Wildfires are sparked either by natural events (generally lightning) or by human activities. But people started 87% of U.S. wildfires from 2001 to 2024, accounting for almost half of all acres ...

Table 3. Top 10 ACIS stations with the highest number of days at or above a CSI of 3 during April 2025. We analyzed 191 Applied Climate Information System (ACIS) stations associated with U.S. cities.