By Laura Zuckerman

SALMON, Idaho (Reuters) - U.S. researchers have developed a first-of-its-kind numerical scale to measure wildfire risks to property and communities in the wake of a fire season ranked the third most extensive since 1960, government officials said on Thursday.

The index, devised as an ascending scale from 1 to 4, will rate the vulnerability of homes or other structures to wildfires according to such factors as climate, surrounding terrain, and the types of vegetation that could fuel a fire, as well as building design and materials.

The scale was designed to help fire managers better allocate firefighting resources according to potential property losses, rather than based on only the size and scope of a fire, and for greater advanced planning to mitigate wildfire hazards.

Each ranking will actually be assigned as two separate numbers - one gauging a structure's vulnerability to direct fire exposure and one measuring the potential risk from blowing embers.

"You could have a vulnerability to one and not the other," said Alex Maranghides, fire protection engineer with the National Institute of Standards and Technology. "But structures could be hardened to protect against both kinds of threats."

The wildfire index differs from numerical scales used to rate other natural disasters, such as earthquakes or hurricanes, which are essentially measured according to their own inherent strength.

It is geared toward communities with the greatest exposure to wildfires, those lying in the so-called wildland-urban interface - particularly in the Western and Southern states where forests and grasslands most often meet towns and resorts.

Maranghides, who developed the system with a U.S. Forest Service researcher, said results from planned field testing in Texas and California will be available in the coming months.

The scale is designed to be applied to buildings before the outbreak of a wildland blaze but can also be employed to previously unrated property in the event of fire.

Predicting threats posed by wildfires is unlike assessing natural disasters such as floods because risk levels rapidly fluctuate over shorter distances, Maranghides said. Continued...