An improved model for determining degree-day values from daily temperature data |
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Authors: | C Cesaraccio D Spano P Duce R L Snyder |
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Institution: | (1) Istituto per il Monitoraggio degli Agroecosistemi, CNR, Via Funtana di Lu Colbu, 4A, 07100 Sassari, Italy e-mail: cesaraccio@imaes.ss.cnr.it Tel.: +39-079-268246, Fax: +39-079-268248, IT;(2) Dipartimento di Produzione Vegetale, Università della Basilicata, Potenza, Italy, IT;(3) Department of Land, Air and Water Resources, University of California, Davis, Calif., USA, US |
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Abstract: | Although using hourly weather data offers the greatest accuracy for estimating growing degree-day values, daily maximum and
minimum temperature data are often used to estimate these values by approximating the diurnal temperature trends. This paper
presents a new empirical model for estimating the hourly mean temperature. The model describes the diurnal variation using
a sine function from the minimum temperature at sunrise until the maximum temperature is reached, another sine function from
the maximum temperature until sunset, and a square-root function from then until sunrise the next morning. The model was developed
and calibrated using several years of hourly data obtained from five automated weather stations located in California and
representing a wide range of climate conditions. The model was tested against an additional data-set at each location. The
temperature model gave good results, the root-mean-square error being less than 2.0 °C for most years and locations. The comparison
with published models from the literature showed that the model was superior to the other methods. Hourly temperatures from
the model were used to calculate degree-day values. A comparison between degree-day estimates determined from the model and
those obtained other selected methods is presented. The results showed that the model had the best accuracy in general regardless
of the season.
Received: 25 October 2000 / Revised: 2 July 2001 / Accepted: 2 July 2001 |
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Keywords: | Maximum temperature Minimum temperature Daily temperature trend Degree-days Phenology |
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