What environmental factor can slow the spread of wildfires?

High humidity is a significant environmental factor that can slow the spread of wildfires. When humidity levels are high, moisture content in the air increases, which can saturate the vegetation and make it less likely to ignite. This moist environment reduces the likelihood of fire spreading rapidly because the fuel (in this case, vegetation) is less dry and more resistant to catching fire.

In contrast, low temperatures can also affect fire behavior by slowing chemical reactions; however, high humidity plays a more immediate and direct role in making it difficult for fires to develop and spread in the presence of sufficient fuel. Dense vegetation may actually contribute to the quick spread of wildfires as it provides ample fuel for the flames. Dry soil can lead to drier vegetation, increasing flammability and making it easier for fires to ignite and spread. Thus, high humidity is key in slowing wildfires by creating conditions that are less favorable for combustion.