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extreme weather

Attribution studies consistently find that warming has increased the frequency of extreme fire weather days in the Mediterranean basin, while being far more cautious about any individual fire. That distinction is worth holding onto. Climate change does not light fires. It lengthens the window during which a fire, once lit, cannot be stopped — and that window is what the current European season has been demonstrating.

• 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.