Aridity

Arid [ Ecology - Climatology ]	Dictionary of botanic terminology - index of names
Noun: Aridity

Lacking sufficient water or rainfall;

Lacking moisture, especially applied to regions where precipitation (rain or snow) is so deficient in quantity, or occurs at such times that they are insufficient to support vegetation. Extremely dry; the driest climates on our planet, often associated with the desert vegetation type. Semi-arid refers to places that are almost as arid as the deserts. Arid is considered the opposite of humid when speaking of climates.

Compared to wetter regions the arid regions (deserts) supports very little life however often give hospitality to a wealth of specialized living organism that usually remains hidden (especially during the daylight) or grow partially underground to preserve moisture.