Two years ago, New Zealanders were shocked when contaminated drinking water sickened more than 5,000 people in the small town of Havelock North, with a population of 14,000. A government inquiry found that sheep faeces were the likely source of bacterial pathogens, which entered an aquifer when heavy rain flooded surrounding farmland.
A second phase of the inquiry identified six principles of international drinking water security that had been bypassed. Had they been followed, the drinking water contamination would have been prevented or greatly reduced.
Here, I ask if the approach recommended by the Havelock North inquiry to prevent drinking water contamination can be extended to reduce the impacts of nutrient contamination of freshwater ecosystems.
Freshwater degraded and in decline
Most measures of the ecological health and recreational value of New Zealand’s lowland rivers and lakes have been rated as degraded and still declining. Intensive agriculture often cops much of the blame, but primary industry exports remain the heart of New Zealand’s economy.
The challenge posed by this trade-off between the economy and the environment has been described as both enormous, and complex. Yet it is a challenge that New Zealand’s government aims to tackle, and continues to rate as a top public concern.
An important lesson from the Havelock North inquiry is that sometimes there is no recipe – no easy list of steps or rules we can take to work through a problem. Following existing rules resulted in a public health disaster. Instead, practitioners need to follow principles, and be mindful that rules can have exceptions.
For freshwater, New Zealand has a similar problem with a lack of clear actionable rules, and I’ve mapped a direct link between the six principles of drinking water security and corresponding principles for managing nutrient impacts in freshwater.
Six principles for freshwater
Of the six principles of drinking water safety, the first is perhaps the most obvious: drinking water safety deserves a “high standard of care”. Similarly, freshwater nutrient impact management should reflect a duty of care that mirrors the scale of impacts. Our most pristine freshwater, like Lake Taupo, and water on the verge of tipping into nearly irreversible degradation, deserve the greatest effort and care.
Second, drinking water safety follows a clear logic from the starting point: “protecting the integrity of source water is paramount”. For nutrient impact management in freshwater, we must reverse this and focus on a more forensic analysis along flowpaths to the source of excess nutrients entering water. Our current approach of using estimates of sources is not convincing when tracers could point to sources in the same way DNA can help identify who was at a crime scene. We must link impacts to sources.
Third, drinking water safety demands “multiple barriers to contamination”. For freshwater, we’re better off taking a similar but different approach – maximising sequential reductions of contamination. There are at least three main opportunities, including farm management, improving drains and riparian vegetation, and enhancing and restoring wetlands. If each is 50% effective at reducing contaminants reaching waterways, the three are as good as a single barrier that reduces contamination by 90%. The 50% reductions are likely to be much more achievable and cost effective.
Managing hot spots and hot moments
The fourth principle of drinking water safety was perhaps the most dramatic failure in the Havelock North drinking water crisis: “change precedes contamination”. Despite a storm and flood reaching areas of known risk for contaminating the water supply, there were no steps in place to detect changing conditions that breached the water supply’s classification as “secure” and therefore safe.
A similar, but inverted principle can keep nutrients on farm, where we want them, and keep them out of our water. Almost all processes that lead to nutrient excess and mobilisation, as well as its subsequent removal, occur in hot spots and hot moments.
This concept means that when we look, we find that roughly 90% of excess nutrients come from less than 10% of the land area, or events that represent less than 10% of time. We can identify these hot spots and hot moments, and classify them into a system of control points that are managed to limit nutrient contamination of freshwater.
Establishing clear ownership
A fifth principle for drinking water seems obvious: “suppliers must own the safety of drinking water”. Clear ownership results in clear responsibility.
Two world-leading cap-and-trade schemes created clear ownership of nutrient contaminants reaching iconic water bodies. One is fully in place in the Lake Taupo catchment, and another is still under appeal in the Lake Rotorua catchment.
These schemes involved government investment of between NZ$70 million and NZ$80 million to “buy out” a proportion of nutrients reaching the lakes. This cost seems unworkable across the entire nation. Will farmers or taxpayers own this cost, or is there any way to pass it on to investors in new, higher-value land use that reduces nutrient loss to freshwater? A successful example of shifting to higher value has been conversions from sheep and beef farming to vineyards.
As yet, the ownership of water has made headlines, but remains largely unclear outside Taupo and Rotorua when it comes to nutrient contaminants. Consideration of taxing the use of our best water could be much more sensible with a clearer framework of ownership for both water and the impacts of contaminants.
