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The Fire Environment Wildfire behavior is governed by terrain, vegetation (fuels), and weather. Within the WUI areas in the city, the fire environment can be broadly summarized into two types: the WUI on the west side and the WUI on the south side. A different make-up of terrain and vegetation characterizes each area. Both areas experience similar weather conditions regarding temperature and relative humidity, but each area has unique wind patterns. Terrain Terrain influences wildfire in two ways. First, fires burning uphill on a slope have higher rates of spread and higher intensities because the slope brings the flames closer to vegetation above it, preheating them and allowing them to ignite more readily. Second, the aspect influences how much sun exposure is received. South and west aspects receive the greatest exposure, which makes them the hottest and driest slopes and, therefore, the most readily available to burn. A singular, long east-facing slope from Foothill Road to Pleasanton Ridge characterizes the WUI areas' terrain along the City's west side. There is some minor variation in the slope aspect where the hillside contains numerous drainages. There is an approximately 1,200-foot difference in elevation between Foothill Road and the ridge. Slopes average between 25% and 65% along the upper 1/3rd of the slope (Google Earth, 2024). Numerous hills characterize the terrain in the WUI areas along the city's south side. These hillsides are generally composed of north-south running ridgelines (closer to I-680) or east-west running ridgelines (closer to State Route 84), representing all aspects in this WUI area. These hills are considerably shorter than the Pleasanton Ridge, with only a 200 to 300-foot difference between the ridgeline and the adjacent valley. Slopes are similar, averaging about 25% with a maximum of 65% (Google Earth, 2024). Weather The City of Pleasanton’s fire season occurs when vegetation and weather conditions are conducive to the spread of a wildfire. Fire season typically begins in May when grasses and annual plants have cured and ends in October with the arrival of significant precipitation. The actual beginning and end of fire season can vary from year to year. The beginning of the fire season is dependent on how much precipitation occurs during the winter and spring and when the last wetting rain occurs. The end of the fire season is dependent on when the first wetting rains of the fall arrive. Precipitation is generally absent during fire season. The hottest and driest conditions occur July through September with a mean maximum temperature over 80°F and mean minimum relative humidities below 10%. Winds are predominantly out of the west and west-northwest (WRCC 2024). Wind speeds vary depending on the location in the City. The WUI areas on the City's west and south sides experience pronounced diurnal winds during the fire season. On the city's west side, particularly in the hillsides below Pleasanton Ridge, a significant increase in wind speeds can occur in the late afternoon and persist until after sunset. On the south side of the city, winds are primarily from the southwest, and there is typically an increase in wind speeds in the early afternoon that persists until after sunset (Altamont and Las Trampas RAWS, 2024.) Vegetation Overview of Vegetation Within the WUI Vegetation is the fuel of the wildfire. Three vegetation factors influence fire behavior. First is the volume of vegetation; volume influences how much fuel is available for the wildfire, influencing the maximum intensity and duration of the burn. Second is the arrangement of vegetation; the arrangement of the vegetation influences fire intensity as well since taller vegetation can produce greater flame lengths and a higher intensity. The arrangement 9