Does Wildfire Spread Faster Uphill or Downhill?

Wildfire tends to spread faster uphill than downhill because the slope allows them to be closer to the accelerants that cause the flames. When a flame is traveling uphill, the fire’s fuel is drier and more quick to ignite because wind currents tend to travel uphill and continually push the heat closer and closer to other fuel sources that will help it spread. As the uphill slope gets steeper, wildfires will move even faster. Wildfires typically spread the next quickest downhill, and they spread slowest on level ground. With a downhill slope, wildfires have more of an opportunity to spread than on level ground because embers and fuel could roll downhill.

More about wildfires:

  • About 80% of all wildfires are estimated to be the result of human error, such as from cigarettes or campfires.

  • Animals generally are not injured in wildfires because they instinctively know how to escape. In the 1998 Yosemite wildfire in California, for example, only 1% of the area's elk population was killed.

  • In rare cases, wildfires can create fire tornadoes, known as "fire whirls," that can reach speeds of 90 miles per hour (144.84 km/h).

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