Figure Z. — Comparison of the XIOOO value with the 1000-h TL fuel moisture computed from 

 weather data recorded at Lihby, Mont. 1973. Hours of precipitation for the four sig- 

 nificant rainfall events are indicated. 



During spring greenup, the live herbaceous fuel moisture increases gradually from 

 the 1-h TL fuel moisture. A gradual greenup was built into the live fuel model at 

 the request of users in the Eastern United States who feared that the "instantaneous" 

 greenup originally proposed would not properly reflect the transition from high fire 

 danger in early spring to low fire danger in summer. The length of the greenup period 

 varies from 7 days for climate class 1, to 28 days for climate class 4. The length of 

 the greenup was scaled to the climate class because plants growing in drier climates 

 typically respond quicker to favorable growing conditions than do plants in wetter 

 climates . 



When a spring flush of growth becomes generally apparent, the user specifies the 

 beginning of greenup. Then the herbaceous fuel moisture is calculated according to 

 the equation: 



FMl + [(HERBGA + HERBGB * XIOOO) - FMl] * GREN 



climate dependent intercept and slope for annuals 

 or perennials from table .3 



XIOOO value 



fraction of the greenup period that has elapsed, 

 moisture content of the 1-h TL fuel. 



HFM = 



where: HERBGA, 

 HERBGB 



XIOOO 

 GREN 

 FMl 



8 



