It is pointed out that in order to evaluate the moisture‐factor in climate, the moisture supply or the precipitation must be compared with the water‐needs or the potential evapotranspiration, The distribution of precipitation through the year never coincides with, and seldom parallels, the distribution of potential evapotranspiration. When the precipitation is in excess of the need, the surplus goes to recharge ground‐water and produce runoff. When the precipitation does not equal the need, there is a deficiency which results in drought. Data on precipitation and potential evapotranspiration are presented for sixteen stations in the United States and tropical A