What the 30-30-30 rule is and why it signals extreme wildfire risk

What the 30-30-30 rule is

The 30-30-30 rule is a reference meteorological threshold used across the forestry sector: temperatures above 30 °C, wind gusts over 30 km/h, and relative humidity below 30 %. When these three conditions coincide at the same place and time, the terrain is in the atmospheric scenario most favourable for a major wildfire to spread out of control.

Why these three variables together are so decisive

Each variable is a risk factor on its own. Together, they reinforce one another: heat dries fine vegetation even further, wind supplies the oxygen that feeds the flame front and drives it forward at speed, and low humidity means any spark ignites the available fuel almost instantly. That combination is exactly what can turn a controllable outbreak into an uncontrollable front within minutes.

The limit of the analogue rule

For decades, the 30-30-30 rule has served operational centres as a general warning signal: once those three thresholds are crossed, the risk is known to be extreme across an entire district or province. What the rule doesn't say, applied in its traditional form, is where within that territory the risk is highest at any given moment, or how it combines with the actual state of vegetation in each municipality.

How technology adds precision to the threshold

A predictive monitoring platform cross-references real-time weather data with fine-fuel models at municipal level, turning a generic extreme-risk alert into a map of specific higher-exposure zones. That granularity is what lets emergency services position resources before the risk materialises, instead of waiting for the threshold to be met uniformly across the whole territory.

Graphics from Osprean's #ElTiempoEsHectáreas campaign on the 30-30-30 rule.