The final principle of drinking water safety is to “apply preventative risk management”. This is a scaled approach that involves thinking ahead of problems to assess risks that can be mitigated at each barrier to contamination.
For nutrient management in water, a principled approach has to start with the basic fact that water flows and must be managed within catchments. From this standpoint, New Zealand has a good case for leading internationally, because regional councils govern the environment based on catchment boundaries.
Within catchments we still have a great deal of work to do. This involves understanding how lag effects can lead to a legacy of excess nutrients. We need to manage whole catchments by understanding, monitoring and managing current and future impacts in the entire interconnected system.
If we can focus on these principles, government, industry, researchers, NGOs and the concerned public can build understanding and consensus together, enabling progress towards halting and reversing the declining health and quality of our rivers and lakes.
In April last year, this column looked at six concerns about the planned release of carp herpes virus (Cyprinid herpesvirus 3 or CyHV-3 – also known as koi herpesvirus, or the carp herpesvirus) into Australian rivers in an attempt to dramatically reduce the plague proportions of these introduced and destructive “river rabbits”. Radio JJJ also broadcast a special report in May on “what could possibly go wrong”.
In the eight months since, the NSW government has held public consultations with interested parties and the Australian government’s Department of Industry published a final report late last year.
This report concentrated on whether the virus might impact other fish and native species. It concluded:
Following clinical, molecular and histological observations, we now know that CyHV-3 does not infect (and therefore cannot affect) a wide taxonomic range of non-target animals including: 14 species of fish (13 native species, and the introduced rainbow trout); yabbies; a species of lamprey; two amphibian species; two reptile species; chickens; and mice. These results strongly suggest that both spillover infections and species jumps are highly unlikely with CyHV-3, and, therefore, the results encourage further work on the use of CyHV-3 as a potential biocontrol agent for carp in Australia.
The report also discusses a planned infected carp release into the Lachlan river catchment area in NSW. The Lachlan flows some 1,440km with its main stream and tributaries passing towns that include Cowra, Forbes, Condobolin, Lake Cargelligo, Hillston, Booligal, and Oxley.
Concerns about the release of CyHV-3 possibly affecting other aquatic species has been a major issue and these findings may provide some assurance of safety.
However, in my 2016 column, I noted the carp-deadly herpes virus had first “appeared” in Israel in 1998 and had since migrated to 33 nations through fish commerce. This seemingly innocuous “appeared” word, read in conjunction with the normal never-say-never, careful language of science in the government final report (“strongly suggest”, “highly unlikely”) raise questions about the provenance of the new virus before it first “appeared” in Israel.
If the 1998 appearance was a mutation of a previously benign virus, obvious questions arise about future mutations, including whether such changes might be capable of jumping species once the virus is released into NSW rivers.
The current situation appears to be full steam ahead with a gung-ho Barnaby Joyce publicly making statements about plans to start the release at the end of 2018. $15m has been budgeted for the exercise.
Mini “stench rehearsal” at Hindmarsh Island
This week, ABC News reported “hundreds” of dead carp had washed up on Hindmarsh Island near the sea in South Australia. Blackwater from decomposing vegetation washing into the Murray-Darling during the 2016 floods making its way downstream is seen as responsible for the fish kills. A local resident emphasised the stench. Her words were important and portend a major concern I raised in my column last year.
Catharina Taylor told the ABC the dead and rotting carp were causing a “horrible smell” and she feared the smell would get worse in the summer heat.
She had alerted both her local council and the South Australian State Government’s Primary Industries and Regions department about the problem, who offered no help: “Only thing that I actually heard is that they cannot help, they haven’t got the manpower and we should get the community behind us,” Ms Taylor told the ABC.
Photos in the ABC report show hundreds of dead fish on the shores of the island causing the stench. I have experienced the smell of a single dead carp. It is not an experience easily forgotten. No one has reliable figures about how many carp are in Australian waters, but estimates range from 2-6 million tonnes. The Hindmarsh Island experience will be like a splinter in the handrails of the Titanic compared to the problem the “carpageddon” we are being promised.
A November report in The Land quoted University of Canberra researcher, Dr Peter Unmack, who has two decades of experience working in the Murray-Darling basin. Unmack said disposal of carp carcasses would be a major concern, as decaying fish would pile up from the first week the virus was released. This would de-oxygenate water and harm native fish. “You would need a lot of people in boats with nets scooping up dead fish.”
