Trewartha’s climatic classification tends to emphasize only two principal climatic elements, especially temperature and precipitation.
Besides these, the effects of land and water surfaces on the climate of an area have also been taken into consideration. In addition to letter combinations, Trewrtha also makes use of words or phrases to designate the main climatic types.
In this classification scheme there is little provision for mathematical determination of climatic boundaries.
However, the primary objective of this classification is to divide the world into climatic regions so as to provide a framework for the study of the pattern of land use and human settlement as well as organized geographical description.
Undoubtedly, Trewartha’s system is in no way a rational classification which involves a lot of mathematical computation. Because of its simplicity and usefulness this classification is widely used by geographers.
The boundaries of the climatic regions in this classification are based on the average of the climatic conditions over a 30-year period. Lastly, this climatic classification has been kept quite simple and recognizes only a limited number of principal climatic types, usually fewer than 15.
Trewrtha is of the opinion that if the number of climatic types is increased, the basic characteristics of the climatic pattern will be obscured with the result that it will be difficult to memorize the climatic types and their distributions. In Trewartha’s classification the needs of geographers have been kept paramount.