Hello
I'm very confused by the methods determining the 90% of the average annual rainfall in SSS Credit 6.2 LEED guide.
In p103 of LEED guide, they said "For this credit, managing 90% of the average annual rainfall is equivalent to treating the runoff from the amounts listed in Table:
Watershed Rainfall per 24 Hours(ins)
Humid 1
Semiarid 0.75
Arid 0.5
I wondered Why the 90% of average rainfall is equivalent to treating the runoff of 1,0.75 and 0.5 (this is the quantity of 24 hours? not entire year?).

Thanks