C. W. Thornthwaite

C. W. Thornthwaite

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Charles Warren Thornthwaite (March 7, 1899 - June 11, 1963) was an American geographer
A geographer is a scholar whose area of study is geography, the study of Earth's natural environment and human society.Although geographers are historically known as people who make maps, map making is actually the field of study of cartography, a subset of geography...

 and climatologist. He is best known for devising a climate classification system, published in 1948, that is still in use around the world, and also for his detailed water budget computations of potential evapotranspiration. He was Professor of Climatology at Johns Hopkins University
Johns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...

, adjunct professor at Drexel University
Drexel University
Drexel University is a private research university with the main campus located in Philadelphia, Pennsylvania, USA. It was founded in 1891 by Anthony J. Drexel, a noted financier and philanthropist. Drexel offers 70 full-time undergraduate programs and accelerated degrees...

, President of the Commission for Climatology of the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

, a recipient of the Outstanding Achievement Award of the Association of American Geographers, and the Cullum Medal from the American Geographical Society
American Geographical Society
The American Geographical Society is an organization of professional geographers, founded in 1851 in New York City. Most fellows of the society are Americans, but among them have always been a significant number of fellows from around the world...



Thornthwaite was born in Bay City, Michigan
Bay City, Michigan
Bay City is a city in the U.S. state of Michigan located near the base of the Saginaw Bay on Lake Huron. As of the 2010 census, the city's population was 34,932, and is the principal city of the Bay City Metropolitan Statistical Area, which is included in the Saginaw-Bay City-Saginaw Township North...

. He attended Central Michigan Normal School
Central Michigan University
Central Michigan University is a public research university located in Mount Pleasant in the U.S. state of Michigan...

, graduating in 1922. He taught high school for the next two years in Owosso, Michigan
Owosso, Michigan
Owosso is a city in Shiawassee County in the U.S. state of Michigan. The population was 15,713 at the 2000 census. The city is located on the eastern side of Owosso Township, but is politically independent...

, then for the next four years he was employed as a geographer for the Kentucky Geological Survey
Kentucky Geological Survey
The Kentucky Geological Survey is a department of the University of Kentucky that provides information on the geology of Kentucky.According to its website, the KGS "conducts research, collects data, and serves as the State's official archive for data on petroleum, coal, minerals, ground water, and...

. While thus employed, he also became an assistant professor in the University of Oklahoma
University of Oklahoma College of Atmospheric and Geographic Sciences
The College of Atmospheric and Geographic Sciences at the University of Oklahoma consists of the School of Meteorology and Department of Geography...

 Department of Geography, serving there from 1927 to 1934. Meanwhile, he studied geography through the auspices of the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

, a student of Carl Sauer
Carl O. Sauer
Carl Ortwin Sauer was an American geographer. Sauer was a professor of geography at the University of California at Berkeley from 1923 until becoming professor emeritus in 1957 and was instrumental in the early development of the geography graduate school at Berkeley. One of his best known works...

. He obtained his of Ph.D. in geography in 1930, successfully defending a thesis on the subject, ‘Louisville, Kentucky: a study in urban geography’, a research project which used aerial photographs, field observation, data analysis and detailed mapping to describe the urban geography of Louisville. He quickly moved away from geography to climatology, but recent scholarship suggests he was nonetheless ahead of his time in his thesis project and that many of the techniques he used would later be standard procedures.

At Central Michigan Normal School he became friends with John Leighly and later, they both studied at Berkeley, with Leighly becoming his mentor. Leighly, a professor at UC Berkeley for 62 years, would write his obituary.

In 1931 he published “The Climates of North America: According to a New Classification” and his true vocation as a climatologist was launched, a vocation that married the science of climatology with that of geography. In 1934, he left the University of Oklahoma to study internal migration within the United States (at the University of Pennsylvania
University of Pennsylvania
The University of Pennsylvania is a private, Ivy League university located in Philadelphia, Pennsylvania, United States. Penn is the fourth-oldest institution of higher education in the United States,Penn is the fourth-oldest using the founding dates claimed by each institution...

). In 1935, he was appointed chief of the climatic and physiographic research division of the US Soil Conservation Service
Natural Resources Conservation Service
The Natural Resources Conservation Service , formerly known as the Soil Conservation Service , is an agency of the United States Department of Agriculture that provides technical assistance to farmers and other private landowners and managers.Its name was changed in 1994 during the Presidency of...

. The division ceased to function in 1942, but he remained on staff of the USDA until 1946. Included in his output from this period was the USDA technical bulletin, written with Benjamin Holzman, Measurement of Evaporation from Land and Water Surfaces.

Leaving government in 1946, he opened the Laboratory of Climatology in Seabrook, New Jersey
Seabrook, New Jersey
Seabrook is an unincorporated area within Upper Deerfield Township in Cumberland County, New Jersey, United States. The area is served as United States Postal Service ZIP code 08302....

, which he operated until his passing in 1963. The facility continued to operate under the management of John Russell Mather. One of his first papers would also be his most cited: "An Approach Toward a Rational Classification of Climate" (1948). This paper would be used by scientists across North America and around the world. It incorporates evapotranspiration, temperature and precipitation information and is widely used in studying animal species diversity and potential impacts of climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...


Mather shared authorship with Thornthwaite in their 1955 monograph "The water balance", The Water Balance was Thornthwaite’s second major contribution to climatology, after Rational Classification. The water budget was a simple and easily used methodology for estimating water surpluses and runoff, and the difference between surpluses and runoff, to estimate the amount of water would recharge an aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...


He was a professor of climatology at Johns Hopkins University
Johns Hopkins University
The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...

from 1947 to 1955.

Personal life

He was married to Denzil Slentz in 1925. They had three daughters. When his wife died in 1962 he established the Charles Warren and Denzil Slentz Thornthwaite Memorial Scholarship Fund in her memory. The fund awards annual merit scholarships to students in meteorology and earth science at Central Michigan University.

Further reading

  • F. Kenneth Hare, “Obituary: Charles Warren Thornthwaite 1899-1963” Geographical Review, 53:595-597, 1963.
  • John Russell Mather and Marie Sanderson, The Genius of C.Warren Thornthwaite, Climatologist-Geographer, University of Oklahoma Press, 1996. (Synopsis)

External links