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Gettings started with AWAPer

Source: vignettes/AWAPer.Rmd
AWAPer.Rmd

Introduction

To get started, the key steps are:

  1. Build the required netCDF grids of weather data.
  2. Extract the required weather data at user defined locations, duration and time-step.
  3. Update the data grids as new data becomes available.

Each of the steps is outlined below.

Build netCDF data

The netCDF data grids are created using the function makeNetCDF_file. This requires user input of the following:

  1. ncdfFilename to define where the netCDF file should be created. Note, using the default compression settings, each meteorological variable requires ~5GB of hard-drive storage for the full record (1900 to now). Additionally, the netCDF files should be stored locally, and not over a network, to minimise the time for data extraction.
  2. updateFrom : start date for the data. Users often set this to the default date as.Date('1900-01-01') to extract all available data.
  3. updateTo : end date for the data. Users often set this to the default date of two days ago to extract all available data.
  4. urlPrecip etc to define which meteorological variables are to be input to the netCDF data grids. Setting any of them to NA causes that variable to not be included in the netCDF data grids.

See here for an example of how to build your first netCDF data file.

Extract weather data

Once the netCDF data grids are created, extract data using the extractCatchmentData function. The essential user inputs are:

  1. ncdfFilename file name pointing to the netCDF file.
  2. locations defining the locations at which the data is to be xtracted. it can be a full file name to an ESRI shape file of points or polygons or a shape file already imported using readShapeSpatial(). Either way the shape file must be in long/lat (i.e. not projected), use the ellipsoid GRS 80, and the first column must be a unique ID.

Many other user controls are available that control the duration, time-step, the spatial and temporal aggregation (e.g. mean, sum, min or max), the meteorological variables required and the measure of evapotranspiration. For examples of time-series extractions see here and here. For examples of spatial data extractions see here).

Update netCDF data

Over time, the existing netCDF data can be updated using the function makeNetCDF_file. Specifically, when an existing netCDF file is input, then the function updates the data between updateFrom and updateTo. These dates are automatically adjusted to ensure there are not date gaps in the data grids. Also, any data outside this periuod is not modified. See here for an exanmple.