Which fuel is the most susceptible to changes in relative humidity?

Grass is the most susceptible to changes in relative humidity due to its high surface area-to-volume ratio and its structural composition. When relative humidity levels rise, grass can absorb moisture from the air quickly, leading to an increase in its moisture content. Conversely, during dry conditions, grass can quickly lose moisture, making it drier and more flammable.

Grasslands often have a rapid response to changes in environmental conditions compared to other fuel types. This attribute makes them particularly challenging to manage during fire seasons, as the fire behavior can change rapidly with shifts in humidity. In contrast, other fuels, such as branch wood or large brush, tend to be less affected by short-term changes in humidity due to their larger moisture-holding capacity. Additionally, medium duff, which refers to decomposed organic matter, also has a slower response to humidity changes, retaining moisture for longer periods.

Understanding the moisture dynamics of grass helps firefighters anticipate fire behavior and develop appropriate strategies for fire suppression and prevention in grassland areas.