In ldemaz/rcropmod: Crop model simulations in R

knitr::opts_chunk$set(echo = TRUE, message = FALSE, collapse = T, 
                      comment = "#>")

We will use the weathdat dataset, which comes with the rcropmod, to provide an example of how to make a DSSAT WTH file. For this we use the rcropmod function weather.

Create weather file

DSSAT weather files can contain a number of different variables, but at a minimum need daily TMin, TMax, rainfall, and average shortwave radiation. This will allow DSSAT to calculate evapotranspiration using the Priestly-Taylor equation. It can use the more physically realistic FAO56 routine if you can also provide dew point temperature and windspeed. We don't usually have dew point, but the weather function draws on dew_point to calculate this variable from either relative humidity and temperature or specific humidity and pressure. Here we will use the latter two variables.

library(rcropmod)
name <- "TEST"
outdir <- "~/DSSAT45/Weather/"
wdat <- weathdat$dat
weathdat$dat[, weather(xy = weathdat$xyz[c("lat", "lon")], 
                       elev = weathdat$xyz["elev"], srad = sw, tmax = tmax,
                       tmin = tmin, prec = prec, wind = wind, sh = sh, 
                       pres = pres, sdate = weathdat$dates["start"], 
                       edate = weathdat$dates["end"], name = name, 
                       outdir = outdir)]

Quality check the WTH file

It's not a bad idea to look at the resulting file to make sure the values make sense, there are missing dates, etc. Here are a few examples of checks with R.

wth <- read.table(file = paste0(outdir, "/TEST7932.WTH"), skip = 4, 
                     sep = "", header = TRUE, stringsAsFactors = FALSE)

ymd <- seq(as.Date(weathdat$dates["start"],"%Y%m%d"), 
           as.Date(weathdat$dates["end"],"%Y%m%d"), by = 1)
length(ymd) == length(weathdat$dat[, wind])  # true
nrow(wth) == length(ymd)

# Make sure there are no missing dates - this causes failures
max(sapply(2:length(wth$X.DATE), function(i) {
   as.Date(sprintf("%05s", wth$X.DATE[i]), "%y%j") - 
      as.Date(sprintf("%05s", wth$X.DATE[i - 1]), "%y%j") 
}))