Calculate a timeseries of ETo across a set of input rasters.

Assumes that all inputs share the same resolution, extent, projection. Also assumes that rasters have the number of layers with each layer corresponding to a day. For hargreaves, only t_mean, t_min and t_max are required arguments. For PM, t_mean, srad, rh, and ws must all be supplied.

Usage

calc_etr_spatial(
  t_mean = NULL,
  t_min = NULL,
  t_max = NULL,
  srad = NULL,
  rh = NULL,
  rh_min = NULL,
  rh_max = NULL,
  ws = NULL,
  elev = NULL,
  days = NULL,
  reference = 0.23,
  z = 9,
  wind_height = 2,
  method = "penman"
)

Arguments

t_mean: A multilayer timeseries terra::rast of mean daily temperature in degrees C.
t_min: A multilayer timeseries terra::rast of max daily temperature in degrees C.
t_max: A multilayer timeseries terra::rast of min daily temperature in degrees C.
srad: A multilayer timeseries terra::rast of daily solar radiation in W m^-2.
rh: A multilayer timeseries terra::rast of mean daily relative humidity (%).
rh_min: A multilayer timeseries terra::rast of minimum daily relative humidity (%; defaults to NULL).
rh_max: A multilayer timeseries terra::rast of maximum daily relative humidity (%).
ws: A multilayer timeseries terra::rast of mean daily wind speed at 2m height in m s^-1.
elev: A terra::rast of elevation in meters. If left blank, elevation will be derived using the elevatr package.
days: A multilayer timeseries terra::rast where each day is a constant value of the Julian day. If left blank, it is assumed the t_mean input has a time attribute and the raster will be derived using terra::time.
reference: The albedo of the reference surface ranging from 0 - 1. Defaults to 0.23 for grass.
z: The zoom level download elevation data at ranging from 1 - 14. One if coarser resolution, 14 is finer resolution. For more information, look at ?elevatr::get_elev_raster
wind_height: The height of the wind observation in meters. (defaults to 2). If it is not 2 meters, the wind speed will be corrected to a 2 meter observation.
method: The method to calculate ETo. Can either be "penman" or "hargreaves".

Value

A terra::rast timeseries of ETo for the input domain.

Examples

if (FALSE) {
# Load data. Need to read with terra::rast to unpack to a raster.
srad <- terra::rast(srad) |> terra::subset(1:10)
t_mean <- terra::rast(t_mean) |> terra::subset(1:10)
# Convert from K to C
t_mean <- t_mean - 273.15
t_max <- terra::rast(t_max) |> terra::subset(1:10)
# Convert from K to C
t_max <- t_max - 273.15
t_min <- terra::rast(t_min) |> terra::subset(1:10)
# Convert from K to C
t_min <- t_min - 273.15
rh <- terra::rast(rh) |> terra::subset(1:10)
ws <- terra::rast(ws) |> terra::subset(1:10)

penman <- calc_etr_spatial(
  t_mean = t_mean, srad = srad, rh = rh, ws = ws,
  method = "penman", reference = 0.23, z = 3
)
hargreaves <- calc_etr_spatial(
  t_mean = t_mean, t_max = t_max, t_min = t_min, method = "hargreaves", z = 3
)
}