Source code for icclim.main

# -*- Coding: latin-1 -*-
#  Copyright CERFACS (
#  Apache License, Version 2.0 (
Main entry point of icclim.

This module expose icclim principal function, notably `index` which is use by the
generated API.
A convenience function `indices` is also exposed to compute multiple indices at once.
from __future__ import annotations

import datetime as dt
import time
from import Sequence
from functools import partial, reduce
from typing import TYPE_CHECKING, Callable, Literal
from warnings import warn

import xarray as xr
import xclim

from icclim.ecad.ecad_indices import EcadIndexRegistry
from icclim.ecad.xclim_binding import XclimBinding
from icclim.generic_indices.generic_indicators import (
from icclim.generic_indices.threshold import Threshold, build_threshold
from icclim.icclim_exceptions import InvalidIcclimArgumentError
from icclim.icclim_logger import IcclimLogger, Verbosity, VerbosityRegistry
from icclim.models.climate_variable import (
from icclim.models.constants import (
from icclim.models.frequency import Frequency, FrequencyRegistry
from icclim.models.index_config import IndexConfig
from icclim.models.index_group import IndexGroup, IndexGroupRegistry
from icclim.models.logical_link import LogicalLink, LogicalLinkRegistry
from icclim.models.netcdf_version import NetcdfVersion, NetcdfVersionRegistry
from icclim.models.operator import Operator, OperatorRegistry
from icclim.models.quantile_interpolation import (
from icclim.user_indices.calc_operation import CalcOperationRegistry
from icclim.utils import read_date

    from xarray.core.dataarray import DataArray
    from xarray.core.dataset import Dataset

    from icclim.icclim_types import FrequencyLike, InFileLike, SamplingMethodLike
    from icclim.models.standard_index import StandardIndex
    from icclim.models.user_index_dict import UserIndexDict
    from icclim.pre_processing.in_file_dictionary import InFileDictionary

log: IcclimLogger = IcclimLogger.get_instance(VerbosityRegistry.LOW)

HISTORY_CF_KEY = "history"
SOURCE_CF_KEY = "source"

def indices(
    index_group: str | IndexGroup | Sequence[str],
    ignore_error: bool = False,
) -> Dataset:
    Compute multiple indices at the same time.
    The input dataset(s) must include all the necessary variables.
    It can only be used with keyword arguments (kwargs).

    .. notes
        If ``output_file`` is part of kwargs, the result is written in a single netCDF
        file, which will contain all the index results of this group.

    index_group : "all" | str | IndexGroup | list[str]
        Either the name of an IndexGroup or an instance of IndexGroup or a list
        of index short names or the name(s) of standard variable(s) (such as 'tasmax').
        The value "all" can also be used to compute every indices.
        Note that the input given by ``in_files`` must include all the necessary
        variables to compute the indices of this group.
    ignore_error: bool
        When True, ignore indices that fails to compute. This is option is particularly
        useful when used with `index_group='all'` to compute everything that can be
        computed given the input.
    kwargs : Dict
        ``icclim.index`` keyword arguments.

        A Dataset with one data variable per index.

    indices = _get_indices_of_group(index_group)
    out = None
    if "out_file" in kwargs:
        out = kwargs["out_file"]
        del kwargs["out_file"]
    acc = []
    for i in indices:"Computing index %s", i.short_name)
        kwargs["index_name"] = i.short_name
        if ignore_error:
                res = index(**kwargs)
                if "percentiles" in res.coords:
                    res = res.rename({"percentiles": i.short_name + "_percentiles"})
                if "thresholds" in res.coords:
                    res = res.rename({"thresholds": i.short_name + "_thresholds"})
            except Exception:  # noqa: BLE001 (catch everything)
                warn(f"Could not compute {i.short_name}.", stacklevel=2)
            res = index(**kwargs)
            if "percentiles" in res.coords:
                res = res.rename({"percentiles": i.short_name + "_percentiles"})
            if "thresholds" in res.coords:
                res = res.rename({"thresholds": i.short_name + "_thresholds"})
    ds: Dataset = xr.merge(acc)
    if out is not None:
            netcdf_version=kwargs.get("netcdf_version", NetcdfVersionRegistry.NETCDF4),
    return ds

def _get_indices_of_group(
    query: list | tuple | str | IndexGroup | StandardIndex,
) -> list[StandardIndex]:
    if query == IndexGroupRegistry.WILD_CARD_GROUP or (
        isinstance(query, str)
        and query.lower() ==
        # case of group="all"
        return EcadIndexRegistry.values()
    if not isinstance(query, (list, tuple)):
        query = [query]
    # -- Look for standard indices (e.g. index_group='tx90p')
    indices = [EcadIndexRegistry.lookup(i, no_error=True) for i in query]
    indices = list(filter(lambda x: x is not None, indices))
    if len(indices) == len(query):
        return indices
    # -- Look for variables in standard indices (e.g. index_group='tasmax')
    indices = []
    for ecad_index in EcadIndexRegistry.values():
        has_var = True
        for var in ecad_index.input_variables:
            is_query_in_aliases = (
                standard_var in var.aliases for standard_var in query
            has_var &= any(is_query_in_aliases)
        if has_var:
    if len(indices) >= len(query):
        return indices
    # -- Look for index group (e.g. index_group='HEAT')
    groups = [IndexGroupRegistry.lookup(i, no_error=True) for i in query]
    groups = list(filter(lambda x: x is not None, groups))
    indices = (x.get_indices() for x in groups)
    indices = reduce(lambda x, y: x + y, indices, [])  # flatten list[list]
    if len(indices) >= len(query):
        return indices
    msg = f"The index group {query} was not recognized."
    raise InvalidIcclimArgumentError(msg)

