chillR (version 0.75)

GDD: Calculation of cumulative heat according to the Growing Degree Day Model

Description

This function calculates heat for temperate trees according to the Growing Degree Day Model. Note that the calculuation differs slightly from the original, in which it is based on daily temperature extremes only. This equation here works with hourly temperatures. The normal GDD equation is GDD=(Tmax-Tmin)/2-Tbase, with Tmax=30 for Tmax>30, and Tmin=10 for Tmin<10. Tbase is a species-specific base temperature. The first part of the equation is the arithmetic mean of daily temperature extremes. In the present equation, this is replaced by Thourly/24 for each hourly temperature value. If chillR was using a triangular daily temperature curve, the result would be the same for both equations. Since chillR uses a sine function for daytime warming and a logarithmic decay function for nighttime cooling, however, there will be a slight deviation. This could be handled by defining a function the runs with daily weather data. chillR doesn't currently have this capability, since its primary focus is on metrics that require hourly data.

Usage

GDD(HourTemp, summ = TRUE, Tbase = 5)

Value

Vector of length length(HourTemp) containing the cumulative Growing Degree Days over the entire duration of HourTemp.

Arguments

HourTemp

Vector of hourly temperatures.

summ

Boolean parameter indicating whether calculated metrics should be provided as cumulative values over the entire record (TRUE) or as the actual accumulation for each hour (FALSE).

Tbase

Base temperature, above which Growing Degrees accrue.

Author

Eike Luedeling

Details

Growing Degree Hours are calculated as suggested by Anderson et al. (1986).

References

Growing Degree Days reference:

http://agron-www.agron.iastate.edu/Courses/agron212/Calculations/GDD.htm

Examples

weather<-fix_weather(KA_weather[which(KA_weather$Year>2006),])

hourtemps<-stack_hourly_temps(weather,latitude=50.4)

GDD(hourtemps$hourtemps$Temp)