David Jones, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Chantal Donnelly, Australian Bureau of Meteorology; Lynette Bettio, Australian Bureau of Meteorology, and Matthew Coulton, Australian Bureau of Meteorology
After the intensely dry conditions of 2019, January and February have brought much-needed rain. Dams in many cities and towns were replenished and some farmers may be able to grow a crop for the first time in several seasons. So does this mean the drought has broken?
The answer is not straightforward. There is no single definition of drought, and the impact of rain varies enormously depending on where it falls.
The assessment of drought conditions involves not just rainfall, but other factors such as water supplies and soil moisture.
The Bureau of Meteorology reports on “meteorological drought” – that is, drought considered purely from the perspective of rainfall deficits. Totals in the lowest 10% of historical observations are considered a serious to severe rainfall deficiency. The bureau does not have responsibility for declaring drought, which is complex and reflects both demand and supply of water, as well as social and economic factors.
In the three years to January 2020 some 33% of Australia and 96% of New South Wales had serious or severe rainfall deficiencies. In the most-affected regions, rainfall over the past three years was around half the long-term average.
Based on rainfall so far in February, the areas suffering serious to severe deficiencies has only slightly improved (to around 30% of Australia and 90% of NSW).
In other words, while some areas have seen excellent rainfall, others have not – so the overall relief from meteorological drought so far this year is modest.
To understand the impact of the recent rain, we need to understand the extent of the drought gripping much of the continent.
Last year was Australia’s driest on record, intensifying one of the most severe droughts of the past century.
In eastern Australia, the dry contributed to the severe 2019-20 fire season. It also challenged town water supplies, and contributed to mass fish die-offs, falls in agricultural production and drying wetlands.
The dry conditions were intense and persistent. The Murray-Darling Basin experienced above-average rainfall in just five months from 2017 to 2019. The total three-year rainfall was a record low 917mm – that’s 548mm below average.
Dry conditions have also affected all east coast urban regions south of Townsville, including Brisbane, Sydney, Canberra and Melbourne.
Rainfall associated with low pressure systems affected Victoria, northeast NSW and inland Queensland in January. Monsoon conditions, coupled with tropical cyclones Claudia and Damien, also marked the late onset of wet season rainfall for tropical areas.
The national rainfall for January was slightly above average (89mm), though NSW, South Australia and the Murray-Darling Basin again recorded below average rainfall overall.
The first half of February has seen good rain across South Australia and inland Western Australia, and heavy rainfall along the east coast (seaward of the Great Dividing Range).
Rainfall was heavy around Sydney, the Illawarra and northeast NSW/southeast Queensland. Several local rainfall records were broken, while Sydney saw a remarkable 392mm fall over four days – more than the city received in the second half of 2019.
But the rain did not fall evenly across the eastern states. Many places in southern and western NSW have received only patchy falls. For example, Broken Hill has received just 8mm since the start of the year. These areas will need more rain to ease drought conditions.
Drought is not just about rainfall but also about the water available in dams, in the soil and in our groundwater systems.
At the end of 2019, soil moisture reserves across large parts of the country were close to zero. In recent weeks, absolute soil moisture across Queensland, NSW, South Australia and Victoria has improved.
While the east coast is now generally very wet, conditions are more varied inland reflecting the patchy nature of summer storms.
Inland rain led to local flash-flooding and triggered high river flows in several areas. Previously dry stretches of the Condamine River in Queensland have flooded, and the Namoi and Castlereagh Rivers in NSW have had their first flows in many months.
A small volume of water will likely make it down the Darling, it will take more than a month. This is because losses to evaporation and seepage into the riverbed will be high.
But not enough rain has fallen in the right places to significantly impact dam levels in northern NSW, which have been critically low over the past year.
Collectively, storage volumes in major dams in the northern Murray Darling Basin have only increased by around 5%. The heaviest inland rain was downstream on the plains rather than on the western slopes of the Great Dividing Range, which feed the dams.
There have, however, been notable increases in dam levels along the east coast where the best rain fell. Since the start of February, water storage volumes have increased from 42% to 79% in the Greater Sydney region and from 56% to 67% in south east Queensland.
