The timing of fireworks-caused wildfire ignitions during the 4th of July holiday season.

Although anthropogenic climate change is causing increased wildfire activity in the United States (US), humans are also an important ignition source. Humans cause a surge in wildfire ignitions every 4th of July (Independence Day in the US) through the use of fireworks. We examine the 4th of July peak in fireworks-caused wildfire ignitions and show that their spatial distribution varies but has been heavily concentrated in the west and north central US and predominantly on tribal lands. Further, we show that the weekly timing of the 4th of July influences both the number and weekly distribution structure of fireworks-caused ignitions. We interpret these weekly and daily-scale distribution patterns of fireworks-caused ignitions to reflect the influences of human behavioral variations, culture, and fireworks regulations. For example, our analysis suggests that weekends and religious days of rest (e.g., Saturday, Sunday) have a dampening effect on the number on wildfire ignitions due to fireworks, and that weekends and the timing of work holidays likely impact the weekly distribution of fireworks-caused ignitions. Additionally, comparisons of fireworks-caused ignitions before and after the 4th of July at the daily and weekly scale likely reflect the efficacy of firework sales regulations and human behavioral tendencies towards pre-holiday impulsiveness. Given the predictability of the fireworks-caused ignitions and rising costs of wildfire mitigation, these results have several important management and policy implications.