In parts of the southwestern U.S., the commencement of the Southwest Monsoon initiates a decrease in wildland fire occurrence. Corresponding changes in meteorological elements such as relative humidity and dew point are some of the mitigating factors. For example, one commonly used climatological definition of the monsoon is three or more consecutive days of 55°F dew point occurrence at Tucson. This may or may not be relevant to wildland fire occurrence depending on location, and other related factors, such as fire danger, may be equally important. However, quantitative threshold values between meteorological/fire danger elements and fire have not been formally identified or quantified for any variable or index. The problem becomes quite complex with interannual spatial and temporal variability in both the monsoon and fire occurrence. This year-to-year variability also creates a significant challenge for fire management decision-making and strategic planning. Thus, a determination of monsoon and fire relationships is important not only from a scientific perspective, but also the societal implications.

This study examines the monsoon and fire relationship. Historical fire occurrence data in Arizona and New Mexico, and weather and fire danger variables from Remote Automatic Weather Stations across the region are analyzed in an effort to describe and assess monsoon/fire patterns and impacts. This paper will summarize relevant findings of this research, with emphasis given to the climatology of the region, interannual variability, and the monsoon/fire relationship.