In NCAR/rwrfhydro: R tools for the WRF Hydro Model

Background

Pull SNODAS data and collect into a "database" of local netcdf files.

Setup

Load the rwrfhydro package.

library("rwrfhydro")

options(width = 120, warn=1)

This is the path to the directory where you want your database to be built (it should exist and be empty for the purposes of this example):

snodasPath <- '~/wrfHydroTestCases/snodas/' 
if(dir.exists(snodasPath)) file.remove(list.files(snodasPath,'.', full.names=TRUE))
dir.create(snodasPath)

Get some data

Grab a single date (both depth and SWE) and transform to netcdf. For the sake of illustration, grab three days ago.

threeDaysBack <- Sys.Date() + lubridate::period(-3,'day')
snodasGot <- GetSnodasDepthSweDate(threeDaysBack, outputDir=snodasPath, overwrite=TRUE)
if(snodasGot) {
  snodasList <- ReadSnodasDepthSweDate(threeDaysBack, outputDir=snodasPath)
  snodasNcFile <- PutSnodasNcdf(snodasList, outputDir=snodasPath)
  snodasNcFile
}

Read ncdf and visualize

swe <- ncdump(snodasNcFile, variable = 'SWE')
## Filter outliers.
swe[swe>quantile(as.vector(swe), .999, na.rm=TRUE)] <- NA
image(swe)

Update

The above can be repeated over multiple dates one might want to get, for example from three days ago until now

datesWanted <- seq(threeDaysBack, Sys.Date(), by = 'days')
datesWanted

Encapsulate the above in a function with some file existance checking and return summary.

UpdateSnodas <- function(POSIXct, outPath='.') {
  ## check if we already processed this date/POSIXct, if we didnt process, we'll
  ## download again and process it. (note we could have downloaded but not processed 
  ## so it might not be efficient). 
  file <- paste0(outPath, 'SNODAS_',format(POSIXct,'%Y%m%d'),'.nc')
  processed <- file.exists(file)
  if(processed) 
    return(data.frame(date=POSIXct, snodasGot=FALSE, ncdfFile=file))

  snodasGot <- GetSnodasDepthSweDate(POSIXct, outputDir=outPath)
  if(snodasGot) {
    snodasList <- ReadSnodasDepthSweDate(POSIXct, outputDir=outPath)
    ncdfFile <- PutSnodasNcdf(snodasList, outputDir=outPath)
  } else ncdfFile <- ''
  data.frame(date=POSIXct, snodasGot=snodasGot, ncdfFile=ncdfFile)
}

update <- plyr::ldply(NamedList(datesWanted), UpdateSnodas, outPath=snodasPath)
update