Fuel: The type of fuel that’s helping the wildfire grow plays a unique role. For example, tree needles, brush, dead leaves, and dry grass are all very fast-burning fuels, whereas large stumps and branches are more slow-burning fuels. In drought years, this underbrush is especially dry and literally adds more fuel to the fire. That’s why those fires tend to be worse. Topography: The lay of the land plays an important role in the spread, too. Specific categories include the slope of the ground (fires tend to move fast uphill), the direction the land faces (e.g. towards the sun), and terrain (controlling wind flow). Weather: This is one of the most important factors to consider regarding how a wildfire will spread. Temperature, humidity, and wind are the most influential components. High temperatures, strong winds, and low humidity all make it easier for a fire to spread. On the topic of weather, it’s important to note the relationship between climate change and wildfires. Climate change plays a key role in increasing the likelihood of a wildfire starting and spreading. This is especially true in the Western US. Wildfires thrive in low-humidity environments, and climate change has been known to dry out the fuel that accelerates the fires. As a result: The number of large fires in the Western US between 1984-2015 has already doubled in recent years, and 75% of California’s most destructive wildfires in history have happened since 2015. For a large portion of the Western US, projections show that a global annual temperature increase of 1°C may increase the burn area of wildfires by as much as 600%. And in the Southeastern US, where lightning-ignited wildfires are common, the length of fire seasons is predicted to increase by 30% by 2060.