Degday: A Program for Calculating Degree-days, and Assumptions Behind the Degree-day Approach

Abstract

A BASIC computer program (DEGDAY) for calculating degree-days on microcomputers is presented. The program calculates heating degree-days with the rectangle, triangle, and sine wave methods and calculates cooling degree days with the sine wave method. Assumptions and approximations associated with degree-day calculations are noted. In particular, eight factors affecting degree-days are discussed: 1) substrate availability, 2) enzyme availability, 3) approximations in laboratory estimates of development, 4) approximations in calculating the developmental minimum, 5) approximations in calculating a developmental maximum, 6) approximations in using single values for thresholds, 7) thermoregulation, and 8) limitations of temperature data. The various errors arising from these factors are discussed in relationship to error attributable to differences between actual and estimated degree-days.