Fuel
Grass-shrub fuels are the most extensive fuel type in Pima County, covering nearly half of the county’s landscape. These fuels are widespread across open rangelands and valleys, creating highly flammable conditions, especially during dry and windy periods. Shrubland fuels are concentrated in foothills and canyons, while timber fuels are found in isolated "Sky Island" mountain ranges. Invasive, fire-adapted species such as buffelgrass and cheatgrass have increased fuel loads and connectivity, which heightens wildfire risk across all regimes. Urban and developed areas account for about 5 percent of the county. These areas act as barriers to wildland fire spread but remain vulnerable where they border natural fuels.
×Weather
Pima County experiences extreme heat from May through September, with summer temperatures often exceeding 105°F. Most annual precipitation occurs during the monsoon season from June through September, averaging 6 to 13 inches per year. Monsoon storms can bring intense rainfall and frequent lightning ignitions. Winter brings cooler temperatures, sometimes down to 25°F, and occasional snowfall at higher elevations. Outside the monsoon season, wildfire risk increases due to drier conditions and the buildup of fine fuels. Seasonal climate variability drives vegetation growth, fuel loading, and fire behavior. ×
Topography
Pima County’s elevation ranges from 1,200 feet to more than 9,000 feet. The landscape includes vast deserts and isolated mountain ranges known as Sky Islands, such as the Santa Catalina, Rincon, and Santa Rita mountains. The varied topography influences local climate and fire behavior. Fires can spread rapidly on steep slopes and through canyons, especially during extreme weather events. Northern and western aspects tend to be cooler and wetter, which supports denser vegetation. In contrast, southern and eastern aspects are hotter, drier, and more fire-prone. Rugged terrain and limited access can complicate wildfire response, which may allow fires to grow large in remote areas. ×
Fire Behavior
Pima County’s fire regimes are defined by wildfire intensity, frequency, seasonality, and spatial patterns, all closely tied to diverse vegetation communities. The county includes five fire regime classes (I through V), with intervals ranging from frequent, low-severity fires in high-elevation forests (6 to 30 years) to infrequent, mixed-severity fires in Sonoran Desert scrub (100 to 1,000 years). Restoration and fuels treatment planning depend on understanding these regimes, which are shaped by the landscape’s topography and vegetation. The county’s vegetation ranges from low-elevation desert grasslands to high-elevation conifer forests.
×