Fire Climate Regions Index
The fire weather occurring on a particular day is a dominant factor in the fire potential on that day. Fire climate, which may be thought of as the synthesis of daily fire weather over a long period of time, is a dominant factor in fire-control planning. In a broad sense, climate is the major factor in determining the amount and kind of vegetation growing in an area, and this vegetation makes up the fuels available for wildland fires.
The areas of North America in which wildland fires are a problem have a wide variety of fire climates. Latitude alone accounts for major changes from south to north. The shape of the continent, its topography, its location with respect to adjacent oceans, and the hemispheric air circulation patterns also contribute to the diversity of climatic types by affecting general temperature and precipitation patterns. In general, the fire season in the western and northern regions of the continent occurs in the summertime. But the fire season becomes longer as one goes from north to south, becoming nearly a year-round season in the Southwest and southern California. In the East, the fire season peaks in the spring and fall. Some fires occur during the summer months, and in the Southern States they can occur in winter also.
Because of the nature of the effects of various weather elements on fire behavior, simple averages of the weather elements are of little control value. Also, fire climate cannot be described by considering the weather elements individually. Fire potential responds to the combined effects of all of the fire-weather elements. For example, it makes considerable difference in fire climate whether or not precipitation is concentrated in the warm season or the cold season of the year. If it is concentrated in the cold season, and the warm season is dry, the fire potential during the warm season may be extreme. Where the reverse is true, the warm season may have little fire potential, while the most critical periods may be in spring and fall. Strong winds are very important in fire behavior, providing they occur in dry weather. A region may often have strong winds, but if they occur with precipitation, they are of much less importance to the fire climate.
Climatic differences create important variations in the nature of fire problems among localities and among regions-- seasonally and between one year and another. Knowledge of the similarities, differences, and interrelationships between regional weather patterns becomes a useful daily fire-control management device. A weather pattern that is significant to fire behavior in one region may be unimportant in another. What is unusual in one region may be commonplace in another. On the other hand, many large-scale weather patterns ignore regional boundaries, and one originating in or penetrating a region may then be a forewarning of what is soon likely to happen in neighboring regions. Fire-danger rating is an integration of weather elements and other factors affecting fire potential. Daily fire-danger rating is dependent on current fire weather, while seasonal and average fire-danger ratings are dependent on the fire climate. In many systems, only the weather elements are considered, because they are the most variable.
Encyclopedia ID: p364
