Warren Thornthwaite

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Charles Warren Thornthwaite is an American geographer and climatologist who devised a climate classification system in 1948 and created a useful water budget computation of potential evapotranspiration. He was the eldest of three children growing up in a rural township of Bay County, Michigan. Before he completed his formal education, he was obligated to support other members of his family. In the fall of 1918 he entered the Central Michigan Normal School (now Central Michigan University), an opportunity provided by the Students' Army Training Corps (S.A.T.C.). He graduated in 1922.

After his graduation, Thornthwaite taught high school at Owosso, Michigan. In 1924 he resumed his studies and entered the University of California for graduate work in geography. He got married in 1925 with Denzil Slentz. In 1930 he received his second Ph.D. in geography awarded by the University of California. While at Berkeley, he spent part of his time drawing maps and experimented with map projections.

In 1927, he went to the University of Oklahoma as an instructor in geography. He had an interest in climate, and was familiar with the Köppen classification. He worked through the whole problem of defining climates and with an immense amount of labor devised his classification in 1931. The classification was awkward, but it contained two important innovations. It asserted that the relation between precipitation and evaporation, not temperature, is the most important basis for distinguishing climates. He interpolated a transitional type, subhumid, between humid and arid climates.

In 1934 he went to the University of Pennsylvania for a year's work with the Study of Population Redistribution. In 1935, following the advice of Carl Sauer, Thornthwaite formulated many of the investigations carried out in the new Soil Conservation Service.

In collaboration with Benjamin Holzman, he undertook the investigation of the flux of water vapor upward from natural surfaces. Unfortunately, it failed because of the inadequacy of the instruments available for measuring the critical metereological parameters. In 1942, Thornwaite spent some time in Mexico making the first application of his method of scheduling irrigation according to the water content of the soil. During the war time he worked in his office in Washington, D.C. In 1948, Thornthwaite published the paper "An Approach Toward a Rational Classification of Climate."

While in Washington, he established the Laboratory of Climatology and became very well known operating as C.W. Thornthwaite Associates. His substantive work brought him personal recognition, including the presidency of the Commission for Climatology of the World Metereological Organization. In 1963, a week before his death, Thornthwaite was awarded an honorary doctorate from Central Michigan University.

This contribution was written by Glenda Machado Dias based on the available online literature.