Some areas have seen heavy rainfall which has brought drought relief. But others will need more rain in coming months to ease drought conditions.
A natural climate driver, known as the Indian Ocean Dipole, fuelled very dry conditions in Australia in the second half of 2019. That event has now finished, and climate drivers are expected to remain “neutral” in the coming months. This means they are not expected to strongly influence our weather and climate.
The autumn 2020 rainfall outlook shows a mixed picture. In the northern and inland western areas of the continent above-median rainfall is favoured.
Elsewhere, the probability of above-median rainfall is near or below 50%. This suggests drought relief may be slow and patchy overall.
David Jones, Climate Scientist, Australian Bureau of Meteorology; Andrew B. Watkins, Head of Long-range Forecasts, Australian Bureau of Meteorology; Chantal Donnelly, Head of Water Investigations, Australian Bureau of Meteorology; Lynette Bettio, Senior Climatologist, Australian Bureau of Meteorology, and Matthew Coulton, Manager Water Sector Engagement, Australian Bureau of Meteorology
Summer in Australia is getting hotter. Extreme heat events, with daytime temperatures over 35 degrees Celsius, are becoming more common and we are getting more of these days in a row.
We all need to prepare ourselves, our homes and our neighbourhoods for hot and very hot days. Since 2016, the Cooling the Commons research project has been working with people living in some of Sydney’s hottest neighbourhoods to learn how they cope with heat.
Discussion groups with residents across hotspots in Western Sydney, including Penrith, Cranebrook and St Marys, highlighted a wealth of things we can do to manage heat. We published some of the following tips in a recent flier.
Official advice for extreme heat is often to stay inside and turn on the air conditioning. While air conditioning can play a role, not everyone can afford it. Low-income and older households can be especially vulnerable to bill shock and are more likely to feel the impacts of extreme heat.
There is also the risk that running air conditioners uses energy resources that contribute further to global warming. More immediately, hot exhaust air from air-conditioning units can make the local environment hotter. This means keeping one home cool can make it harder for neighbours to keep their homes cool and make being outside even more uncomfortable.
Air conditioning in private homes creates a cool refuge for only some. Unless those homes have an open-door policy on hot days, many of us will need to find other ways to keep cool. If you do have air conditioning, think about how you could share your air with those near you who might really need it.
Shade is important for creating more comfortable living spaces.
Identify which parts of your home get the most afternoon sun in summer. Can you plant trees or vines, or move a pot plant outside the window to create a green screen? Can you attach awnings to shade the windows?
Low-cost temporary solutions can include attaching light-coloured shade cloth outside the window using removable hooks, or installing heavy drapes or blinds inside. Blankets or even aluminium foil are a low-cost creative way of keeping heat out.
Open up to let in cool air at night
Can you open the windows and doors overnight to let in cooler air? If you are concerned about security, look for options for locking the windows in an open position, or using flyscreens and security grilles on windows and doors.
A low-cost option to keeping flying insects at bay on hot nights is a mosquito net over the window or around the bed.
Use low-cost resources to prepare in advance.
Ceiling or portable fans are one of the best ways to cool your body when it’s hot. But remember fans don’t cool rooms, so turn off the fan when you leave the room or you’re just burning electricity.
Find ice trays and containers to freeze water – cake tins and storage containers are a good option. Putting these in front of a portable fan will mean the fan blows cool air.
Putting a wet face cloth on the insides of your wrists, around your ankles or on the back of your neck will bring down your body temperature. Hanging damp sheets in doorways or in front of a fan will help keep the temperature down – although the trick with the sheets won’t work if it’s a really humid day.
Morning is likely to be the coolest time of the day. Open up your windows and doors to let in the cooler morning air.
It’s the best time to be active – walk the dog, take the kids to the park, go for a swim. If possible, do your cleaning, cooking or outside work now. Plan meals that don’t require an oven.
Close up as it heats up.
As the day starts to get hot, close the house up – shut windows, blinds and curtains. This could be as early as 9am on really hot days. If you are heading out to work, do this before you leave home.
