There are two variations of a desert climate: a hot desert climate ("BWh"), and a cold desert climate ("BWk"). To delineate "hot desert climates" from "cold desert climates", there are three widely used isotherms: most commonly a mean annual temperature of , or sometimes a mean temperature of in the coldest month, so that a location with a "BW" type climate with the appropriate temperature above whichever isotherm is being used is classified as "hot arid" ("BWh"), and a location with the appropriate temperature below the given isotherm is classified as "cold arid" ("BWk").