Useful notes on Trewartha’s Classification of Climate

Glenn T. Trewartha is one of the eminent American climatologists who have produced several modifications of the Koppen Classification since the mid-1930s. In his book ‘An Introduction to Climate’ (1980) his latest revision differs radically from the Koppen’s classification.

The climate classification system devised by Trewartha represents a compromise between purely empirical and genetic methods. Besides being simple and explanatory, it combines the basic fundamentals of the empirical as well as the genetic classification schemes.

Trewartha, while proposing his climatic classification was conscious of the fact that the classification systems of Koppen and Thornthwaite being based on certain statistical parameters of certain weather elements were cumbersome and complex.

The empirical- quantitative classification systems as devised by these authors produced such a large number of climatic types and subtypes using different criteria that it was rather too difficult to easily remember them.

Keeping this aspect in view, Trewartha recognized only a limited number of principal climatic types, usually fewer than 15. However, if required, he was in favour of adding numerous second-and third-order sub-divisions within a climatic type or region as the case may be.

The aims and objectives of Trewartha’s climatic classification are very clear. In his opinion, “people such as geographers, biologists, or agriculturists.

Who need to understand and use the climatic environment for their own purpose, should have the facts of climate presented realistically, not forced into a preconceived genetic structure or scheme of type location.

First and foremost, they must be guided by the observed data. “In this way he is more in favour of empirical method of climatic classification. From the utilitarian point of view, he considers such a type of classification as superior to genetic classification of climate.

However, at the same time he also recognizes the merits of the genetic type of climatic classification. According to him, “genesis not only increases interest and adds to the scientific quality of climatic analysis, but also gives an extra-dimension of insight to the students’ understanding of the description.”

He was convinced that as far as possible genetic classification must supplement the empirical classification of climates. The following climatic classification as proposed by Trewartha is a highly modified form of the most widely accepted classification scheme of Koppen.

Like may other climatic classifications, Trewartha also made use of the two most important and basic weather elements, i.e., temperature and precipitation as the basis for his own classification.

Trewartha has classified world climates in 6 great climatic groups out of which five (A, C, D, E, F) are based on temperature criteria, and the sixth (B) is the dry group based on precipitation.