In all that has been written and said about the release plan, there has been no detail provided about clean up, beyond vague talk about paying locals to remove and dispose of dead fish. The Lachlan is 1,440 kilometres long, the Murrumbidgee 1,600 and the Murray-Darling, 2,507km. Great stretches of these rivers are sparsely populated. No scenarios have been painted about how many people will be needed in the clean-up, covering how many kilometres, in how many boats, and across what length of time will be required to clean it all up. And in these small towns, how many people are sitting about ready to take to the boats?
A “thought bubble” solution”?
Matt Landos, a lecturer in aquatic animal health at the University of Sydney posted important comments on my last column on this issue.
Carp are vilified as a major cause of river turbidity or cloudiness. They suck up mud looking for food. Landos argued the evidence about carp being a major cause of river turbidity is conflicted in the research literature on the issue. In 1985 Fletcher and others said of a Goulburn valley study:
There was no association between high carp densities and high turbidity, and populations of carp did not appear to increase turbidity. Observed turbidity increases at each site appeared to be related to hydrological changes. Fluctuation of water levels was also an important factor determining the extent of aquatic vegetation communities.
Landos also noted King et al (1997) had stated:
factors other than carp usually contributed to most of the variation in measured water quality in Murrumbidgee billabong.
They also observed:
Cattle grazing and clearing has altered the vegetation communities of the floodplain in this region. The floodplain vegetation now consists of scattered mature river red gums. The understorey is dominated by introduced grass and weed species. Owing to the drought conditions and grazing by cattle, vegetation in the catchments surrounding the billabongs was sparse during most of the study period; this and heavy rain towards the end of the experiment combined to cause significant sediment loss from the adjacent hills.
Dr Landos also notes carp are highly unlikely to be the primary driver of native fish declines, though often blamed. To blame carp, is to ignore the swathes of literature on the reasons native fish reproduction has failed including: loss of passage/access due to dams, weirs and irrigation gates; cold water pollution obliterating the spawning signals; pesticides killing and deforming larvae; fertiliser promoting toxic algae; salinity impacting egg hydration; and loss of habitat.
Carp have few friends. Unlike in other parts of the world, few are eaten in Australia. They are an easily scapegoated target. The herpes release seems highly likely to cause massive problems that have to date only been sketched. And all agree that while the release will reduce carp numbers dramatically, it will not eradicate them. If Landos and the researchers he cites are correct, this exercise may do little to improve water quality in our rivers either and may have signiicant collateral impacts.
Fish are the most threatened group among Earth’s freshwater vertebrates. On average, freshwater fish populations have declined by 76% over the past 40 years. Damaged fish communities and declining fisheries characterise global freshwater environments, including those in Australia.
Fish migrate to complete their life cycles, but water-resource developments disrupt river connectivity and migrations, threatening biological diversity and fisheries.
Millions of dams, weirs and smaller barriers – for storage and irrigation, road and rail transport and hydropower schemes – block the migration of fish in rivers worldwide.
These barriers serve our needs for water supply, transport and energy. But, by obstructing fish migrations, they also degrade ecological integrity and reduce food security.
This is bad news for those who depend on fish for food. For example, in the Mekong River fish supply over 70% of the people’s animal protein, but catches are falling drastically following dam building.
In our paper published today in CSIRO’s Marine and Freshwater Research, we take stock of the impact these barriers have on our freshwater fish, most (perhaps all) of which migrate, and how we can help them.
Dam it all
There are countless barriers across Australia’s rivers. Roughly 10,000 barriers of all kinds obstruct flows in the Murray-Darling Basin. Flow is unobstructed in less than half of the basin’s watercourse length.
Native fish numbers in the basin’s rivers have declined by an estimated 90% through habitat fragmentation by barriers together with altered flows, overfishing, coldwater pollution and invasive species.
Similar problems also affect coastal river systems. One or more barriers obstruct 49% of rivers in southeast Australia.
Local species extinctions and loss of biodiversity have occurred nationwide in developed regions, especially upstream of large dams.
One way to help fish overcome barriers is to build fishways (or “fish ladders”).
Fishways are designed to aid fish travelling upstream or downstream at high (dams, weirs) or low (road crossings, barrages) barriers. These are classed as “technical”, with hard-engineering designs, or “nature-like”, mimicking natural stream channels.
Recognition that dams threaten freshwater fish communities lagged well behind their construction. Nonetheless, European and American observations of declining fisheries for species moving from the sea to breed in rivers prompted early attempts in Australia to provide for fish passage.
