After the deadliest start to a year in Philadelphia since 2012, police say that nearly 90 percent of the killings in the city since January have been committed with guns, a proportion that Commissioner Richard Ross said Tuesday is “alarming.”

Speaking at a news conference at Police Headquarters, Ross said that 89.5 percent of the city’s 131 homicides this year have involved a firearm — about 5 percent higher than the typical share in recent years, and significantly higher than the 1990s, when the city routinely recorded more than 400 homicides annually.

“It’s concerning to us for a lot of reasons,” Ross said.

The announcement came as Ross said he was planning to change hours or assignments for “dozens” of officers this summer to put more cops on the street, a maneuver he hopes will help prevent shootings or other criminal activity as the weather warms up and more people spend time outside.

Although he offered few specifics on the staffing changes, Ross cited last August, when police statistics show more than 150 people were shot. He said that the deployment shifts — which he described as larger than usual — were being implemented “to get in front of that as best [as] we can.”

He said some administrative staff would be assigned patrol shifts, while other officers would be asked to work extra hours at different times of the day.

“That is problematic for us, the number of firearms that are being used to commit murder in this city,” Ross said.

The share of homicides committed by firearm in the city has been gradually rising. In 1988, police statistics show, 53 percent of the city’s murders were committed by a firearm, and that percentage remained at or below 80 percent from 1989 to 1995.

Since then, the statistics show, the percentage of homicides committed by gun each year dipped below 80 percent just twice.

Ross did not offer reasons for the apparent shift. But the percentage of homicides committed with guns has been increasing nationally: According to the Centers for Disease Control and Prevention, about 75 percent of U.S. homicides in 2016 were committed with a firearm. The Washington Post said that figure was the greatest share of homicides by gun in the federal record.

Ross said that the increasing use of guns in killings in Philadelphia has come even as police this year have nearly doubled the number of gun-related arrests compared to the same date in 2015.

Through Monday, the city had recorded 131 total homicides, the most through May 27 since 2012, when 140 were slain.

The uptick comes after the city recorded 350 killings in 2018, the highest year-end total in more than a decade. Ross and other officials, including District Attorney Larry Krasner, attributed at least some of that increase to a higher percentage of drug-related murders.

In January, Mayor Kenney unveiled a plan aimed at reducing the city’s level of gun violence, with a sprawling set of recommendations that included job training, using so-called crisis intervention teams in violence-plagued neighborhoods, and clearing blight.

Ross said the Police Department also has begun pushing programs aimed at helping community members find jobs or get high school diplomas, among other initiatives, which he hopes will support the department’s more traditional crime-fighting tactics.