Thornthwaite, C. Warren (1899–1963)

Charles Warren Thornthwaite was one of the most influential climatologists of the 20th century. His work on the water balance concept remains a legacy today in environmental and scientific disciplines. Scientists used his water balance methods to depict regional climates and to solve environmental and geographical problems specifically related to agriculture and water balance. Thornthwaite realized that a more logical approach to the moisture factor in climate was needed. As a result, he developed the concept of potential evapotranspiration (PE)—evaporation and transpiration from a uniformly covered ground surface of vegetation that would be adequately supplied with water. Empirical relationships were developed to determine PE based on [Page 2822]simple measures of air temperature and a latitude factor to adjust for day length and variables either measured at numerous weather stations worldwide or determined from Earth-sun relationships. Thus, PE, expressed as a depth measure, can be directly compared with precipitation to arrive at estimates of surplus and deficits for the soil-vegetative system and in hydrology to determine runoff.

Thornthwaite had a major impact on the field of climatology through his development of a rational classification of world climates based on water balance principles and the concept of PE. His career spanned several positions, from which he crafted ingenious applied analyses and contributions: Chief of the Climatic and Physiographic Division of the Soil Conservation Service in the Department of Agriculture, a consulting climatologist for Seabrook Farms in New Jersey, and an originator of a consulting company, C. W. Thornthwaite Associates. He also established the Laboratory of Climatology in Centerton, New Jersey. Thornthwaite was elected as the first president of the World Meteorological Organization's Commission on Climatology in 1951. He received the prestigious Cullum Medal of the American Geographical Society and the Outstanding Achievement Award from the Association of American Geographers. In The Task Ahead, published in 1961, Thornthwaite provided young scholars with a vision of the task ahead in climatology—a vision valid to this day and one that included scientific grounding in energy and water budget theory and analyses. Last was his contribution to urban geography through his dissertation under Carl Sauer. Thornthwaite's approach was a classic one in what was later to become a strong spatial tradition in the discipline.