Previously Reported Evaporation Rates

The reported average annual evaporation of 6.4 ft from 1953 through 1994 (fig. 11, table 8) is 15 percent less than the estimated average annual evaporation of 7.5 ft from 1997 to 1999. The USGS reported monthly evaporation rates for Lake Mead from October 1953–September 1995 (U.S. Geological Survey, 1961–64, 1965–75, 1976–82; Hendricks, 1964; Frisbie and others, 1983–85; Pupacko and others, 1988, 1989a, 1989b, 1990; Bostic and others, 1991; Garcia and others, 1992; Hess and others, 1993; Emett and others, 1994; Clary and others, 1995; Bauer and others, 1996). Harbeck (1958b, table 13, p. 37) reported monthly evaporation rates for March 1952 to September 1953. G.E. Koberg (U.S. Geological Survey, written commun., 1964) revised the reported monthly evaporation rates for October 1952 to September 1962; however, those revised rates were never published. Koberg did not revise the reported monthly rates for March 1952 to September 1952. Previously reported evaporation rates were not entered in a database or summarized in any single publication; these rates were available only from the various publications and written communications.

The average annual evaporation, average monthly evaporation, and standard deviation of monthly rates were compared for two periods of previously estimated Lake Mead evaporation, 1953–73 and 1974–94. Evaporation rates were available for 12 months of each year during those periods and each period consists of 21 years (table 8). The average annual evaporation for 1953–73 is 6.7 ft; whereas, the average annual evaporation for 1974–94 is 6.0 ft. Compared to 1974–94, the mean monthly evaporation during 1953–73 was greater for every month except November.

The standard deviation (variability) of monthly evaporation rates for 1953–73 was less than for 1974–94 for every month except May. Only the annual rates of 5.9 ft in 1965 and 7.4 ft in 1956 differed from the average annual rate of 6.7 ft for 1953–73 by greater than 10 percent. In contrast, annual evaporation was more variable for 1974–94 with rates for 9 years that differed by more than 10 percent from the average annual rate of 6.0 ft. The greater variability probably was related to estimated monthly wind speed due to mechanical problems with the anemometer at Lake Mead.

Back to Table of Contents

Accessibility FOIA Privacy Policies and Notices

U.S. Department of the Interior | U.S. Geological Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065252
Page Contact Information: Publications Team
Page Last Modified: Thursday, 01-Dec-2016 19:29:18 EST