Catastrophic fire danger conditions have been declared for much of South Australia for Wednesday, with more than 100 schools closed and at-risk residents told to leave their homes.

The Bureau of Meteorology has forecast a maximum 42C for Adelaide, while the mercury is expected to reach 45C at Murray Bridge, 44C at Renmark, Port Augusta, Port Lincoln and Whyalla, and 43C at Port Pirie.

Seven districts were declared catastrophic fire danger zones on Wednesday – including the Mount Lofty Ranges and mid-north near Adelaide – while two were rated ‘extreme’ and six ‘severe’.

In regions affected by catastrophic danger, national parks and reserves will be closed as well as schools with R1 or R2 bushfire risk ratings.

The Country Fire Service advised people living near bushland in catastrophic fire ban districts to leave late Tuesday or early Wednesday morning.

It warned a bushfire could not be controlled in such conditions.

A total fire ban will be in place across the state.

The Bureau of Meteorology acting supervising meteorologist Paul Lainio said several November heat records could fall on Wednesday.

“Wednesday’s forecast for Adelaide at this stage is 42C, just shy of West Terrace’s hottest November day in 1962 on 30 November of 42.7C,” he said.

“Across South Australia, temperatures on Wednesday will peak 8-18C above average ahead of a cold front that’s accompanied with strong winds.

“Those towns that may break temperature records are in the south and west of the state and include Victor Harbor, Nuriootpa, Keith, Naracoorte, Murray Bridge and Robe and Lameroo.”

Quick Guide Climate change and bushfires Show 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 is the evidence on rising temperatures? The Bureau of Meteorology and the CSIRO say Australia has warmed by 1C since 1910 and temperatures will increase in the future. The Intergovernmental Panel on Climate Change says it is extremely likely increased atmospheric concentrations of greenhouse gases since the mid-20th century is the main reason it is getting hotter. The Bushfire and Natural Hazards research centre says the variability of normal events sits on top of that. Warmer weather increases the number of days each year on which there is high or extreme bushfire risk. 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 SES chief of staff Graeme Wynwood urged people to drink plenty of water and to avoid the heat of the day.

“If you do need to go out, do so first thing in the morning or later in the day when it is usually much cooler,” he said.

Wynwood said older people were more prone to heat-related illnesses because their bodies may not adapt as well to change.

“One of the most critical things people can do is to consider those who are most vulnerable to the heat and making sure they are coping,” he said.

“Identify family, friends and neighbours who are elderly or frail and check on them to make sure they are OK and using their fans and air conditioners.”