1. In W. Köppen's 1918 climatic classification, the major category (B climates), which includes steppe climate and desert climate. These climates, unlike the others in his work, are defined strictly by the amount of annual precipitation as a function of seasonal distribution and of annual temperature (see formulas under steppe climate). In contrast are the rainy climates. 2. In C. W. Thornthwaite's 1948 climatic classification, any climate type in which the seasonal water surplus does not counteract seasonal water deficiency; thus it has a moisture index of less than zero. These types include the dry subhumid, semiarid, and arid climates. In contrast are the moist climates. The dry climates are subdivided further according to values of humidity index into the following: little or no water surplus; moderate winter water surplus; moderate summer water surplus; large winter water surplus; large summer water surplus.