The big wet

By Joey Clarke, Senior Science Communicator

A dramatic wet season leaves its mark across northern Australia
Last wet season, it rained so much at Piccaninny Plains Wildlife Sanctuary that even the frogs moved inside, taking refuge in the managers’ house and croaking from the bathroom. Living on-site in some of the most remote parts of the country, Australian Wildlife Conservancy’s northern field teams are well-accustomed to the isolation and inconvenience of the annual wet season. However, this past summer saw extraordinary rainfall totals, causing disruption on a scale not seen before. In a dramatic turnaround from dry conditions and low or ‘failed’ wet seasons in 2018-19 and 2019-20, the past three years under consecutive La Niña weather patterns have been accompanied by a series of supercharged rainfall events. The AWC team in the Kimberley was affected by the most intense flooding ever recorded on the Martuwarra-Fitzroy River, while the Gulf of Carpentaria and Cape York Peninsula were drenched through February and March. The impacts of this big wet season, both positive and negative, are still being felt across the north.

Sally Gray/AWC

Triple-dip La Niña
One major contributor to recent weather was the unusual line-up of three successive La Niña events from late 2020 to early 2023. This global weather pattern is triggered by warm water currents in the Pacific Ocean and has a powerful influence over seasonal weather across all continents. In Australia, La Niña typically brings high rainfall along the eastern seaboard and across the north. This was the first instance of three La Niñas in a row this century. In March, the Bureau of Meteorology called an end to the succession of La Niñas and predicted a possible reversal to drier El Niño conditions ahead.

Kenrick Ebsary, pilot with HeliSpirit

Kimberley flood disaster
It was a disastrous start to 2023 in the Kimberley. In the days after Christmas, ex-Tropical Cyclone Ellie set a slow and meandering course from the Top End towards the north of Western Australia. By New Year’s Eve the system was hovering over the Martuwarra-Fitzroy River catchment, dumping huge amounts of rain before it moved slowly west. An automated rain gauge at Dimond Gorge registered a phenomenal 831 mm over the seven-day period up to January 3, which is 96% of the average annual rainfall for Mornington. With the ground already soaked and creeks gushing, water soon started to back up in the Martuwarra-Fitzroy River, where the narrow constriction at Dimond Gorge acted like a natural dam. Low-lying areas in the south of Mornington were quickly inundated, the Fitzroy Bluff becoming an inland island, while AWC staff and researchers at the operations base watched as Annie Creek turned into a moving mass of water and the Adcock River broke its banks, backfilling into the operations base along Home Range. Meanwhile, the Screwdriver Home Creek was also rising at Charnley River-Artesian Range Wildlife Sanctuary operations base, and the power system went down shortly after.

By Tuesday January 3 the AWC team had shifted into emergency response: with support from our partners at Kimberley Air Services, three staff members were evacuated by helicopter from AWC’s Charnley River operations base, followed by the evacuation of all eight people (four AWC staff and four Monash University researchers) from Mornington on January 4. Further downstream, the flood reached levels over 15 metres at Fitzroy Crossing, destroying bridges and displacing hundreds of people, rendering whole areas unliveable. The impact on communities in the Fitzroy River valley is substantial and ongoing.

Joshua Guthrie/AWC

A week later, floodwater had receded from both of AWC’s Kimberley operations bases. A team of AWC staff was able to fly into Charnley River and Mornington by helicopter from Derby to conduct a damage assessment. Thankfully, Charnley River sustained minimal damage, but at Mornington it was a different story. Many of the buildings had been inundated up to 1-2 metres, leaving the contents of the research offices and staff accommodation muddy and jumbled. In the steamy conditions, mould was adding to the destruction. The loss of the AWC Kimberley Herbarium – a reference collection of carefully-preserved plant specimens compiled over two decades by passionate ecologists, botanists and volunteers – was a particularly sad one.

A long path to recovery
While structurally sound for the most part, the buildings that make up the Mornington research centre, operations base and staff housing will need to be gutted and renovated. Much of this work relies on road access being re-established (still an unknown at time of writing). Heavy demand for helicopters in the region and limited stocks of aviation fuel on-site is another constraint to contend with.

Despite this big disruption, to the extent that we can, AWC is determined to continue our important conservation work in the Kimberley. Our award-winning, large-scale prescribed burning program (Ecofire) is already getting underway, being delivered alongside our partners from Wilinggin Aboriginal Corporation and Dambimangari Aboriginal Corporation.

The land management and science programs that we have developed over the past two decades at Mornington have brought about significant improvements in landscape ecological health. It will take some time to get back to normal, but we remain determined to continue this critical work, alongside our partners.

Sally Gray/AWC

Biggest wet season ever on Cape York Peninsula
On the other side of northern Australia, Cape York Peninsula was in the firing line for a series of low-pressure systems which swept across from the Gulf of Carpentaria in February and March. AWC’s Piccaninny Plains Wildlife Sanctuary received its highest wet season rainfall on record, with 2,137.5 mm falling between December 1 2022 and February 28 2023. This was the highest rainfall recorded anywhere on the Cape.

For sanctuary managers Graham Wood and Sally Gray, being isolated for a few months in the wet season is par for the course, with access by air often the only option during the wet. The sustained rainfall over this past wet season saturated the land to such an extent that even light aircrafts could not land on the airstrip, with helicopters providing the only way of getting on or off the sanctuary.

Piccaninny Plains is adorned with a remarkable network of wetlands which extend along the Archer River floodplain. The transformation from a parched, crispy, brown landscape in the late dry season to lush, vivid greens in the wet is dramatic; Brolgas and Magpie Geese flock to these areas in huge numbers, along with ducks, herons, darters, and cormorants. Across the wider plains, the team has observed a flush of growth in native grasses, which in time will provide a boon for seed-eating birds and native rodents. In the months ahead, that flush of vegetation growth will cure, creating the dry grass which fuels the yearly pattern of dry season fires, including the prescribed burns implemented annually by AWC.

Northern Australia’s 2022-23 wet season saw extraordinary rainfall and flooding from the Kimberley to Cape York. As the climate continues to shift, these record-breaking events are projected to happen more frequently. The disruption to AWC infrastructure and work programs was substantial, but we are committed to rebuilding and future-proofing our remote operations bases as best we can. The tropical ecosystems we work in show a remarkable level of resilience to disturbances; but even for plants and animals which have evolved in northern Australia’s climate of extremes, there are limits.

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