ClimDown (version 1.0.8)

rerank.netcdf.wrapper: High-level NetCDF wrapper for Quantile Reranking

Description

Quantile Reranking is the final, critical step in the BCCAQ pipeline. Its purpose is this: since Climate Analogues (CA) gets its high resolution information by using a linear combination of historical daily time series for the domain as a whole, it ends up reintroducing some bias. This is because the quantile mapping bias correction step was performed only at course resolution (of the GCM). Quantile Reranking fixes this by re-applying a simple quantile mapping bias correction at each grid box. The advantage of doing this as a final step is that the downscaling method retains the primary advantage of BCCA: high spatial consistency (e.g. when a storm or a heat wave hits a specific area, it probably also hits neighboring areas, etc.).

Usage

rerank.netcdf.wrapper(
  qdm.file,
  obs.file,
  analogues,
  out.file,
  varname = "tasmax"
)

Arguments

qdm.file

The output file from the QDM script

obs.file

Filename of high-res gridded historical observations

analogues

Temporal analogues. This is a list of two arrays: the index values and the fractional weights. Each array is the length of the number of timesteps by k (typically 30).

out.file

The file to create (or overwrite) with the final NetCDF output

varname

Name of the NetCDF variable to downscale (e.g. 'tasmax')

Details

All input files (save for the analogues_file) should have the same spatial domain.

References

Schefzik, R., Thorarinsdottir, T. L., & Gneiting, T. (2013). Uncertainty quantification in complex simulation models using ensemble copula coupling. Statistical Science, 28(4), 616-640.

Wilks, D. S. (2015). Multivariate ensemble Model Output Statistics using empirical copulas. Quarterly Journal of the Royal Meteorological Society, 141(688), 945-952.

Examples

# NOT RUN {
options(
    calibration.end=as.POSIXct('1972-12-31', tz='GMT')
)
ci.file <- tempfile(fileext='.nc')
ClimDown::ci.netcdf.wrapper('./tiny_gcm.nc', './tiny_obs.nc', ci.file, 'tasmax')
qdm.file <<- tempfile(fileext='.nc')
ClimDown::qdm.netcdf.wrapper('./tiny_obs.nc', ci.file, qdm.file, 'tasmax')
unlink(ci.file)
analogues <<- ClimDown::ca.netcdf.wrapper('./tiny_gcm.nc', './tiny_obs.nc')
out.file <- tempfile(fileext='.nc')
ClimDown::rerank.netcdf.wrapper(qdm.file, './tiny_obs.nc', analogues, out.file, varname='tasmax')
unlink(qdm.file)
unlink(out.file)
# }
# NOT RUN {
# }