Fuel moisture modelling

Recent work has focused on development of new fuel moisture models for the Accessory Fuel Moisture System of the Canadian Forest Fire Danger Rating System.

Sheltered Duff Moisture Content

A model was developed to track moisture in the upper layers of the organic layer in sheltered locations within 0.75m of the boles of a mature fully stocked jack pine stand (the standard stand type for the Canadian Forest Fire Weather Index (FWI) System and it's fuel moisture models). This new moisture model (which was similar to the FWI System's Duff Moisture Code (DMC)) was developed to give operational agencies an index of moisture for sheltered areas at the based of overstory trees where lightning is expected to ignite fires.

Stand specific litter moisture

The FWI System's Fine Fuel Moisture Code (FFMC) represents moisture in the litter layer of a jack pine or lodgepole pine stand, and is used in a relative sense across the country to provide a rating of litter moisture content in a range of stand types. A historic database of litter moisture measurements (taken from small scale test fire work carried out by the Canadian Forestry Service (CFS) from 1940 to 1961) was analyzed along with onsite weather information to develop models relating the FFMC to actual litter moisture in a range of stand types (pine, spruce, aspen, mixedwood, Douglas fir), over a range of stand closures (light, moderate, dense), and across several seasons (spring, summer, fall).

In this work it was found that the relationships between FFMC and actual litter moisture also depended on the moisture in the organic layer (as represented by the DMC). A method of adjusting the FFMC based on the DMC was also developed.

Grass moisture model

The FWI System's FFMC tracks moisture in a litter layer sitting above what is generally a fairly moist organic layer in a closed canopy jack pine or lodge pole pine stand. The built in response time of this fuel layer (roughly 2/3rds of a day) reflects the influence of these stand related factors and does not account for solar radiation effects on fuel heating and moisture exchange. Litter moisture content in open fields of cured grass can change much more rapidly than is modelled current by the FFMC. In this project a new grass moisture model (similar to the FFMC) was developed. Litter in this model had a much faster response time (on the order of 1 hour) and accounts for the influence of solar radiation on drying rate.