The Murrumbidgee River’s wet season height has dropped by 30% since the 1990s — and the outlook is bleak


Murrumbidgee River, near Yass.
Nick Pitsas, CSIRO/Wikimedia Commons, CC BY-SA

Milton Speer, University of Technology Sydney and Lance M Leslie, University of Technology SydneyThe Murray-Darling Basin is Australia’s biggest agricultural region, producing almost 40% of the national food supply during the growing season from April to September. It’s filled with criss-crossing rivers, wetlands and lakes farmers rely on for crops, and it’s home to a range of freshwater wildlife, many of which are under threat.

But our new research found climate change since the 1990s has drastically reduced the amount of water available in the southern part of the basin.

The height of the Murrumbidgee River — the third longest in Australia and highly valued for irrigation and hydro-electricity — has dropped by about 30% during the growing season. This is a loss of approximately 300 million litres per day that would normally flow past Wagga Wagga, New South Wales — the same as six days of water use in the City of Melbourne.

The findings follow a major report the Intergovernmental Panel on Climate Change released on Monday, which found much of Australia will become more arid as the world warms. This will bring reduced river flows, mass tree deaths, more droughts and drier soils.

The viability of the basin is at stake. Continued drying and warming in Australia will cause water availability to decline even further, deepening the hurt for communities, businesses, animals and the environment. Any decisions about the competing interests of agriculture and the environment must keep these global warming impacts front of mind.

What we found

The southern Murray-Darling Basin occupies the southern half of NSW and northern Victoria. It receives most of its water from rain in the cooler months that fills dams, with any overflow spilling into the floodplains.

But our research shows rainfall in April to May has significantly decreased which, in turn, has caused the net inflows to the Murrumbidgee River catchment in the southern basin to decrease. This includes in the main dams of Burrinjuck and Blowering in the upper part of the catchment, and downstream river heights.

Murrumbidgee River catchment makes up 8% of the Murray-Darling Basin.
Conquimbo/Wikimedia Commons, CC BY-SA

The Murrumbidgee River catchment is approximately 84,000 square kilometres, or about 8% of the basin. It encompasses a complex series of wetlands and floodplains, and supplies water for homes in many communities, including Wagga Wagga, Griffith and Leeton.

Using statistical analysis and machine learning, we found the Murrumbidgee River dropped from 3.5 metres in 1990 to 2.5 metres in 2019 during the cooler months. When you multiply this by the the length and breadth of the river, which stretches more than 1,400km, this is an enormous volume of water lost.

Given this drop is associated with the wettest months from April to September, the outlook for the warmer months between October and March is dismal. The number of days when the river ceases to flow will certainly increase.

Long, difficult droughts

Dam building and excessive irrigation are often behind decreased river flows across the Murray-Darling Basin. But in this case, we can point to decreased rainfall from climate change as the reason the Murrumbidgee River catchment is losing water.




Read more:
We looked at 35 years of rainfall and learnt how droughts start in the Murray-Darling Basin


The Burrinjuck Dam was completed in 1928 and the Blowering Dam was completed in the 1960s. Until the early 1990s, the Murrumbidgee River used to regularly spill over the banks at Wagga Wagga and also further downstream at Hay, during the cool seasons.

Likewise, we didn’t identify irrigation as a major contributor, because more than 80% of irrigation occurs downstream of Wagga Wagga.

The Murrumbidgee River is over 1,400 kilometres long, and flows past Wagga Wagga.
Shutterstock

Global warming has accelerated in the latter half of last century, and particularly since the 1990s in Australia.

To see its effect in Australia, we need only look to the extended drought conditions since the mid-1990s in the basin, comprising the Millennium Drought (1997-2009) and the 2017-2019 drought. They were extreme, even compared to the historical Federation Drought between 1895 and 1903.

In 2006, the Australian newspaper reported that inflows to the nearby River Murray system between June and November were 610 gigalitres, “just 56 percent of the previously recorded low in 1902” when the Federation Drought was at its worst.

Climate change exacerbates dry years

But climate change doesn’t tell the whole story, there are also other factors at play driving the low rainfall trend in the basin. Namely, natural climate phenomena form over the ocean and bring wetter or drier weather to various parts of Australia.

One of these climate phenomena is the Indian Ocean Dipole (IOD), which brings wetter weather than normal from June to October when in its “negative” phase (in fact, the Bureau of Meteorology recently declared another negative IOD for Australia this year, the first in five years).




Read more:
A wet winter, a soggy spring: what is the negative Indian Ocean Dipole, and why is it so important?