Closing internal doors can help to keep the heat in one part of your home. You need to close doors to any parts of the home that get hot before the day gets hot.
Drink plenty of water throughout the day. Put a jug of tap water in the fridge and remember to top it up.
Don’t forget to move pet water bowls and day beds out of the sun. If you live in a dry area, it can’t hurt to put out extra water bowls for needy wildlife!
Find a cooling refuge.
If your home gets uncomfortably hot, find the closest cooling refuges in your neighbourhood. These are places where you can go to cool down. Good examples that won’t break the bank are the local swimming pool or library.
Save air conditioning for when it’s most needed.
Try to save air conditioning for the hottest parts of the day. It will be most effective and cheapest to run if your home is well insulated and you’ve closed it up for the day.
Look after neighbours.
Remember to check on elderly or frail neighbours. Along with the very young, they are usually more affected by the heat and may need to cool down sooner than you do.
If your neighbours are in need, consider inviting them into your home to cool down. When it’s hot, let’s think of our cities as social commons rather than a collection of private spaces.
Emma Power, Senior Research Fellow, Geography and Urban Studies, Western Sydney University; Abby Mellick Lopes, Associate Professor, Design, School of Humanities and Communication Arts, Western Sydney University, and Louise Crabtree, Associate Professor, Institute for Culture and Society, Western Sydney University
The level of water stored by Australia’s capital cities has steadily fallen over the last six years. They are now collectively at 54.6% of capacity – a decline of 30% from 2013.
The results show that Darwin’s water supply has lost about 25% over the last year. On the plus side, Melbourne’s supply actually increased over 2019, having fallen below 50% earlier this year, and now sits on 63.9%.
While the national average is trending downwards, the patterns for each city are very different. Sydney and Perth water supplies have had contrasting journeys over the last six years. In October 2013 Perth’s supply was a very low 33.8% and Sydney was a comfortable 91%.
Now, for the first time in many years Perth does not have Australia’s lowest level of all capital city water storages. As of last week, Sydney has taken this unwanted distinction from Perth.
For Perth residents, the news is good as their surface water storages are at a six-year high of 46.4%. In Sydney they are worried, as they have a six-year low of 46.2%.
Sydney has experienced a steep decline over the last 30 months, from nearly full storages (96%) in April 2017. The speed and severity of the Sydney drought is starting to resemble previous dry spells. One was in the 1940s and the other was the Millennium drought.
Perth has lived with the most water stress of any capital city. They have had to contend with a steady 45-year decline in rain. The inflow of water into Perth’s dams has also fallen dramatically.
Perth has adapted to its drying climate by sourcing water from many different supplies. It now uses its surface water storages for about 10% of its water supply. Much larger proportions of Perth’s supply comes from its two desalination plants, which unlike the other capitals are constantly in operation. It makes greater use of groundwater and highly treated recycled water. Perth also has permanent water restrictions.
Sydney’s desalination plant, after hibernating for 7 years, is now supplying water. It was switched on in late January 2019 when Sydney supply hit 60%, and can supply 15% of water demand. Unusually perhaps, the desalinated water does not reach all parts of Sydney.
Melbourne and Brisbane water supplies are currently at similar levels. However, since 2013 Melbourne’s storages have generally been lower than Brisbane’s. Melbourne’s supply has risen in 2019 after good winter rainfall in its catchments. The storages have increased from under 50% (49.6%) in late May 2019. Today, Brisbane storage levels are now at 59.2%.
Melbourne residents use less water than the other capital cities. In 2018 the average Melbourne resident used 161 litres per day, approximately 30% less than Sydney residents.
Melbourne’s supplies have also been supplemented with the reactivation of its Wonthaggi desalination plant in 2019. It is Australia’s largest desalination plant, capable of producing 410 million litres a day.
Brisbane also built a desalination plant after the Millennium Drought. In addition, they also made very large investments in Australia’s largest waste water recycling scheme. The Western Corridor recycled water scheme opened in 2008, cost $2.5 billion and features three advanced waste water treatment plants, with more than 200 km of pipelines and three advanced waste water treatment plants.
