Computing composite indices (wsim_composite
)ΒΆ
The wsim_composite
utility computes Composite Indices from multiple surplus and deficit input variables.
The composite indices are output to a netCDF file with the following variables:
surplus
the worst (most positive) return period of all input surplus variables
surplus_cause
a coded variable indicating which of the surplus variables was responsible for the composite surplus indicator value
deficit
the worst (most negative) return period of all input deficit variables
deficit_cause
a coded variable indicating which of the deficit variables was responsible for the composite deficit indicator value
both
the greater magnitude of
surplus
anddeficit
, whenever both of these indices have a magnitude higher than a specified threshold
Usage is as follows:
Usage: wsim_composite \
(--surplus=<file>)... \
(--deficit=<file>)... \
--both_threshold=<value> \
[--mask=<file>] \
--output=<file>
The --surplus
and --deficit
arguments are used to specify variables that should be considered in computing the composite surplus and deficit indices.
each argument may refer to more than one variable, and each argument may be provided multiple times. The WSIM variable definition notation is fully supported.
The --both_threshold
argument specifies the minimum magnitude of the composite surplus and deficit indices for a pixel to be considered to simultaneously experience surplus and deficit.
The --mask
allows an optional mask to be defined, so that all composite indices have the same maximum extent even if the input datasets do not.
As a more complete example, the following command was is used to produce the WSIM composite indices for January 2017 from multiple raster inputs:
./wsim_composite.R \
--deficit "~/freq/PETmE_freq_trgt201701.img::1@fill0@negate->Neg_PETmE" \
--deficit "~/freq/Ws_freq_trgt201701.img::1->Ws" \
--deficit "~/freq/Bt_RO_freq_trgt201701.img::1->Bt_RO" \
--surplus "~/freq/Bt_RO_freq_trgt201701.img::1->Bt_RO" \
--surplus "~/freq/RO_mm_freq_trgt201701.img::1->RO_mm" \
--mask "~/freq/Ws_freq_trgt201701.img" \
--both_threshold 3 \
--output "/tmp/composite_201701.nc"
A few points are worth noting in this example:
The
Bt_RO
variable is considered in computation of both the surplus and deficit indices.The
PETmE
variable is transformed by filling NODATA values with zero, and then negating all values.The
Ws
variable was used as a mask for the composite indices. If this were not done, the composite deficit would be populated in all pixels, because of the transformation done toPETmE
.