But in the last two decades there have been only two strongly negative-phase Indian Ocean Dipole (IOD) events affecting Australia. The current IOD phase is only moderately negative.

Climate drivers like this are entirely natural and have been occurring for thousands of years, but human-caused climate change exacerbates their influence. Generally, it makes dry seasons drier, and wet seasons wetter.

After years of little rain or snowmelt, evaporation accentuates the lack off run-off.
Shutterstock

In April this year, devastating floods engulfed western Sydney. This resulted in the dams reaching nearly 100% capacity last month. However, the river height at Wagga Wagga is currently around 5.3m and this is still 2m below the minor flood level of 7.3m — too low to overflow into the surrounding floodplain.

And after years of little rain or snowmelt, evaporation accentuates the lack off run-off into dams and streams, because water needs to soak into dry catchments before significant run-off can occur.

Profoundly disturbing implications

The implications of our research are profoundly disturbing, because it means the economic, social and ecological sustainability of the Murrumbidgee River catchment is at stake.

Under climate change, we can expect further drying of wetlands and major losses of wildlife habitat. For example, the mid-Murrumbidgee and the Lowbidgee wetlands are listed as nationally significant, providing critical habitat for threatened frogs, such as the vulnerable southern bell frog.

The southern bell frog is threatened by habitat loss and degradation, barriers to movement, predation, disease and exposure to biocides.
Shutterstock

For farmers and communities, we can expect huge reductions in the amount of water allocated for irrigation. The ability for communities to survive these severe decreases in agricultural productivity will be tested.

The efficiency of farm practices is improving. But because of the continuing threat of drought conditions in a warming climate, there’s an urgent need to plan for further decreases in rainfall, and further unreliability of water supply.

Australia needs a new review of water availability and sustainability in the Murrumbidgee and other river systems in the southern Murray-Darling Basin.




Read more:
Climate change has already hit Australia. Unless we act now, a hotter, drier and more dangerous future awaits, IPCC warns


The Conversation


Milton Speer, Visiting Fellow, School of Mathematical and Physical Sciences, University of Technology Sydney and Lance M Leslie, Professor, School of Mathematical And Physical Sciences, University of Technology Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The outlook for coral reefs remains grim unless we cut emissions fast — new research


Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Christopher Cornwall, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, University of AmsterdamThe twin stress factors of ocean warming and acidification increasingly threaten coral reefs worldwide, but relatively little is known about how various climate scenarios will affect coral reef growth rates.

Our research, published today, paints a grim picture. We estimate that even under the most optimistic emissions scenarios, we’ll see dramatic reductions in coral reef growth globally.
The good news is that 63% of all reefs in this emissions scenario will still be able to grow by 2100.

But if emissions continue to rise unabated, we predict 94% of coral reefs globally will be eroding by 2050. Even under an intermediate emissions scenario, we project a worst-case outcome in which coral reefs on average will no longer be able to grow vertically by 2100.

The latter scenarios would have dramatic consequences for marine biodiversity and the millions of people who depend on healthy, actively growing coral reefs for livelihoods and shoreline protection. This highlights the urgency and importance of acting now to drastically reduce carbon dioxide emissions.

Coral reefs are home to more than 830,000 species and provide coastal communities with food and income through fisheries and tourism.

The Great Barrier Reef alone contributes A$6.4 billion to the Australian economy. Critically, coral reefs also protect coastlines from storm surges and create land for many low-lying Indo-Pacific island nations.

Marine heatwaves, caused by ongoing ocean warming, have already had a severe impact on coral reef ecosystems by triggering mass bleaching events. These events are becoming more frequent and intense, and cause mass die-offs across large areas.

Bleaching at the Great Barrier Reef
Marine heatwaves trigger mass bleaching and coral die-offs.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Ocean acidification also reduces the growth of corals by limiting their ability to build their skeletons from calcium carbonate. Together, these stressors threaten the ability of coral reefs to grow and keep up with sea level rise.

Complex impacts from ocean warming and acidification

Our understanding of how ocean warming and acidification threaten reef-forming species has improved considerably over the past decade. However, understanding how coral reef growth will be altered by climate change is more complex than simply measuring rates of change from individual taxonomic groups of corals.

Our study of 183 reefs worldwide provides the first quantitative estimate of how most of the processes that control reef growth respond to climate change and affect carbonate accumulation and growth rates.

Coral reef
Coral on the Great Barrier Reef during the 2020 bleaching event.
Morgan Pratchett, ARC Centre of Excellence for Coral Reef Studies, CC BY-ND

Reefs grow by layering calcium carbonate, produced either by corals and coralline algae. The amount of calcium carbonate built by these reefs depends on many factors.