Hobart, Darwin and Canberra are the three Australian capital cities without desalination plants. Canberra has had a steady decline in its supply over three years. It was full in October 2016, gradually dropping to 51.6% in November 2019. Hobart’s storages were above 80% for most of the last six years. They were just above 90% 12 months ago and have since fallen to their current level of 72%.
Darwin’s water supply was full as recently as April 2018. Now, 18 months later, it is just touching 54%. This is its lowest level in six years. Darwin, our tropical capital, has the most seasonal rainfall of Australia’s capitals. Typically, they have almost no rain June to September during their dry season, and a wet season of heavy rains from October to April.
However, the last wet season was one of the driest on record.
Adelaide’s water storage has fluctuated over the last 6 years. Adelaide gets more rain in winter and has dry summers, an opposite pattern to that of Darwin. Over the last 3 years the level has dropped from over 97% in October 2017 to just below 58%.
The desalination plant in Adelaide can supply up to 50% of its water supply. It has been operating in 2019, although not in the wetter months of July and August. The Murray also continues to supply a large proportion of Adelaide’s water supply. The Commonwealth has agreed to use drought funding for the Adelaide desalination plant, so more river water can be used by farmers upstream to grow fodder for livestock.
Australia is set for a dryer and hotter summer than average, particularly in the east. Coupled with continued high levels of household demand, we can expect further declines in water storage levels through the first half of 2020.
Summer is likely to start off hot and dry, according to the Bureau of Meteorology’s summer outlook, released today.
Much of eastern Australia is likely to be hotter and drier than average, driven by the same climate influences that gave us a warmer and drier than average spring.
But these patterns will break down over summer, meaning these conditions may ease for some areas in the second half of the season. Despite this, we’re still likely to see more fires, heatwaves, and dust across eastern Australia in the coming months.
Our current weather comes in the context of a changing climate, which is driving a drying trend across southern Australia and general warming across the country.
In southern Australia, rain during the April to October “cool season” is crucial to fill dams and grow crops and pasture. However, like 17 of the previous 20 cool seasons, 2019 was well below average, meaning a dry landscape leading into the summer months.
The frequency of high temperatures has also increased at all times of year, with the greatest increase in spring.
But summer, like spring, will also be influenced by two other significant climate drivers: a change in ocean temperatures in the Indian Ocean, and warm winds above Antarctica pushing our weather systems north.
The first driver is a near-record strong positive Indian Ocean Dipole (IOD). A positive IOD occurs when warmer than average water develops near the Horn of Africa, and cooler waters emerge off Indonesia.
This pattern draws moisture towards Africa – where in recent weeks they have seen flooding and landslides – and produces higher pressures over central and southern Australia. This means less rain for Australia in winter and spring.
Usually the IOD events break down by early summer, when the monsoon arrives in the southern hemisphere. However, this year the monsoon has been very sluggish moving south – in fact it was the latest retreat on record from India – and international climate models suggests the positive IOD may not end until January.
The other unusually persistent climate driver is a negative Southern Annular Mode (SAM), which means weather systems over the Southern Ocean – the fronts and lows and wild winds – are further north than usual. This means more days of westerly winds for Australia.
In western Tasmania, where those winds are coming off the ocean, it means cooler and wetter weather. In contrast, in southeast Queensland and New South Wales, where westerlies blow across long fetches of land, this air is dry and hot.
This persistent period of negative SAM in 2019 was triggered by a sudden warming of the stratosphere above Antarctica – a rare event identified in early September.
Models suggest the negative SAM will decay in December. This means the second half of summer is less likely to be influenced by as many periods of these strong westerlies.
But while both these dry climate drivers are expected to be gone by midsummer, their legacy will take some time to fade.
The positive IOD and the dry conditions we have seen in winter and spring are associated with severe fire seasons for southeast Australia in the following summer.
And while the drying influences are likely to ease, the temperature outlook indicates that days are very likely to remain warmer than average.
