Even small concentrations of smoke pollution from wildfires can be harmful to human health.
Western spring snowpack has been below normal six of the past seven years, meaning less water during the traditionally dry summer months.
Warming temperatures combined with drought conditions are major factors for the increase in wildfires.
Climate change is one reason the area burned by western wildfires is increasing.
The number of large wildfires in the West is rising and climate change is playing a role.
More water is flowing this year in California from frequent storms and melting snowpack.
Western snowpack at the end of the the wet season is up this year — but that's less likely in the future.
The average number of large wildfires burning across the Western U.S. each year has tripled from the 1970s to the 2010s.