The first Australian fishway was built near Sydney in 1913. By 1985, 52 had been built, but they adopted Northern Hemisphere designs for salmon and trout. These were unsuitable for Australian species, which rarely leap at barriers, and their flow velocities, turbulence and other aspects were excessive.
Seeing the failure of these fishways, New South Wales Fisheries sought advice in 1982 from George Eicher, an American expert, who advised on research to create designs for local species.
This led to expanding fishways research and construction in eastern states. The result was markedly improved performance, for example in the Murray-Darling’s Sea to Hume program.
Our research shows that regrettably few Australian fishways have yet been shown to meet ideal ecological criteria for mitigating the impact of barriers. Furthermore, fishways are in place at relatively few sites.
In NSW, for example, only about 172 in total serve several thousand weirs and 123 dams. They can be expensive to build and operate, so costs retard mitigation at numerous important sites.
Fishways have seldom been built on dams (fewer than 3% of Australia’s 500 high dams have one); they have generally cost tens of millions of dollars; and most operate, with limited effectiveness, for less than 50% of the time. The need for much greater investment in innovation, research and development is pressing.
How to store water and also rehabilitate fish
To reduce the impact of dams on fish we need to look at resolving problems at river-basin scale; improving our management of barriers, environmental flows and water quality; removing barriers; and developing improved fishway designs.
One way to accelerate improvements nationally would be to pass legislation for routinely re-licensing waterway barriers at regular intervals. This would mean that older barriers are re-evaluated and upgraded or removed where necessary. Under the NSW Weir Removal Program, 14 redundant weirs have already been removed, with others under assessment.
We are developing an innovative pump fishway concept at UNSW Australia. It combines aquaculture fish-pumping methods for safe fish transfer with existing fishway technology.
We hope the project may help transform past practices through less-costly modular construction, adaptability to a wide range of barriers and improved effectiveness.
Better fishway developments will mean that we can store and supply much-needed water while also restoring fish migrations. This will be increasingly important as climate change reduces streamflows in many regions, and will help rehabilitate fish populations.
John Harris, Adjunct Associate Professor, Centre for Ecosystem Science, UNSW Australia; Bill Peirson, Adjunct, Water Research Laboratory, School of Civil and Environmental Engineering, UNSW Australia, and Richard Kingsford, Professor, School of Biological, Earth and Environmental Sciences, UNSW Australia
For much of this year, up to 1,700 kilometres of the Murray River has been hit by a serious outbreak of potentially toxic blue-green algae, which has flourished in the hotter-than-average conditions. After three months, the river is now recovering with the arrival of wet weather. But we are unlikely to have seen the last of these poisonous microbes.
Large blue-green algal blooms are a relatively new phenomenon in inland waterways. In 1991 an algal bloom affected more than 1,000 km of the Darling River, the first time such an event had been reported in an Australian river, and one of the few times internationally. It was an environmental disaster, killing livestock and striking a telling blow against Australia’s reputation as a clean, green farming nation.
The response was decisive: a state of emergency was declared, and the bloom ultimately gave rise to significant investment by state and federal governments into freshwater research, particularly in the Murray-Darling Basin.
Why no emergency now?
Fast forward two and a half decades to the latest bloom afflicting the Murray River, one of Australia’s most socially, economically and culturally significant waterways. The past decade has seen four similar blooms on the Murray River: in 2007, 2009, 2010 and now. Yes, they have garnered press attention, but there has not been the same call to arms that we saw when the Darling River was struck in 1991.
It is almost as if such significant environmental events are now simply seen as the new normal. Why the apparent complacency?
The 2007, 2009 and 2010 algal blooms on the Murray River all happened during the Millennium Drought, and hence were probably ascribed to an aberration in the weather. In reality, the situation may have more to do with how we manage water in Australia – particularly during periods of scarcity, such as the one we may well be entering now.
Those three earlier events all started in Lake Hume, a large reservoir in the Murray River’s upper reaches, originally created in the 1930s to help “drought-proof” Australia. All of the blooms began after the water level was drawn down to below 10% of the lake’s capacity. At these low levels, disturbances (such as when transferring water between the Snowy River and Murray River systems) can easily lead to the mixing of warm surface waters (ideal for bloom formation) with nutrient-rich water at the bottom of the reservoir (ideal for feeding the bloom).
The resulting blooms were then released downstream into the Murray River by managed water releases from Lake Hume. The blooms most likely reformed in other constructed water bodies downstream – most notably Lake Mulwala, a shallow reservoir about 250 km along the river from Lake Hume.
