Amidst the heatwave: Does heat cause forest fires?

With large parts of southern Europe suffering devastating wildfires, are high temperatures responsible?

With temperatures reaching and even exceeding 40-45°C, hundreds of emergency forces have been battling numerous forest fires in southern Italy and Greece for days.

Sicily and the Aegean island of Rhodes have been particularly affected. In addition to carelessness and arson, spontaneous combustion due to the heat is repeatedly cited as the cause of the fires.

High temperatures alone do not trigger forest fires. The combination of intense heat and prolonged drought only sets the stage for fires to start more easily - especially when an ignition source is present.

Parched vegetation cannot burst into flames without human intervention. Even temperatures of 50 to 60°C are not sufficient to start a fire; they would need to be well over 100°C.

Freshly cut hay can actually self-ignite, though only if stored too densely by humans. Decomposition processes of moist hay can cause the it to heat up by more than 150°C, releasing flammable fermentation gases, which can suddenly ignite.

However, this process can even take place in cooler weather, so is not a result of hot summer air, but rather faulty storage and human negligence.

Straw must be heated to at least 250°C before it bursts into flames, while wood, depending on the residual moisture, can only catch fire between 280 and 340°C. So spontaneous combustion is out of the question.

Glass is often known to be a fire-starter, but relies on a very specific set of circumstances, including the type of glass, shape and surface properties.

The only natural cause of such fires may be ignition by lightning. However in our latitudes, thunderstorms are often accompanied by heavy downpours, so this cause is generally rare.

Ultimately, carelessness handling open fires or throwing away cigarette butts remain the likely cause of most forest and bush fires. Negligent, and in some cases even intentional arson are often the cause of such devastating fire disasters.