roadways at the urban interface and lost.  There has been an estimated 85% loss of saltmarsh and fringing vegetation around Tuggerah Lakes estuary over the period of urbanisation.

Fire Risk

Higher temperatures, decreased rainfall, and increased evaporation rates are likely to result in increased risk of bush fires in bushland and urban fringe areas.  Local government authorities and the Rural Fire Service have extensive databases and up to date mapping that detail the fire regimes of many bushland remnants on the Central coast.   Bushland management may need to be incorporated into a more regional approach to protect biodiversity with consideration given to the continuing functionality of wildlife corridors which contain the many floodplain vegetation communities located on the coastal plains.