fruclimadapt (version 0.4.5)

ET_penman_monteith: Calculation of daily reference evapotranspiration by Penman-Monteith method

Description

This function calculates the reference evapotranspiration (ETref) for short (ETos) and tall (ETrs) canopies using daily weather data. The method is based on the FAO56 guidelines (Allen et al, 1998) and on the standardized Penman Monteith equation from the Environmental Water Resources Institute of the American Society of Civil Engineers (Allen et al, 2005).

Usage

ET_penman_monteith(climdata, lat, elev)

Value

dataframe with Year, Month, Day, DOY, ETos and ETrs values.

Arguments

climdata

a dataframe with daily weather data. Required columns are Year, Month, Day, Tmax and Tmin. Optional columns are RHmax, RHmin, Rad and u2med.

lat

the latitude of the site, in decimal degrees.

elev

the elevation of the site, in meters above sea level.

Author

Carlos Miranda,

Details

Minimum data requirements to calculate ET are daily temperatures (maximum and minimum temperatures, Tmax and Tmin), whereas relative humidity (RHmax and RHmin), solar radiation (Rad, MJ m-2 day-1) and mean wind speed at 2m height (u2med,m s-1) are optional. If missing, the function integrates FAO56 estimations for solar radiation and vapor pressure (air humidity) from daily temperatures. If there is no information available on wind speed, the function assumes a constant value of 2 m s-1.

References

Allen RG, Pereira LS, Raes D, Smith M. 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrigation and drainage paper 56. Food and Agriculture Organization of the United Nations

Allen RG, Walter IA, Elliott RL, Howell TA, Itenfisu D, Jensen ME, Snyder RL 2005. The ASCE standardized reference evapotranspiration equation. Reston, VA:American Society of Civil Engineers. 59 p.

Examples

# Calculate ET by Penman-Monteith method in the Tudela_DW example dataset
library(magrittr)
library(dplyr)
elevation <- 314
latitude <- 42.13132
ET_PM <- ET_penman_monteith(Tudela_DW, latitude, elevation)