Human activity and climate change both play important roles in causing wildfires in California, according to a study published last Thursday.

The study — co-authored by UC Berkeley wildfire specialist Max Moritz and campus professor of agricultural and resource economics and policy Peter Berck — concluded that in many areas of California, human activity accounts for about half of the total wildfire count. The study also found that failure to include human activity in future fire estimates could significantly overstate the correlation between wildfires and climatic change.

“We don’t have long levers on climate change, but when it comes to local development, that’s a place where we do have a long lever,” said Michael Mann, co-author of the study and assistant professor of geography at George Washington University. “People need to look closely at how their decisions affect not only themselves but also their neighbors.”

According to the study — conducted by a group of researchers from UC Berkeley, George Washington University and the U.S. Geological Survey, among others — humans are currently responsible for igniting approximately 95 percent of wildfires in California. The study also found that California and the U.S. Forest Service reported spending more than $5 billion on wildfire suppression in the state between 1999 and 2011.

The study examined fire patterns in California through state fire parameters and climate data, and it used California census data to model the extent of human activity — namely human settlements — and housing density throughout the state.

Researchers then used this data to develop a regression model — a graph used to describe correlation between two variables — to estimate fire counts and burned areas for the period of years between 1951 and 2050. Analysis of data found that the inclusion of humans as influencers of wildfires made predictions of wildfires more accurate.

Housing density also proved to be an important factor in influencing wildfires, according to Mann. Mann said that fires are more likely to spread in public spaces and housing areas with higher housing density up to a point where high-density neighborhoods’ increased levels of fire suppression and lack of combustible materials make fires less frequent.

According to Bill Stewart, a forestry specialist at UC Berkeley, areas with low-density housing have a higher risk of fire because it is more difficult for owners of larger properties to irrigate their lands.

Mann said the Berkeley Hills area could be considered a dangerous area for wildfires because of its dry conditions and low-density housing. Mann added that improving private and public land use practices and fire management practices can lower the risks of fires.

But Stewart said the area within and surrounding Berkeley has not had a significant wildfire since the Oakland fires of 1991.

“We’ve had a fair number of fires in Oakland and Fremont, but most of them have been on grasslands,” Stewart said. “Once a fire gets going and it has vegetation, it can burn for a while.”