There have been several assessments of the implications of climate change for Kakadu National Park or elements thereof. The most substantive study to date was undertaken by Bayliss et al. (1997) which assessed the vulnerability of predicted climate change and sea level rise in the Alligator Rivers Region.
More recent assessments include the National Coastal Vulnerability Assessment Case Study of the South Alligator River Catchment (BMT WBM 2010) and the Implications of Climate Change for Australian World Heritage Properties: A Preliminary Assessment undertaken and published by the Australian National University in 2009 (ANU 2009). Climate change research relevant to the Park and wetland management has also been undertaken for some time by eriss as outlined in Bartolo et al. (2008).
Overall, the principal threats to the wetland values of the Kakadu National Park Ramsar site from climate change can be summarised as follows:
increased rate and extent of saltwater inundation into freshwater coastal environments due to sea level rise and storm surge events
response of mangrove communities to rising sea level, and
more intensive fire regimes that eventuate due to hotter dry seasons and the resulting damage these hot fires have on monsoon forest.
5.3.1Saltwater Intrusion into Freshwater Areas
A range of studies have been conducted to predict the impacts of sea level rise on saltwater intrusion processes with claims of a 50 percent loss of Kakadu National Park’s freshwater floodplain wetlands based on a one to two degrees Celsius increase and a complete loss of wetlands from a two to three degree Celsius increase (Hare in Bartolo et al. 2008). Bayliss et al. (1997) indicated that all wetland areas in the region below four metres in elevation are assessed as being vulnerable to climate-induced changes.
A more recent and detailed study by the authors (refer BMT WBM 2010) used hydrodynamic and catchment modelling outputs to assess the increased risk of saltwater intrusion from sea level rise and extreme rainfall events on low-lying coastal wetlands in the South Alligator River catchment. The tidal channel and floodplain model indicated that the sea level rise predictions resulted in the most significant impact, as these increased water levels were efficiently propagated up the river to the tidal head (landward limit of the tidal component of the system). Storm surge impacts were less significant, both in the degree of increase and also because they are associated with cyclones which are expected to happen about once per year.
Interpretation of the tidal component results suggested increased tidal pressure on dendritic channels within the South Alligator River system. This may act to keep channels open for longer or force them to extend further. In addition, increased tidal flows and velocities are expected to occur due to an increased tidal prism. Resulting impacts may be dramatic, particularly if tide levels overtop river banks and/or levees. Significant changes may occur if a greater volume of tidal water flows onto the floodplain via the overtopped levees.
The study concluded that the combined effect of expansion of the dendritic channel system, together with increased levee overtopping is likely to result in increased saltwater intrusion during the dry season. Subsequently, there is an increased likelihood of nearby freshwater billabongs being impacted by saltwater intrusion. This response is considered more likely for areas already threatened by saltwater intrusion and areas adjacent to tidal/dendritic channels.
Based on the previous assessments, it is clear that more precise information on areas likely to be impacted will be required including detailed topographic survey data to calibrate hydrological and catchment models used to predict sea level rises. In this context, it should be noted at the time of preparation of this ECD a detailed study of saltwater intrusion associated with sea level rise and climate change had been recommended as part of the report of the House of Representative Commission of Inquiry on Climate Change and Coastal Management.
The response of macro-tidal estuaries to sea level rise is only partially understood, but it is clear that the current trend of mangrove expansion observed over the past 50 years in the Park will continue and expand under sea level rise scenarios, particularly in those marginal saltpan areas that are currently only receiving occasional tidal inflows. As outlined in Section 3.2.1 and 3.2.2, the impacts of this will be for mangroves to continue to replace salt marsh/pan and fringing Melaleuca communities, assuming that suitable habitat conditions exist (for example, bed levels are at a suitable height, creeks are adequately flushed etc.). Inversely, current mangrove communities along downstream tidal channels and in the lower reaches of the estuaries could be at risk from more permanent inundation and water logging if sea levels rise too quickly for the communities to naturally respond. This ‘drowning’ effect has not been specifically observed at broad-scales to date in the Park but is regarded as a potential threat, particularly given the more extreme sea level rise predictions that are emerging.
5.3.3Changes to Fire Regimes
It is generally accepted that increased frequencies and intensities of fire associated with higher temperatures, longer dry seasons and increased weed prevalence threaten the values of the Ramsar site (for example, refer Section 5.1). However, perceptions and opinions about over-burning in upland areas versus the lack of burning in floodplain areas continue to be areas of contention between stakeholders (D. Lindner pers. comm. 2009)
The management challenge for Kakadu National Park is to maintain a balance between providing opportunities for the appropriate use, appreciation and enjoyment of the Park by a diversity of visitors, and protecting the rights and interests of Bininj and the natural and cultural values of the Park (refer Director of National Parks 2007). Specific threats to Ramsar values from visitor and recreational activities include:
disturbance to fauna species, particularly waterbirds, at feeding and nesting sites or during breeding season
recreational boating activities that can damage foreshore flora, promote salt water intrusion through alterations to hydrology and foreshore vegetation, spread weeds and feral animals, disturb fauna and introduce a range of pollutants through boat sewage, boat wash and subsequent erosion, leaching of anti-fouling compounds, fuel spills etc. Boating activities are also a concern for Bininj as these waterways can be important hunting and fishing grounds, and the protection of ecosystems (‘caring for country’) is an important aspect of Bininj culture, and
camping and recreational fishing leading to problems associated with litter, water pollution, fire, removal and damage to native vegetation, and associated soil erosion and soil compaction.
In general, the management regime implemented by Parks Australia is such that the potential impacts from tourism and recreation activities on ecological character are considered to be a low risk.