Lake Mulwala’s principal purpose is to create hydraulic pressure to allow irrigation water to be diverted into farmland in southern New South Wales and northern Victoria. As a result, its shallow depth and mostly still waters make it an ideal incubator for blue-green algae.
The climate factor
This year’s algal bloom on the Murray River is different. The main blue-green alga in the current outbreak, Chrysosporium ovalisporum, has previously been reported in the river, but generally in very low numbers. It has never before formed a bloom in the Murray River since monitoring began in 1978. But crucially, this species flourishes in very warm temperatures; overseas blooms of this species have occurred when water temperatures reach 26℃.
The other difference between the current and earlier blooms is that, when this year’s event started, Lake Hume was much fuller, at about 30% capacity. So reservoir operation probably had less to do with the bloom’s formation than other factors, such as the climate. Both the maximum and minimum temperatures were consistently above the long-term average during the past few months, as was the amount of sunlight reaching the surface of Lake Hume.
We still do not know exactly what triggered this year’s bloom, but if it was indeed a result of unusually warm temperatures, it is very likely that we will see more blooms of this type in the future.
Are we really ready for recurrent blue-green algal blooms on the Murray River? These blooms come at a significant economic cost: drinking water has had to be specially treated to remove potential toxins, and the bloom has impacted on regional tourism, coinciding with the Labour Day and Easter long weekends. It also hit farmers, who had to get drinking water for their livestock from elsewhere.
More importantly, what do these frequent blooms say about how we manage water in this country – especially as we start to see the impacts of climate change on our environment? Dwindling water could mean more than just drought – it could also fill much of the water that remains with poisonous microbes.
Everyone wants to give Australian carp the herpes virus. That’s right, introduced carp are a serious pest species and research suggests that a viral control agent may be the most effective solution.
I love stories like this one, where groups that would normally disagree come together in an “unlikely coalition”. That is to say, fishers, conservationists, irrigators, scientists and farmers agree on the desirability of an environmental release of the carp-specific virus.
After all, it worked for rabbits. The release of the myxomatosis virus in the 1950s and the more recent release of calicivirus have permanently decreased rabbit numbers on our continent. Using viral pathogens to control vertebrate pests can be extremely effective because it does not require ongoing human intervention.
Like rabbits, carp were introduced to Australia deliberately. The first introductions in the 1800s did not cause problems, but a strain bred for European aquaculture escaped from farm dams near Mildura in the 1960s and spread throughout the Murray Darling Basin. The impact of carp on our rivers has been well documented, including increasing turbidity (making the water muddy), destroying aquatic vegetation, and contributing to the decline of native fish.
In other parts of the world, carp are an important food species, often raised in fish farms. When I worked on a kibbutz in Israel in 1980 we caught and sorted carp from geothermal pools near the Sea of Galilee. The fish were a desirable food item and water from the fish ponds was used to fertilise banana crops via drip irrigation. I admired the sustainable farming practice that was then ahead of its time.
Twenty years later while participating in a fish survey at Horseshoe Lagoon near Albury, I remember pulling dozens of giant carp out of our nets, lamenting the lack of native fish. Because we were not allowed to return the carp to the water due to its pest status, we had to kill each one, resulting in a large pile of stinky dead fish that nobody wanted to eat.
The only similarity between these two memories was the method of death: although it looks brutal and cruel, hitting carp on the back of the head with a heavy wooden stick dispatches them instantly and humanely. On those two occasions this peaceful vegetarian turned into a lethal killing machine.
Ironically, at about the time I was whacking pest carp in Australia, the carp industry in Israel was affected by a new disease. The koi herpesvirus, or Cyprinid herpesvirus 3 (CyHV-3) appeared in Israel in 1998 and was so contagious that it soon spread throughout Europe and Asia. The carp industry was devastated.
While this virus is bad news for carp farming, it could be good news for managing feral carp in Australia. With an expected mortality rate of 70-80%, CyHV-3 may be just what we need to curb the plague of carp in our rivers.
Of course, given our sometimes disastrous experience with biological control species, caution is warranted. That’s why scientists have spent the last eight years doing research to ensure that the herpes will not affect other species. Ken McColl is a leader of the team that has examined the host specificity of the virus in an Australian context.
The good news is that CyHV-3 has no impact on other native fish, yabbies and trout. It cannot infect mammals, amphibians or reptiles. In other words, it looks safe.
