Paramedics and firefighters are braced for emergencies across the country this week after UK forecasters predicted a fourth heatwave of the year.

Temperatures are forecast to reach as high as 35C by Wednesday, triggering heat health alerts and an appeal from fire chiefs to take care in parched parks and rural areas.

July has been 3C above average across the UK, according to provisional Met Office data, and with more than a month of summer left, the UK has already faced more days above 30C than ever before.

Southern England has had just 1% of its average July rainfall, while England as a whole has had 5% and the UK 20%, according to the Met Office.

Forecasters predict this latest heatwave will at least be shortlived. Temperatures are expected to rise from Tuesday, reaching 30C as a high pressure system sits across the east and south-east of the country, before the peak of the heat comes on Wednesday.

Scorched woodland in the Cairngorms in Scotland after a wildfire at the weekend. Photograph: Robyn Vinter/The Guardian

Temperatures would begin to gradually cool from Thursday, the Met Office said, except in the south-east where another hot day could keep the region in official heatwave conditions.

The heat was likely to have a significant impact on the health of vulnerable people and increase demand on health services, the UK Health Security Agency said on Monday, as it issued amber heat health alerts for the east and south-east of England.

They begin on Wednesday at 9am and end on Thursday. Yellow heat health alerts will remain in place for Yorkshire and the Humber, West Midlands and south-west regions for the same time period.

Ambulance and emergency medical teams anticipate a surge in patients suffering dehydration, heat exhaustion and heatstroke, as well as from patients with heart and respiratory illnesses that can be badly exacerbated by high temperatures.

“Recent episodes of extreme heat have shown how quickly patients can become seriously unwell,” said Helen Vine, the assistant director of the Association of Ambulance Chief Executives (AACE).

“With amber heat health alerts in place, we would urge people to take the risks seriously by staying hydrated, avoiding strenuous activity during the hottest parts of the day, limiting alcohol consumption and seeking advice from NHS 111 for non-emergency health concerns.”

With wildfires across Europe displacing hundreds of thousands of people in France and Spain in recent days, UK fire chiefs were also priming themselves for the possibility that the latest heatwave could increase the chance of further wildfires in the UK.

Residents of Nethy Bridge in Scotland had to be evacuated at the weekend after a large fire broke out in the Cairngorms national park. And at the height of the third heatwave in mid-July, firefighters were battling 19 significant wildfires simultaneously in England and Wales.

On Monday a spokesperson for the National Fire Chiefs Council urged the public to avoid using disposable barbecues in parks, the countryside and other green spaces, and to take care with cigarette butts. “It only takes one spark to start a wildfire, and what may appear to be a small fire can quickly escalate, threatening communities, wildlife, natural habitats and the firefighters tackling the incident.”

Human-caused climate breakdown is making every heatwave in the world more intense and more likely to happen. The sustained increase in temperatures may lead to a redefinition of the criteria for a heatwave. Heatwave thresholds for some counties were nudged up by a degree four or five years ago, said the senior Met Office meteorologist Marco Petagna.

“Going forward they’ll need to be adjusted to take into account … current climate, otherwise we’re going to more frequently go into heatwaves. It’s a moveable thing, really, as we go through a warming world.”