aridity (n.)

1650s, "dry, parched, without moisture," from French aride "dry" (15c.) or directly from Latin aridus "dry, arid, parched," from arere "to be dry" (from PIE root *as- "to burn, glow"). The figurative sense of "uninteresting" is from 1827. Related: Aridly; aridness.

also *es-, Proto-Indo-European root meaning "to burn, glow." 

It forms all or part of: ardent; ardor; area; arid; aridity; aril; arson; ash (n.1) "powdery remains of fire;" azalea; potash; potassium.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit asah "ashes, dust;" Hittite hat- "to dry up;" Greek azein "to dry up, parch," azaleos "dry;" Latin aridus "parched, dry," ārēre "to be dry," āra "altar, hearth;" Armenian azazem "I dry up;" Old English æsce "ash," Old High German asca, Gothic azgo "ashes."