The bad news is that it will affect ornamental carp (koi) which are highly valued, so people who keep koi will need to monitor their water and food sources. I see this as something like vaccinating your pet rabbits against calicivirus, an inconvenient but reasonable impost given the benefit for the nation and our environment.
What happens now? There are a number of government organisations that are responsible for biosecurity. Getting approval to introduce a virus into our waterways will probably take a few years, so the research will continue as the Invasive Animals Cooperative Research Centre goes through the application process.
There is also research underway to identify locations suitable for early releases, and this is where members of the public can get involved. Hotspots for invasive fish species will be identified by gathering data from concerned citizens at a new website called Feral Fish Scan. Anyone interested in learning how to identify invasive fish and record observations of their local waterways can do so at this link.
Other conventional approaches to reducing carp are still underway, from the development of traps that target carp to better ways for Charlie Carp to turn those feral fish into fertiliser. But harvesting tons of carp and turning them into pellets will never reduce the impact of this noxious pest as effectively as a carp-specific disease.
This is why virtually everyone is excited about the possibility of giving herpes to Australian carp. And even though I think it sounds like a good idea, I am also grateful that we have robust regulations about biocontrol, because there was a time when cane toads seemed like a good idea, too.
We can wait a couple of years to ensure that we do not regret our decision, but then we may enjoy a great irony: a disease that caused huge financial losses overseas could save freshwater environments in Australia.
Rising carbon dioxide concentrations are causing vegetation across large parts of Australia to grow more quickly, in turn consuming more water and reducing flows into river basins.
Our research, published today in Nature Climate Change, shows that river flows have decreased by 24-28% in a large part of Australia due to increasing CO₂ levels, which have risen by 14% since the early 1980s.
This could exacerbate water scarcity in several populated and agriculturally important regions.
It was previously unclear whether the increasing CO₂ in the atmosphere has led to detectable changes in streamflow in Australian rivers. This is partly because increasing CO₂ can have two opposing effects on water resources.
CO₂ is the key ingredient for photosynthesis, and higher concentrations allow plants to grow more vigorously. This fertilisation effect could be expected to lead to denser vegetation that needs more water to grow, in turn reducing the amount of rainwater that can run off into rivers.
Acting directly against this is the fact that increased CO₂ concentrations allow plants to use water more sparingly. Small pores called stomata on the surface of leaves allow plants to regulate their uptake of CO₂ for photosynthesis and water loss to the atmosphere. At higher CO₂ concentrations, plants can partially close these pores, maintaining the same influx of CO₂ while also reducing water loss through transpiration. This could be expected to leave more rainwater available to become river runoff.
The net effect of these two counteracting processes has so far been highly uncertain. In our study, we used a new method that combines satellite measurements of vegetation cover with river flow data collected for over 30 years. Using statistical methods we factored out other influences that affect river flows, such as variations in rainfall.
Our results suggest that the net effect of increased CO₂ has been declining runoff across the subhumid and semi-arid parts of Australia, and that this can be attributed to the increased vegetation.
The good news is that increasing CO₂ might also make plants better able to survive in these drying landscapes. By using water more efficiently, plants can grow more vigorously in arid regions and should better withstand droughts, such as those commonly associated with El Niño events. In areas with an average annual rainfall below about 700 mm, we found that the amount of vegetation cover that can be sustained has increased by about 35% since the early 1980s. This is good news for dryland cropping and grazing which are likely to enjoy increased yields as a consequence.
Despite these positive effects, in less dry parts of Australia, the reduction of river flow adds yet more pressure to water resources. As natural vegetation is greening and consuming more water, local rivers and dams are receiving less. At the same time, rainfall patterns are changing. With the exception of northern Australia, many of the affected areas are already experiencing declining rainfall and this trend is projected to continue into the future with increasing global temperature.
Elsewhere around the world, vegetation increases have also been observed in other dry regions such as southern and western Africa and the Mediterranean. It is certainly possible that these regions are also facing declining streamflow as a result.
The increase in vegetation helps to draw CO₂ from the atmosphere, but the effect is not enough to significantly slow the rise in atmospheric CO₂ and the resulting long-term climate change. Despite the observed greening, most of Australia’s vegetation continues to be very sensitive to rainfall changes. If rainfall continues to decline as projected, the greening trend may end or even be reversed, releasing the stored carbon back into the atmosphere.
Anna Ukkola, Research Associate, Climate Change Research Centre, UNSW Australia and Albert Van Dijk, Professor of Water Science and Management, Fenner School of Environment & Society, Australian National University