CLIMATE AND FOREST FIRES IN NORTHERN 

 CALIFORNIA 



By S. B. S?iow, 



forest Examiner, U. S. Forest Service 



In a broad way, the general relation between climate and fire is 

 obvious. The annual recurrence of the fire season is accepted as a 

 matter of course ; but we do not yet know when, in a specified locality, 

 the potential fire season begins, or even when it ends, nor the weather 

 conditions during the fire season which create emergency periods or 

 periods of no danger. Neither is there definite information regarding 

 the relative importance of wind, slope, temperature, or humidity in de- 

 termining the rate of spread. 



The possibility of fires starting and the rate at which they will spread 

 are largely dependent on the climate, using the term in a broad sense ; 

 but any study of the relation of climate to fires, to have much value, 

 must analyze the effect of each of the several components before 

 attempting to determine the efiPect of climate as a unit. 



This paper is but a bare start, and can claim to present only a few 

 definite figures of perhaps merely local value to illustrate certain 

 specific relationships between climatic factors and forest fires. 



The data used were obtained at the Feather River Experiment Sta- 

 tion in 1915. 1916. and 1917, m connection with a study of the rate of 

 spread of fires as controlled by physical factors. 



IGNITION POINT 



Logically, the first point to be considered is the ignition point of 

 litter, or that percentage of moisture, based on dry weight, at which 

 the ground cover can catch fire and spread. 



The litter of the timber — composed of needles, small twigs, bits of 

 bark, dead weeds, and grass — holds against gravity, when saturated 

 with moisture, from 60 to 110 per cent of its dry weight. Capacity 

 seems to depend on the age, degree of decomposition, and relative 

 proportions of the various substances. Table 1 shows the results of a 

 series of tests on the saturation point. 



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