(Under Biomes Category)
MISC
"Resource" (farming/iron/stone/water) min - the minimum value of this resource (efficiency?) out of 1.0 (=100%)
fertility multi - unrelated but it seems like this affects the amount of foliage in the biome
Resources (farming/iron/stone/water)
altitude fade - change in altitude to fade resource multiplier to 0
altitude max - top altitude boundary (highest mountain seems to be around 5000)
altitude min - bottom altitude boundary (lowest point seems to be 0)
mult - resource multiplier
From experimenting, the calculation seems to work like this:
for,
altitude max > x > altitude max
x = resource min + resource mult
altitude min > x > altitude max
x = resource min + resource multi ( 1 - (altitude change / altitude fade))
In other words, the resource value is set at resource min plus resource multi inside the altitude max/min. Outside, the value fades to resource min over the altitude fade distance. Unfortunately this means that all four resources are based off of altitude and that variation is a straight line fade outside the max/min boundaries.
Hope this helps someone out, as this is the first post I know of detailing how this works.
** this is literally my first forum/modding attempt so advice / PMs welcome!
EDIT
For those wanting a quick fix mod to set all resources in that biome to 100:
"Resource" min = 1
Everything else = 0
Remember to do this for both central and desert.