Cyclones, waves and currents can flush parts of the reef away. Acidifying ocean water means more dissolves chemically. And there is a biological carbonate exchange, known as bio-erosion. Sponges, parrotfish, sea urchins and algae can all eat it, but then return some as defecated sand.

Depending on which of these processes dominates, coral reefs either grow and accrete vertically, or they start to erode. Most of these processes vary for each reef, and almost all are affected by climate change.




Read more:
The Great Barrier Reef outlook is ‘very poor’. We have one last chance to save it


To complicate matters, the frequency and intensity of marine heatwaves will vary geographically, making it difficult to estimate to what degree coral mass bleaching events will reduce coral cover.

In our research, we applied these local and global processes to 233 locations on 183 distinct coral reefs that vary in their species compositions and physical complexity. We found significant variability in responses to ocean acidification and warming.

Geographical and species variability

We predict coral mass bleaching events will have the largest impact on carbonate production across all sites. The world’s coral reefs have already been transformed dramatically by these events over the past few decades.

Coral bleaching at the Maledives
Coral reef in the Maldives, before coral mass bleachign event.
Chris Perry, CC BY-ND



Read more:
We just spent two weeks surveying the Great Barrier Reef. What we saw was an utter tragedy


Diver and equipment at a coral reef
Experimental setup used to measure calcification coralline algae on the Great Barrier Reef.
Guillermo Diaz-Pulido, CC BY-ND

We used the documented impacts of the 2016 mass bleaching on the Great Barrier Reef, which affected a large range of reefs with different species compositions, depths and latitudes. During this event, each reef experienced varying heat stress, which manifested in different levels of coral cover loss.

This information helped us to calibrate models to predict heat-stress events globally between now and 2100 and to gauge the future magnitudes of heat stress and their impact on our study sites.

We found currently degraded reefs fared poorly in our model, even under lower emissions scenarios. Reefs whose carbonate production was more robust against the effects of climate change tended to be those with high present-day carbonate production rates, higher contributions from coralline algae (which are also vulnerbable, but comparatively more resistant to warming than corals) and low rates of bio-erosion.

Hope for coral reefs

In higher emissions scenarios, even reefs dominated by coralline algae began to suffer as ocean acidification and warming intensified. It is also important to note that such reefs will provide different, and perhaps reduced, services compared to coral-dominated reefs because they are structurally less complex.

People standing on a coal reef
Team members assess coral health during the 2016 bleaching event in the Kimberley, Western Australia.
Christopher Cornwall, CC BY-ND

We did not explore in depth whether remaining coral reef communities could gain tolerance to rising temperatures over time. This could manifest as an increase in the proportional abundance of heat-tolerant species as more heat-sensitive corals die during mass bleaching events.

Surviving corals could acclimatise or even adapt. But whether these mechanisms could provide hope for the continued growth of coral reefs in the future — and if so, to what extent — is largely unknown. Nor can we say if more heat-tolerant corals could sustain similar rates of reef growth and structural complexity.

Coral reef in Chagos
A coral reef in Chagos before a bleaching event in April 2016.
Chris Perry, CC BY-ND

The best hope to save coral reefs and their ecological, societal and economic benefits is to reduce our carbon emissions dramatically, and quickly. Even under our projected intermediate scenarios we expect mean global erosion of coral reefs.

Under the lowest emissions scenario we examined, we expect profound changes in coral reef growth rates and their ability to provide ecosystem services. In this scenario, only some reefs will be able to keep pace with rising sea levels.

We owe it to our children and grandchildren to reduce emissions now, if we have any hope of them witnessing the majestic nature of coral reef ecosystems.The Conversation

Christopher Cornwall, Rutherford Discovery Fellow, Te Herenga Waka — Victoria University of Wellington and Verena Schoepf, Assistant Professor, University of Amsterdam

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Storm warning: a new long-range tropical cyclone outlook is set to reduce disaster risk for Pacific Island communities



Photobank.kiev.ua/Shutterstock

Andrew Magee, University of Newcastle; Andrew Lorrey, National Institute of Water and Atmospheric Research, and Anthony Kiem, University of Newcastle

Tropical cyclones are among the most destructive weather systems on Earth, and the Southwest Pacific region is very exposed and vulnerable to these extreme events.

Our latest research, published today in Scientific Reports, presents a new way of predicting the number of tropical cyclones up to four months ahead of the cyclone season, with outlooks tailored for individual island nations and territories.

A new model predicts tropical cyclone counts up to four months in advance.

