Evaluation of several degree-day estimation methods in California climates |
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Authors: | William J Roltsch Frank G Zalom Ann J Strawn Joyce F Strand Michael J Pitcairn |
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Institution: | (1) Statewide IPM Project, University of California, Davis, California, CA 95616-8621, USA, US;(2) California Deptartment of Food and Agriculture, Biological Control Program, 3288 Meadowview Road, Sacramento, CA 95832, USA, US |
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Abstract: | Procedures for estimating degree-day accumulations are frequently employed instead of the more accurate method of calculating
degree-days from hourly temperature data because on-site temperature data are commonly restricted to daily minimum and maximum
temperature records. Data from seven methods of estimating degree-days at each of nine locations during 2 years in California
were compared by month to degree-day values calculated by hourly summation. Methods included three sine-wave approaches, three
triangulation approaches and the averaging (i.e., rectangle) method. Results of the double-sine and corrected-sine (i.e.,
corrected for day length) methods were nearly identical to those of the single-sine method. The double triangulation and corrected
triangulation methods produced very similar results to the single triangulation method. The averaging method and sine-wave
methods deviated to a greater extent from degree-day accumulations calculated from hourly temperatures from November through
February than did the triangulation methods. Degree-day estimations from the late spring and summer months were more similar
to one another for all estimation methods than during the cooler months of the year. Since no advantages were noted in the
more complicated double and corrected methods, the single triangulation method or the sine-wave method is preferred as they
are less complicated procedures. Of the various temperature threshold cut-off methods evaluated, error levels were unaffected
when estimating degree-days using the sine-wave method. The employment of a horizontal cut-off with the triangulation method
did not significantly increase the amount of error in the estimation of degree-days. However, an increase in error was observed
when employing the intermediate cut-off and vertical threshold cut-off techniques with the triangulation method for computing
degree-days.
Received: 26 May 1998 / Accepted: 28 October 1998 |
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Keywords: | Degree-days Temperature effects Phenology models Developmental threshold Thermal unit |
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