Incorporate the impact of O2 concentration on fuel flammability

[samsrabin]

incorporate the impact of O₂ concentration on fuel flammability to address the fire overestimation in Tibet:

(1) Add:

forc_po2 => atm2lnd_inst%forc_po2_grc, & ! Input: [real(r8) (:)]  O2 partial pressure (Pa)

(2) fire_m should be changed to:

fire_m = ((afuel*arh30+(1._r8-afuel)*arh)**1.5_r8) &
     *((1._r8-btran_col(c)/wtlf(c))**0.5_r8) &
     *min(1._r8, max(0._r8, (forc_po2(g)-15000)/2500._r8))

Originally posted by @lifang0209 in #2726 (comment)

[lifang0209]

@samsrabin @ekluzek @wwieder Sam requested a figure demonstrating the impact of the O₂ limit. The attached figure displays the spatial distribution of the annual burned area fraction. Observations (obs) represent the average of three satellite-based burned area products (GFED5s, FireCCI, and MODIS C6). Simulations show results for the new fire schemes both with and without an O₂ limit. The figure includes global burned area totals and spatial correlation coefficients (R) between observations and simulations.
As illustrated, the O₂ limit reduces the overestimation of the burned area fraction in Tibet, and improves the spatial pattern simulation performance (global spatial correlation with observations increases from 0.76 to 0.79).

[samsrabin]

Thanks, Fang! I'm assuming that's for 2001-2020 or so?

[wwieder]

Thanks, Fang.

[lifang0209]

Thanks, Fang! I'm assuming that's for 2001-2020 or so?

Hi Sam, this is for 2001-2014 and CTSM5.2 with fire scheme updates forced by CRUJRA. I'll check the CTSM5.3 outputs soon to make sure everything about the fire scheme goes correctly.