BUG: time coordinate not properly set to the middle of the sampling period
Closed this issue · 3 comments
bzah commented
- icclim version: ?
- Python version: ?
Description
Initially reported by email.
I am using your library to calculate the SPI6 climate index but I don't understand the results it gives me, I don't know if there is a bug. I send the netcdf that I'm using and this is the code that I'm using from you:
import icclim
dataset = icclim.index(
index_name="spi6",
in_files=dataset,
var_name="pr",
base_period_time_range=baseline_period_time_range,
).load()and the result looks like this:
<xarray.Dataset>
Dimensions: (lat: 192, lon: 288, time: 12, bounds: 2)
Coordinates:
* lat (lat) float64 -90.0 -89.06 -88.12 -87.17 ... 88.12 89.06 90.0
* lon (lon) float64 -178.8 -177.5 -176.2 -175.0 ... 177.5 178.8 180.0
height float64 2.0
* time (time) datetime64[ns] 2015-07-02 ... 2015-12-16
* bounds (bounds) int64 0 1
Data variables:
SPI6 (time, lat, lon) float64 nan nan nan nan ... nan nan nan nan
time_bounds (time, bounds) datetime64[ns] 2015-01-01 ... 2015-12-31
Attributes:
title: spi
references: ATBD of the ECA&D indices calculation (https://knmi-ecad-as./..
institution: Climate impact portal (https://climate4impact.eu/)
history: [2023-05-25 14:06:10] spi: SPI(pr=pr, pr_cal=pr, freq='MS',...
source:
Conventions: CF-1.6 The time dimension is supposed to start in january.
The bug is due to the post_processing step that is meant to add time_bounds but also resample the result if necessary.
This step should probably be avoided when computing SPI6 or SPI3.
Investigation needed to see if other indices are impacted.
bzah commented
Workaround until the issue is fixed, using xclim:
import xclim
import xarray as xr
ds = xr.open_dataset("pr.nc")
base_pr = ds.pr.sel(time=slice("2015-01-01","2015-06-31"))
xclim.atmos.standardized_precipitation_index(
pr=ds.pr,
pr_cal=base_pr,
freq="MS",
window=6,
dist="gamma",
method="APP"
)