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Effect of using averaged data on the computed evaporation
Author(s) -
Jobson Harvey E.
Publication year - 1972
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr008i002p00513
Subject(s) - evaporation , interval (graph theory) , mathematics , statistics , wind speed , pan evaporation , meteorology , environmental science , atmospheric sciences , geology , physics , combinatorics
Because it is seldom necessary to determine the total evaporation from a body of water for short periods of time, it is tempting to use meteorologic parameters that have been averaged over long intervals of time and the semiempirical mass transfer equation to determine the total evaporation. This paper illustrates the effect of time in averaging wind speeds and temperatures on the computed evaporation. Data collected during a 15‐month interval at Lake Hefner near Oklahoma City, Oklahoma, were analyzed. Each set of data represents the average meteorologic conditions during a 30‐minute time interval. From these data the effect of averaging for periods of 3 hours, 1 day, and 1 month was determined. The value of the coefficient in the semiempirical mass transfer formula is shown to be independent of the averaging time when this time is less than 1 day in length. The frequency distribution of the averaging error was determined for each averaging period. An averaging error larger than ±5% occurred about 3% of the time for 3‐hour averages and about 20% of the time for daily averages. It is concluded that averaging periods of 1 month should be avoided in situations similar to those at Lake Hefner.