Fire historians say the need for preventive measures like clearing brush is an important realization and a hard lesson learned from the fatalities in 2013. When Yarnell burned again last year, the flames were stopped by large fuel breaks carved between the town and the wilderness that surrounds it. No one was hurt, and only a handful of structures were damaged. The work was paid for by grants funded by the Arizona Legislature for the first time, in direct response to the need to thin out vegetation.

Still, the historians say, the changes seem almost meek when compared with the shock and magnitude of the tragedy of four years ago.

In the past, each cluster of fatal wildfires led to a round of new rules for firefighters on the ground. The 10 standard firefighting orders of the 1950s warned, “Know what your fire is doing at all times.” The 18 “watch out” situations of the 1980s laid out the risks of fighting fire when instructions and assignments are not clear. A system known as L.C.E.S., for the elements of fire safety it emphasizes — lookouts, communication, escape routes and safety zones — became the focus in the 1990s, after six firefighters died in the Dude fire in Arizona.

But the deadly fire in Yarnell has not translated into practical reforms, in part because of where it took place. While most wildfires happen on federal land and are fought by federal crews, the one in Yarnell burned on state land, and the 19 firefighters who died were members of the only city-based wildfire-fighting crew in the country, the Granite Mountain Hotshots of Prescott.

“Without a stronger federal presence, there was little way to nationalize the experience,” said Stephen J. Pyne, a professor in the School of Life Sciences at Arizona State University who specializes in the history of fire.

Nonetheless, the Yarnell Hill Fire, as it is known, has made it easier to use danger as a reason to move firefighters out of the path of flames, even if it means that communities may burn.