Calculating area-weighted fire intensity from FATES output

[adamhb]

Hi all,
I recently outputted FATES_BURNFRAC, FATES_FIRE_INTENSITY, and FATES_FIRE_INTENSITY_BURNFRAC for a single-site simulation at a lower montane Sierra Nevada site with conifer, oak, and shrub pfts. The variable description for FATES_FIRE_INTENSITY_BURNFRAC say's that if you divide by FATES_BURNFRAC you can get the area-weighted mean fire intensity. When I do this I get fire intensities as high as 828,773,760,000 (8e11) W m-1 (8e8 kW m-1) which I'm 99% sure are unrealistically high.

Perhaps the issue is that FATES_BURNFRAC has units of s-1 and the calculation for FATES_FIRE_INTENSITY_BURNFRAC is FIRE_INTENSITY x the fractional area of the fire, which I suppose has an implicit time dimension of something other than 1 second. How long can fires burn in FATES?

Assuming a fire burns for a day in FATES (probably should be longer?), I'm thinking that area-weighted fire intensity would actually be calculated as FATES_FIRE_INTENSITY_BURNFRAC / (FATES_BURNFRAC * 86400 s day-1).

This would give more reasonable results. Max fire intensity of ~9,000 kW m-1

Does this make sense to others? Do we assume fires burn for one day or longer?
Thanks for any input!
Adam

[ckoven]

Hi @adamhb, yes you are correct. FATES_BURNFRAC used to have units of day^-1 , but now (as of #802) has units of sec^-1. But as you point out, the day^-1 to sec^-1 conversion wasn't also applied to FATES_FIRE_INTENSITY_BURNFRAC. So the variable long name is now incorrect, one needs to divide by 86400.

[adamhb]

Thanks for confirming @ckoven !

[jkshuman]

good catch @adamhb thanks for opening this.