Therefore, understanding changes in fire characteristics requires long-term records, a regional perspective, and consideration of many factors. All of these factors influencing wildfires vary greatly by region and over time, as do precipitation, wind, temperature, vegetation types, and landscape conditions. 6 In addition to climate change, other factors-land use, large-scale insect infestation, fuel availability (including invasive species such as highly flammable cheatgrass), and management practices, including fire suppression-play an important role in wildfire frequency and intensity. These trends of longer wildfire seasons and larger wildfire size are predicted to continue as more frequent and longer droughts occur. 5 Earlier spring melting and reduced snowpack (see the Snowpack indicator) result in decreased water availability during hot summer conditions, which in turn contributes to an increased wildfire risk, allowing fires to start more easily and burn hotter. and Global Temperature and Drought indicators). 4 Similarly, climate change threatens to increase the frequency, extent, and severity of fires through increased temperatures and drought (see the U.S. 2, 3 The wildfire season has lengthened in many areas due to factors including warmer springs, longer summer dry seasons, and drier soils and vegetation. Multiple studies have found that climate change has already led to an increase in wildfire season length, wildfire frequency, and burned area. Although wildfires occur naturally and play a long-term role in the health of these ecosystems, changing wildfire patterns threaten to upset the status quo. 1 These ecosystems are important resources, both environmentally and economically. Together, forests, shrubland, and grassland cover more than half of the land area in the United States. An average of 1.7 million acres burned in July of each year from 2002 to 2020. In 1984–2001, burned area peaked in August. wildfire season is occurring earlier (see Figure 6). Burned acreage in the West has increased noticeably in nearly every month of the year (see Figure 7). Fires burn more land in the western United States than in the East, and parts of the West and Southwest show the largest increase in burned acreage between the first half of the period of record in Figures 4 and 5 (1984–2001) and the second half (2002–2020). Land area burned by wildfires varies by state.Of the total area burned each year from 1984 to 2020, the proportion of burned land suffering severe damage has ranged from 5 to 23 percent (see "high" category in Figure 3).18 This shift-combined with other ongoing changes in temperature, drought, and snowmelt-may have contributed to warmer, drier conditions that have fueled wildfires in parts of the western United States. The late 1990s were a period of transition in certain climate cycles that tend to shift every few decades.The largest increases have occurred during the spring and summer months (see Figure 6). This period coincides with many of the warmest years on record nationwide (see the U.S. According to National Interagency Fire Center data, of the 10 years with the largest acreage burned, all have occurred since 2004, including the peak year in 2015 (see Figure 2).
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