humidity index

humidity index

[hyü′mid·əd·ē ‚in‚deks] (climatology) An index of the degree of water surplus over water need at any given station; it is calculated as humidity index = 100 s/n, where s (the water surplus) is the sum of the monthly differences between precipitation and potential evapotranspiration for those months when the normal precipitation exceeds the latter, and where n (the water need) is the sum of monthly potential evapotranspiration for those months of surplus.