Tropical cyclones produce extreme winds, large waves and storm surges, intense rainfall and flooding — and account for almost three in four natural disasters across the Southwest Pacific region.

Currently, Southwest Pacific forecasting agencies release a regional tropical cyclone outlook in October, one month ahead of the official start of the cyclone season in November. Our new model offers a long-range warning, issued monthly from July, to give local authorities more time to prepare.

Most importantly, this improvement on existing extreme weather warning systems may save more lives and mitigate damage by providing information up to four months ahead of the cyclone season.

This map shows the expected number of tropical cyclones for the 2020/21 Southwest Pacific cyclone season (November to April).
http://www.tcoutlook.com/latest-outlook, Author provided

Tropical cyclones and climate variability

An average of 11 tropical cyclones form in the Southwest Pacific region each season. Since 1950, tropical cyclones have claimed the lives of nearly 1500 and have affected more than 3 million people.

In 2016, Cyclone Winston, a record-breaking severe category 5 event, was the strongest cyclone to make landfall across Fiji. It killed 44 people, injured 130 and seriously damaged around 40,000 homes. Damages totalled US$1.4 billion — making it the costliest cyclone in Southwest Pacific history.




Read more:
Winston strikes Fiji: your guide to cyclone science


Tropical cyclones are erratic in their severity and the path they travel. Every cyclone season is different. Exactly where and when a tropical cyclone forms is driven by complex interactions between the ocean and the atmosphere, including the El Niño-Southern Oscillation, sea surface temperatures in the Indian Ocean, and many other climate influences.

Capturing changes in all of these climate influences simultaneously is key to producing more accurate tropical cyclone outlooks. Our new tool, the Long-Range Tropical Cyclone Outlook for the Southwest Pacific (TCO-SP), will assist forecasters and help local authorities to prepare for the coming season’s cyclone activity.

This map shows the probability of below or above-average tropical cyclones for the 2020/21 Southwest Pacific cyclone season.
http://www.tcoutlook.com/latest-outlook, Author provided

According to the latest long-range sea surface temperature outlook, there is a 79% chance that La Niña conditions could develop before the start of the 2020-21 Southwest Pacific cyclone season. La Niña conditions typically mean the risk of tropical cyclone activity is elevated for island nations in the western part of the region (New Caledonia, Solomon Islands and Vanuatu) and reduced for nations in the east (French Polynesia and the Cook Islands). But there are exceptions, particularly when certain climate influences like the Indian Ocean Dipole occur with La Niña events.




Read more:
India’s cyclone Fani recovery offers the world lessons in disaster preparedness


Improving existing tropical cyclone guidance

Current guidance on tropical cyclones in the Southwest Pacific region is produced by the National Institute of Water and Atmospheric Research, the Australian Bureau of Meteorology and the Fiji Meteorological Service. Each of these organisations uses a different method and considers different indices to capture ocean-atmosphere variability associated with the El Niño-Southern Oscillation.

Our research adds to the existing methods used by those agencies, but also considers other climate drivers known to influence tropical cyclone activity. In total, 12 separate outlooks are produced for individual nations and territories including Fiji, Solomon Islands, New Caledonia, Vanuatu, Papua New Guinea and Tonga.

Other locations are grouped into sub-regional models, and we also provide outlooks for New Zealand because of the important impacts there from ex-tropical cyclones.

Our long-range outlook is a statistical model, trained on historical relationships between ocean-atmosphere processes and the number of tropical cyclones per season. For each target location, hundreds of unique model combinations are tested. The one that performs best in capturing historical tropical cyclone counts is selected to make the prediction for the coming season.

At the start of each monthly outlook, the model retrains itself, taking the most recent changes in ocean temperature and atmospheric variability and attributes of tropical cyclones from the previous season into account.

Both deterministic (tropical cyclone numbers) and probabilistic (the chance of below, normal or above average tropical cyclone activity) outlooks are updated every month between July and January and are freely available.The Conversation

Andrew Magee, Postdoctoral Researcher, University of Newcastle; Andrew Lorrey, Principal Scientist & Programme Leader of Climate Observations and Processes, National Institute of Water and Atmospheric Research, and Anthony Kiem, Associate Professor – Hydroclimatology, University of Newcastle

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The Great Barrier Reef outlook is ‘very poor’. We have one last chance to save it



Tourists snorkelling on the Great Barrier Reef, the outlook for which has been officially rated “very poor”.
AAP

Terry Hughes, James Cook University

It’s official. The outlook for the Great Barrier Reef has been downgraded from “poor” to “very poor” by the Australian government’s own experts.

