In the Köppen classification system, a climate will be classed as semi-arid if its mean annual precipitation in millimeters is less than ten times its defined precipitation threshold, and it will be classed as a desert if its mean annual precipitation is less than five times this threshold. The precipitation threshold is twice its mean annual temperature in degrees Celsius, plus a constant to represent the distribution of its rainfall throughout the year. This constant is 0 for regions that receive 70% or more of their rainfall during the six winter (colder) months, 28 for regions that receive such a share of rainfall during the six summer months, and 14 for those in-between.