What is the definition for climate ratio?

The climate ratio is used to describe how moist a climate is. It compares the precipitation (P) with the potential evapotranspiration (Ep) for a region. The written formula is: climate ratio = P / Ep. Within this formula P is the precipitation (in mm) or the amount of moisture available for evapotranspiration (the combined process of evaporation and plant respiration) and Ep is the potential evapotranspiration (in mm) or the amount of moisture needed for evapotranspiration. A ratio .4 or less is arid.
Updated on Tuesday, February 07 2012 at 11:19PM EST
Collection: precipitation