‘Massive relief’: torrential rain douses bushfires across parts of Australia | World news

Torrential rain in New South Wales has reduced the number of active fires in the state by a third, from more than 60 down to 42.

The commissioner of the NSW Rural Fire Service, Shane Fitzsimmons, said on Friday there had been a “dramatic shift” in the hot, dry and windy conditions that have driven the unprecedented fire season for months.

“This has been an absolute welcome disruption to that weather pattern and a massive reprieve and relief to so many people right across New South Wales,” he said.

“Obviously we don’t want to see lots of widespread damage and destruction from flooding, but it is certainly a welcome change to the relentless campaign of hot, dry weather resulting in widespread damaging, destructive fires that we’ve experienced for too long now.”

The RFS is taking advantage of the conditions to strengthen containment lines and, where possible, conduct back-burning operations.

Fitzsimmons said of the 42 fires still burning in NSW, 17 were uncontained.

He said there was optimism that rainfall over the next week would result in many of those being declared contained, and “hopefully going to the status of out”.

Most of the rain has hit fires in the north and northeast of the state.

“It’s certainly not across all the fire grounds at this stage. We’ve seen it concentrated largely up through the north-east of the state, it is slowly moving south-eastwards toward Sydney and parts of the Illawarra,” Fitzsimmons said.

Coastal areas of NSW, including Sydney, could receive their highest rainfall levels in more than three years as a trough makes its way down the state.

Multiple severe weather and flood warnings were in place across the state on Friday, with emergency services warning of possible land slips in areas near fire grounds cleared of vegetation.

The Bureau of Meteorology said Friday could see Sydney receive its largest amount of rainfall over a 24 hour period since 2018, with 60mm to 90mm forecast.

The last time the city had more than 100mm of rain in one day was 28 November 2018.

Greenhouse gas emissions from burning fossil fuels, forest destruction and other human activities are trapping heat and putting more energy into the climate system. 

Hotter air means heatwaves are much more likely. For example, scientists now say the unprecedented heat and wildfires across the northern hemisphere in 2018 “could not have occurred without human-induced climate change”. In Australia, the scorching summer of 2016-17 in New South Wales was made at least 50 times more likely by global heating, linking it directly to climate change.

Hotter air can also carry more water vapour, meaning more intense rain and more flooding. 

Another important factor in the northern hemisphere is the impact of changes in the Arctic. The polar region is heating more rapidly, reducing the temperature difference with lower latitudes. There is strong evidence that this is weakening the planetary waves (including the jet stream) that normally meander over Europe, Asia and North America.

When these waves stall, weather gets fixed over regions and becomes extreme. This has been linked to past floods in Pakistan, heatwaves in Russia and drought in California. 

Most of the planet’s trapped heat goes into the oceans and rising sea temperatures mean more energy for hurricanes and typhoons. Record-breaking cyclones hit Mozambique in March and April. The deluge delivered in the US by Hurricane Harvey in 2017 was made three times more likely by climate change. Rising sea level also means storms cause more coastal damage.

Global heating does not influence all extreme weather – natural variability still exists. Carbon Brief analysed more than 230 studies and found 95% of heatwaves were made more likely or worse by climate change. For droughts, 65% were definitely affected by our hotter world, while the figure for floods was 57%. It is now undeniable that global heating is causing more extreme weather.

The city could also receive more rainfall over a three-day period than it has has at any point in the past three and a half years, with 40mm to 90mm forecast for Saturday and another 40mm to 80mm expected on Sunday.

“The last three-day event when we saw rainfall totals potentially this high was 226mm and that was in June 2016,” Dean Sgarbossa, a senior meteorologist, said.

The heavy falls are due to a trough that is making its way from southeast Queensland and northern NSW down the NSW coastline.

Within the trough there are smaller low pressure centres that are leading to intense rainfall over some areas. The BoM said the small scale of these low pressure centres was making precise forecasting of rainfall levels in some areas difficult.

The heavy falls are expected to move into fire-affected parts of the NSW south coast over the weekend. There could also be significant falls in areas with active fires near the ACT and in Victoria’s East Gippsland region.

But those heavy falls come with warnings of water contamination from ash and silt.

Increased run-off could also lead to flash flooding and land slips, which may block access trails and roads in some areas.

WaterNSW has been monitoring areas around the Warragamba Dam, the source of 80% of untreated supply for greater Sydney.

Two silt curtains designed to trap material that could pose a risk to water quality have been in place since January.

Brogo dam, on the south coast, which supplies Bermagui, is also close to a fire ground.

On Friday, the flooding led to road closures in some areas, including several in Sydney.

In the northern rivers region, a car was washed off the road and two people had to be rescued from a caravan due to rising floodwaters.

The road to the Jenolan Caves, south-west of Katoomba, was also closed due to fears the heavy rain could cause landslides.

Does climate change cause bushfires?

The link between rising greenhouse gas emissions and increased bushfire risk is complex but, according to major science agencies, clear. Climate change does not create bushfires, but it can and does make them worse. A number of factors contribute to bushfire risk, including temperature, fuel load, dryness, wind speed and humidity. 

What other effects do carbon emissions have?

Dry fuel load – the amount of forest and scrub available to burn – has been linked to rising emissions. Under the right conditions, carbon dioxide acts as a kind of fertiliser that increases plant growth. 

So is climate change making everything dryer?

Dryness is more complicated. Complex computer models have not found a consistent climate change signal linked to rising CO2 in the decline in rain that has produced the current eastern Australian drought. But higher temperatures accelerate evaporation. They also extend the growing season for vegetation in many regions, leading to greater transpiration (the process by which water is drawn from the soil and evaporated from plant leaves and flowers). The result is that soils, vegetation and the air may be drier than they would have been with the same amount of rainfall in the past.

What do recent weather patterns show?

The year coming into the 2019-20 summer has been unusually warm and dry for large parts of Australia. Above average temperatures now occur most years and 2019 has been the fifth driest start to the year on record, and the driest since 1970.

Is arson a factor in this year’s extreme bushfires?

Not a significant one. Two pieces of disinformation, that an “arson emergency”, rather than climate change, is behind the bushfires, and that “greenies” are preventing firefighters from reducing fuel loads in the Australian bush have spread across social media. They have found their way into major news outlets, the mouths of government MPs, and across the globe to Donald Trump Jr and prominent right-wing conspiracy theorists.

NSW’s Rural Fire Service has said the major cause of ignition during the crisis has been dry lightning. Victoria police say they do not believe arson had a role in any of the destructive fires this summer. The RFS has also contradicted claims that environmentalists have been holding up hazard reduction work.

Photograph: Regi Varghese/AAP

The RFS said there were still some areas west of the ranges around Canberra, where a number of fires were burning and yet to see rainfall.

Crews were back-burning where possible, but very heavy rain could make that difficult in some places.

However, Fitzsimmons said the wet weather was putting much needed moisture back into the landscape and this would help firefighting efforts, even if hot, dry weather returned.

“We’re certainly not going to have the underlying conditions of such profound moisture deficit and drought situations dominated by this massive heat event that’s been sitting there literally for months,” he said.