Kakadu “underwater” in less than a century, report finds

Northern Australia’s iconic Kakadu National Park could be largely overwhelmed by rising seawater in fewer than 90 years, according to a report published this week by the CSIRO journal Marine and Freshwater Research.

The World Heritage-listed region, already besieged by invasive species such as feral pigs and aquatic weeds, could be devastated by rising sea levels in as early 2100, according to the Australian-led study. 

The report singles out Kakadu for the richness of its coastal floodplains and freshwater wetlands, which it says are highly vulnerable to future sea-level rise and saltwater inundation and storm surges caused by climate change. 

It adds that related factors, such as changes in seasonal rainfalls and predicted increases in ambient temperatures, will also affect the floodplain wetlands.

Kakadu National Park is home to 10,000 species of insects, more than 280 bird species (a third of Australia’s total), 117 reptile species, 60 types of mammals, 53 types of freshwater fish, and more than 1700 different species of plants. Many of these are rare, endangered or endemic.

UNESCO notes it is the largest national park in Australia. “Kakadu preserves the greatest variety of ecosystems on the Australian continent including extensive areas of savanna woodlands, open forest, floodplains, mangroves, tidal mudflats, coastal areas and monsoon forests. The park also has a huge diversity of flora and is one of the least impacted areas of the northern part of the Australian continent.”

The report’s lead author, Peter Bayliss, from the CSIRO’s oceans and atmosphere business unit, says researchers modelled the loss of freshwater floodplains in the Kakadu region for the present day, 2070, and 2100, with 2013 as the baseline. They determined that 60% and 78% of its freshwater floodplains will be subjected to sea-level rise and saltwater inundation by 2070 and 2100 respectively. They predicted that by 2132 all current freshwater floodplains in the region will be subjected to salt-water inundation at a mean sea level of 2.15 metres. 

However, they also believe that some upper reaches of freshwater tidally influenced river-floodplain systems will be unaffected by future sea-level rises, and these will play a key role in maintaining freshwater biodiversity by potentially “seeding” new evolving wetlands in the upper catchments. 

The report says sea levels “are predicted to keep rising even if climate change is stabilised, and will continue to do so for many centuries because of the long time-scales of the oceans and ice sheets”. For this reason, Bayliss says, “the upper 2100 limit of our projections is arbitrary”.

However, he notes 87 years is significant “with respect to planning frameworks that usually only go out to five to 10 years”. 

Such modelling is important, he adds, because the location of freshwater refuges and the most likely areas where new freshwater ecosystems may evolve will become critical.

The report says climate change “threatens the resilience of human communities that rely on ecosystems for their well-being”, adding that  coastal communities in northern Australia are particularly vulnerable to rising sea levels because they will combine with existing threats to natural and cultural values, such as invasive species, which are global challenges in themselves. 

The report’s “over-riding ‘big-picture’ conclusion” is that Kakadu by 2100 and beyond will essentially become a “no-analogue” environment, a novel ecosystem that will “render traditional management restoration and intervention goals unachievable. The present-day socio-ecological context by 2100 and beyond in the Kakadu region will be completely different.”

The region is facing “a diabolical problem that requires complex and possibly counter-intuitive solutions”, it concludes.

Bayliss says the integrated risk assessment included in the report allows managers and policy makers “to essentially travel in time to 2070 and 2100” to re-assess their strategies for combating invasive species, or any threat, while highlighting the importance of maintaining freshwater refuges in good condition now and well into the future, even if they will eventually be lost to saltwater inundation. 

“Time-travel out to long time frames may also facilitate better planning in a social context,” he adds. For example, it could allow people to adapt to rising sea levels by seeking new opportunities, such as exploring ways of preventing saltwater intrusion, or creating new freshwater ecosystems.

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