As public agencies entrusted with the management of forests, change management practices to those which recognizes the role of fire in maintaining forest health and suppression is de-emphasized, the impacts of climate variability on fire management will become more pronounced. Climate variability in the southwest is often characterized by long periods of drought. The PDSI is based on the relative dryness or wetness of an area, so that areas with differing water budgets may be compared. These divisions are illustrated in the table at right. At the national scale, the southwest is most susceptible to drought events.
Drought conditions do influence the occurrence of forest fire events in the southwest.
Data collected from tree-ring analyses were used to reconstruct the PDSI and fire events. That is to say, larger fires tend to occur when the PDSI is lower. Using data from dendrochronology studies again, Figure 2 displays a fire frequency time line for the southwest. For the first 200 years, forest fires occurred frequently until the early 1900s when fire suppression was actively engaged. Those vulnerable are the people who own homes in and adjacent to forested land and the recreational users such as hikers, campers, boaters, bird-watchers and hunters.