Rate of Spread (ch/h)

The typical or representative rate of spread of a potential fire based on a weighted average of four percentile weather categories.

Rate of spread is the speed with which a fire moves in a horizontal direction across the landscape, usually expressed in chains per hour (ch/hr) or feet per minute (ft/min). For purposes of the CO-WRA, this measurement represents the maximum rate of spread of the fire front.

Rate of spread is a fire behavior output, which is influenced by three environmental factors - fuels, weather, and topography. Weather is by far the most dynamic variable as it changes frequently. To account for this variability, four percentile weather categories were created from historical weather observations to represent low, moderate, high, and extreme weather days for a 20-meter grid cell in Colorado.

The Characteristic Rate of Spread represents the weighted average for all four weather percentiles. While not discussed in this report, the individual percentile weather ROS outputs are available in the CO-WRA data.