How do wildfires start? Firefighters tackle blaze raging in Portugal

Hundreds of firefighters in Portugal are battling to contain wildfires engulfing thousands of hectares of the Algarve.

Around 800 personnel attended a fire near the town of Odemira, south of Lisbon, overnight on Monday. More than 1,400 people have been forced to evacuate.

The fire began on Saturday and was driven south into the interior of the Algarve, Portugal’s main tourism region, by strong winds.

Much of the Iberian peninsula is expected to reach temperatures over 40C this week. The Met Office has issued a heat warning to British holidaymakers visiting Spain, Portugal and north Africa.

Odemira’s mayor, Helder Guerreiro, has said the situation is “critical, difficult, and complex”.

Take a look at our guide to how wildfires start and why they are getting worse.

How do wildfires start?

A fire needs fuel, oxygen and heat to get going. When the weather is hot and with drought conditions, often something as tiny as a spark from a train wheel can ignite a huge wildfire.

In other instances, fires occur naturally, lit by heat from the sun or a lightning strike.

A lot of wildfires are caused by human negligence. For example, campfires, discarded lit cigarettes, arson, failing to burn debris properly, and playing with matches or fireworks can all be to blame.

Once started, a wildfire can spread, thanks to wind, because of fuel – which could be dry foliage, grass or trees – or being on a slope.

In dry weather, fires are much more difficult to control and put out. Firefighters often refer to the fire triangle when trying to extinguish a blaze.

If you take away oxygen, heat or fuel, then the fire will not be able to sustain itself.

Are wildfires getting worse?

A report by the UN Environment Programme published last year forecast a global increase in “extreme fires” of up to 14 per cent by 2030, and 50 per cent by the end of the century.

Experts say the most likely cause for the trend is an average increase in global temperature, which leads to extreme drought and extreme flooding.

The authors of a recent paper in Reviews of Geophysics said in some high-latitude forest areas wildfires had increased by 50 per cent or more, even though they had already been affected by fire from 2000 to 2020.

They said that climate change is making soil dryer, which makes fires more likely and more severe when they do occur. But the impacts of this differ by region, and wildfires can be influenced by other factors.

Nasa scientists said wildfires across the world are getting worse, with a clear increase in size, number and intensity.