How do wildfires start? The natural and artificial causes of wildfires.

The Maui wildfires have taken the lives of 111 people and counting and has caused billions of dollars worth of damage to the historic city of Lahaina. Authorities call this tragedy the worst natural disaster in Hawaii’s history.

“We have suffered a terrible disaster in the form of a wildfire that has spread widely as a result of hurricane-force winds in the region and underlying drought conditions. Maui and the Big Island both experienced significant fires. Much of Lāhainā on Maui has been destroyed and hundreds of local families have been displaced,” said Hawaii Governor Josh Green in a statement.

Although there is no official statement yet on how the wildfires started, there are common ways wildfires ignite based on patterns found in other wildfires that have occurred in the United States.

Wildfire season in the mainland United States quickly approaches as the summer season comes to a close. How do wildfires start? Luca Carmignani, a Fire Advisor from the University of California Agriculture and Natural Resources, says there are several ways wildfires may start.

Here is some information about how wildfires often start, and what you should know about them to stay safe.

What is the definition of a wildfire?

A wildfire is an uncontrolled fire that occurs on open land with vegetation, Carmingnani said.

What causes wildfires?

Wildfires can start by both natural and artificial ignition. Natural ignitions occur within nature and without the influence of humans or machinery. Artificial ignition is a fire started by machinery, cars or human-made.

Lightning is the most common natural cause of wildfires. In higher elevations, lightning sometimes touches dry vegetation, which sparks a fire that can easily become uncontrolled. This spark, combined with dry winds can escalate a fire to uncontrollable states.

Artificial ignition is any source of a wildfire started by something other than a natural cause. One very common source is caused by roadside ignition, Carmignani said. In cities with roads placed by wildlife, like Southern California, it is very common for vehicles to unknowingly ignite a fire.

“For example, you have a truck with a train that drags on the road and generates sparks,” Carmignani said. “Or you have like a catalytic converter, there are different ways that cars and trucks can start a fire from the road.”

Another example of artificial ignition is a piece of machinery hitting a rock that generates a small spark that catches on to dry vegetation nearby. This is very common during dry months like September when the air is especially dry.

In some places, the force of strong winds will cause power lines to move and, depending on the type of system may generate sparks that eventually land on dry fuel like grass or vegetation, Carmignani said.

Carmignani also says unextinguished campfires are a prevalent human cause of wildfires.

“Some people (go) camping, (and) sometimes they don't put out the campfire,” Carmignani said. “And it can smolder for days and eventually, when something gets moved, the smoldering goes back to flaming and that starts a fire.”

When is wildfire season?

Historically, wildfire season typically begins in July and ends around late November to early December, Carmignani said. This time of year has the driest conditions which are perfect for igniting and burning vegetation.

“You have these drier months where you don't have a lot of rain, all of the grass and small vegetation that grew in the spring gets drier so it's easier to ignite and burn,” Carmignani said. “Also for example in a lot of parts of the states, those are months where you have strong winds.”

Carmignani says that these conditions greatly influence fire behavior during this time of year.

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Are wildfires natural?

Yes. Fires are part of the natural ecosystem of the earth, Carmingnani said. In many regions of the United States, wildfires are a natural part of maintaining the natural ecosystem.

While many may blame climate change for an increase of wildfires, that is not entirely true. “Climate change is a factor in determining the behavior of a fire, but it’s not responsible (for) wildfires,” Carmingnani said. Global warming affects the state of vegetation in nature which contributes to the severity of fires but the occurrence of fires themselves is completely normal.

In fact, some fire-prone areas in the United States utilize a controlled method of fire to help ease the damage of wildfires during peak seasons. These prescribed fires also eliminate invasive species, reduce hazardous fuels and promote vegetation regrowth.

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This article originally appeared on USA TODAY: What causes wildfires? How they start, other facts.