precipitation-efficiency index Devised in 1931 by C. W. Thornthwaite, an index based on the ratio of mean monthly rainfall and temperature values to evaporation rates. Summation of monthly values gives an annual precipitation-efficiency index (P-E), which is used to define major climatic regions. See also THORNTHWAITE CLIMATE CLASSIFICATION.

precipitation-efficiency index Devised in 1931 by C. W. Thornthwaite, an index based on the ratio of mean monthly rainfall and temperature values in relation to evaporation rates. Summation of monthly values gives an annual precipitation-efficiency index (P–E), which is used to define major climatic regions. See also Thornthwaite climate classification.

precipitation-efficiency index Devised in 1931 by C. W. Thornthwaite, an index based on the ratio of mean monthly rainfall and temperature values to evaporation rates. Summation of monthly values gives an annual precipitation-efficiency index (P–E), which is used to define major climatic regions.