That’s the conclusion of the latest five-yearly report from the Great Barrier Reef Marine Park Authority, released on Friday. The report assessed literally hundreds of scientific studies published on the reef’s declining condition since the last report was published in 2014.

The past five years were a game-changer. Unprecedented back-to-back coral bleaching episodes in 2016 and 2017, triggered by record-breaking warm sea temperatures, severely damaged two-thirds of the reef. Recovery since then has been slow and patchy.

Fish swimming among coral on the Great Barrier Reef.
AAP

Looking to the future, the report said “the current rate of global warming will not allow the maintenance of a healthy reef for future generations […] the window of opportunity to improve the reef’s long-term future is now”.

But that window of opportunity is being squandered so long as Australia’s and the world’s greenhouse gas emissions continue to rise.

The evidence on the reef’s condition is unequivocal

A logical national response to the outlook report would be a pledge to curb activity that contributes to global warming and damages the reef. Such action would include a ban on the new extraction of fossil fuels, phasing out coal-fired electricity generation, transitioning to electrified transport, controlling land clearing and reducing local stressors on the reef such as land-based runoff from agriculture.




Read more:
Meet the super corals that can handle acid, heat and suffocation


But federal Environment Minister Sussan Ley’s response to the outlook report suggested she saw no need to take dramatic action on emissions, when she declared: “it’s the best managed reef in the world”.

Major coral bleaching events in 2016 and 2017 have devastated the reef.

The federal government’s lack of climate action was underscored by another dire report card on Friday. Official quarterly greenhouse gas figures showed Australia’s greenhouse gas emissions have risen to the highest annual levels since the 2012-13 financial year.

But rather than meaningfully tackle Australia’s contribution to climate change, the federal government has focused its efforts on fixing the damage wrought on the reef. For example as part of a A$444 million grant to the Great Barrier Reef Foundation, the government has allocated $100 million for reef restoration and adaptation projects over the next five years or so.

Solutions being supported by the foundation include a sunscreen-like film to float on the water to prevent light penetration, and gathering and reseeding coral spawn Separately, Commonwealth funds are also being spent on projects such as giant underwater fans to bring cooler water to the surface.

But the scale of the problem is much, much larger than these tiny interventions.




Read more:
Extreme weather caused by climate change has damaged 45% of Australia’s coastal habitat


Climate change is not the only threat to the reef

The second biggest impact on the Great Barrier Reef’s health is poor water quality, due to nutrient and sediment runoff into coastal habitats. Efforts to address that problem are also going badly.

This was confirmed in a confronting annual report card on the reef’s water quality, also released by the Commonwealth and Queensland governments on Friday.

The Great Barrier Reef attained world heritage status in the 1980s.
AAP

It showed authorities have failed to reach water quality targets set under the Reef 2050 Plan – Australia’s long-term plan for improving the condition of the reef.

For example the plan sets a target that by 2025, 90% of sugarcane land in reef catchments should have adopted improved farming practices. However the report showed the adoption had occurred on just 9.8% of land, earning the sugarcane sector a grade of “E”.

So yes, the reef is definitely in danger

The 2019 outlook report and other submissions from Australia will be assessed next year when the UNESCO World Heritage Committee meets to determine if the Great Barrier Reef should be listed as “in danger” – an outcome the federal government will fight hard to avoid.

An in-danger listing would signal to the world that the reef was in peril, and put the federal government under greater pressure to urgently prevent further damage. Such a listing would be embarrassing for Australia, which presents itself as a world’s-best manager of its natural assets.

Environment activists engaged in a protest action to bring attention to the dangers facing the Great Barrier Reef.
AAP

The outlook report maintains that the attributes of the Great Barrier Reef
that led to its inscription as a world heritage area in 1981 are still intact, despite the loss of close to half of the corals in 2016 and 2017.

But by any rational assessment, the Great Barrier Reef is in danger. Most of the pressures on the reef are ongoing, and some are escalating – notably anthropogenic heating, also known as human-induced climate change.




Read more:
Great Barrier Reef Foundation chief scientist: science will lie at the heart of our decisions


And current efforts to protect the reef are demonstrably failing. For example despite an ongoing “control” program, outbreaks of the damaging crown-of-thorns starfish – triggered by poor water quality – have spread throughout the reef.

The federal government has recently argued that climate change should not form the basis for an in-danger listing, because rising emissions are not the responsibility of individual countries. The argument comes despite Australia having one of the highest per capita emissions rates in the world.

But as Australia’s greenhouse gas emissions continue to rise – an outcome supported by government policy – the continued downward trajectory of the Great Barrier Reef is inevitable.The Conversation

Terry Hughes, Distinguished Professor, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.