We also know that any delay in the monsoon will keep air drier for longer across Australia, and potentially aid in heating up the continent.
For areas of southern Queensland and northeastern NSW, the wet season will eventually bring seasonal rains, although heatwaves are likely to continue through summer.
So, while the outlook for below average rainfall may ease over summer months for some areas, the lead-up to summer means Australia’s landscape is already very dry. Even a normal summer in the south will mean little easing of the dry until at least autumn.
With dry and hot conditions looking likely this summer, it’s important to stay safe, have an emergency plan in place, look after your friends and neighbours in the hot times, and always listen to advice from your local emergency services.
President Donald Trump has reportedly suggested on more than one occasion that the US military explode nuclear bombs inside hurricanes to disrupt them before they reach land.
On the surface, it would seem like a simple solution to the devastation that occurs in the US each year during the hurricane season. However, there are several problems with this idea.
Hurricanes are low-pressure weather systems covering an area of more than 500,000km². They form over warm tropical oceans, which are their primary energy source. The low pressure at the centre of the hurricane – the eye – draws in the surrounding warm, moist air. This air then rises and condenses into deep thunderstorm clouds surrounding the centre – the eyewall – and also in cloud bands spiralling out from the eye called rainbands.
As the air is pulled into the eye, Earth’s rotation causes it to spin cyclonically – anticlockwise in the northern hemisphere and clockwise in the southern hemisphere. The continuous supply of air into the deep thunderstorms surrounding the eye allows the hurricane to intensify until it reaches a steady state of equilibrium with the oceans and the environment.
The average hurricane can be likened to a very inefficient heat engine. As the warm moist air rises, it releases heat energy through the formation of clouds and rain at a rate of about 5.2 x 10¹⁹ joules per day. Less than 10% of this heat is then converted into the mechanical energy of the wind.
To give some perspective of this energy, the heat released in a hurricane is equivalent to a 10-megatonne nuclear bomb exploding every hour. This energy is also on the order of the global energy consumption in 2016, according to the United States Energy Information Agency.
It seems unlikely that exploding a bomb in the hurricane would make much impact on such a powerful weather system, and it is impossible to run controlled experiments to determine whether it would.
Not to mention that there could be shocking effects from the fallout of radioactive material from such an explosion. These materials would be transported widely via the trade winds through the lower levels of the atmosphere, and potentially around the entire planet in the stratosphere – similar to the effects from the volcanic fallout from Mount Pinatubo in the Philippines in 1991.
There have been previous attempts to modify the impacts of hurricanes. Between 1962 and 1983 the US government funded experimental research on hurricane modification known as Project STORMFURY. The fundamental premise was, because the potential of damage from hurricanes increases rapidly with the hurricane’s wind speed, a reduction in wind speed of as little as 10% could make a large difference in the impacts when hurricanes reach land. By seeding the air outside the eyewall with silver iodide, a chemical used to seed clouds, it was thought a new ring of thunderstorms may develop outside the eyewall – robbing it of energy and weakening the hurricane.
Modification was attempted in four hurricanes on eight different days. On four of those days, a 10-30% reduction in wind speed was measured. The lack of response on the other fours days was initially interpreted to be the result of faulty execution of the experiment, but was later attributed to an imperfect understanding of the microphysics of clouds in hurricanes.
Recent observations show hurricanes have too many naturally occurring ice crystals and too few supercooled water droplets for cloud seeding to be effective. So any change in hurricane wind speed observed during the STORMFURY experiments was almost certainly due to the natural behaviour of hurricanes rather than human intervention.
Although Project STORMFURY was abandoned, the hurricane observation program is still run under the Hurricane Research Division of the National Oceanic and Atmospheric Administration (NOAA). The original aircraft used in Project STORMFURY were replaced in the 1970s by WP-3D aircraft, which still reside under NOAA and are operated by its officers.
The observations collected by these aircraft continuously over a period of more than 60 years has helped improve hurricane forecasting. Furthermore, these observations have allowed researchers to develop vital insights into the structure, intensity, and physical processes of this most destructive of natural phenomena.