How to Convert xarray Units from Celsius to Kelvin

This how-to shows how to convert the values of an xarray.DataArray (or xarray.Dataset) from degrees Celsius to Kelvin using earthkit.utils.units.convert_units.

import xarray as xr

from earthkit.utils.units import convert_units

Convert a DataArray

Create a DataArray with a units attribute set to "degC". The converter reads source units from the attribute automatically, so only target_units needs to be specified.

temperature = xr.DataArray(
    [0.0, 20.0, 100.0],
    dims="x",
    name="temperature",
    attrs={"units": "degC"},
)

temperature_K = convert_units(temperature, target_units="K")
print(temperature_K.values)  # [273.15 293.15 373.15]
print(temperature_K.attrs["units"])  # K

[273.15 293.15 373.15]
K

Override Source Units Explicitly

If the units attribute is absent or incorrect, pass source_units to override it:

# DataArray without a units attribute
temperature_no_attr = xr.DataArray([0.0, 20.0, 100.0], dims="x")

temperature_K = convert_units(
    temperature_no_attr,
    target_units="K",
    source_units="degC",
)
print(temperature_K.values)  # [273.15 293.15 373.15]

[273.15 293.15 373.15]

Convert a Dataset

Use a target_units dict to specify the target unit per variable. Only the named variable is converted; others are left unchanged.

ds = xr.Dataset({
    "temperature": xr.DataArray([0.0, 20.0], dims="x", attrs={"units": "degC"}),
    "pressure": xr.DataArray([1013.25, 1000.0], dims="x", attrs={"units": "hPa"}),
})

result = convert_units(ds, target_units={"temperature": "K"})
print(result["temperature"].values)  # [273.15 293.15]
print(result["temperature"].attrs["units"])  # K
print(result["pressure"].values)  # [1013.25 1000.  ] — unchanged

[273.15 293.15]
K
[1013.25 1000.  ]