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fire weather explained

Wildfires need three things: fuel, ignition and weather that lets fire spread faster than people can stop it. Fuel changes over decades. Ignition is close to constant, since most fires in Europe start with human activity. Weather is the variable that changes week to week, and it is where the climate signal shows up most clearly.

• Dead fuel — leaf litter, fallen branches, cured grass — responds to humidity within hours. It governs how easily a fire starts and how fast it runs.
• Live fuel — shrubs and tree canopy — responds over weeks to months. It governs whether a surface fire climbs into the crown.
• When live fuel moisture drops below roughly 80 per cent of dry weight in Mediterranean shrubland, crown fire becomes plausible on almost any windy afternoon.
• Spring rainfall deficits are therefore a better predictor of a severe August than August temperatures alone.