def indice(*args, **kwargs) -> Dataset:
    Deprecated proxy for `icclim.index` function.
    To be deleted in a futur version.
    log.deprecation_warning(old="icclim.indice", new="icclim.index")
    return index(*args, **kwargs)

[docs] def index( in_files: InFileLike, index_name: str | None = None, # optional when computing user_indices var_name: str | Sequence[str] | None = None, slice_mode: FrequencyLike | Frequency = "year", time_range: Sequence[dt.datetime | str] | None = None, out_file: str | None = None, threshold: str | Threshold | Sequence[str | Threshold] = None, callback: Callable[[int], None] = log.callback, callback_percentage_start_value: int = 0, callback_percentage_total: int = 100, base_period_time_range: Sequence[dt.datetime] | Sequence[str] | None = None, doy_window_width: int = 5, only_leap_years: bool = False, ignore_Feb29th: bool = False, # noqa: N803 interpolation: str | QuantileInterpolation = "median_unbiased", out_unit: str | None = None, netcdf_version: str | NetcdfVersion = "NETCDF4", user_index: UserIndexDict | None = None, save_thresholds: bool = False, logs_verbosity: Verbosity | str = "LOW", date_event: bool = False, min_spell_length: int | None = 6, rolling_window_width: int | None = 5, sampling_method: SamplingMethodLike = RESAMPLE_METHOD, *, # deprecated params are kwargs only window_width: int | None = None, save_percentile: bool | None = None, indice_name: str | None = None, user_indice: UserIndexDict = None, transfer_limit_Mbytes: float | None = None, # noqa: N803 ) -> Dataset: """ Main entry point for icclim to compute climate indices. Parameters ---------- in_files: str | list[str] | Dataset | DataArray | InputDictionary Absolute path(s) to NetCDF dataset(s), including OPeNDAP URLs, or path to zarr store, or xarray.Dataset or xarray.DataArray. index_name: str Climate index name. For ECA&D index, case insensitive name used to lookup the index. For user index, it's the name of the output variable. var_name: str | list[str] | None ``optional`` Target variable name to process corresponding to ``in_files``. If None (default) on ECA&D index, the variable is guessed based on the climate index wanted. Mandatory for a user index. slice_mode: SliceMode Type of temporal aggregation: The possibles values are ``{"year", "month", "DJF", "MAM", "JJA", "SON", "ONDJFM" or "AMJJAS", ("season", [1,2,3]), ("month", [1,2,3,])}`` (where season and month lists can be customized) or any valid pandas frequency. A season can also be defined between two exact dates: ``("season", ("19 july", "14 august"))``. Default is "year". See :ref:`slice_mode` for details. time_range: list[datetime.datetime ] | list[str] | tuple[str, str] | None ``optional`` Temporal range: upper and lower bounds for temporal subsetting. If ``None``, whole period of input files will be processed. The dates can either be given as instance of datetime.datetime or as string values. For strings, many format are accepted. Default is ``None``. out_file: str | None Output NetCDF file name (default: "" in the current directory). Default is "". If the input ``in_files`` is a ``Dataset``, ``out_file`` field is ignored. Use the function returned value instead to retrieve the computed value. If ``out_file`` already exists, icclim will overwrite it! threshold: float | list[float] | None ``optional`` User defined threshold for certain indices. Default depend on the index, see their individual definition. When a list of threshold is provided, the index will be computed for each thresholds. transfer_limit_Mbytes: float Deprecated, does not have any effect. callback: Callable[[int], None] ``optional`` Progress bar printing. If ``None``, progress bar will not be printed. callback_percentage_start_value: int ``optional`` Initial value of percentage of the progress bar (default: 0). callback_percentage_total: int ``optional`` Total percentage value (default: 100). base_period_time_range: list[datetime.datetime ] | list[str] | tuple[str, str] | None ``optional`` Temporal range of the reference period. The dates can either be given as instance of datetime.datetime or as string values. It is used either: #. to compute percentiles if threshold is filled. When missing, the studied period is used to compute percentiles. The study period is either the dataset filtered by `time_range` or the whole dataset if `time_range` is missing. For day of year percentiles (doy_per), on extreme percentiles the overlapping period between `base_period_time_range` and the study period is bootstrapped. #. to compute a reference period for indices such as difference_of_mean (a.k.a anomaly) if a single variable is given in input. doy_window_width: int ``optional`` Window width used to aggreagte day of year values when computing day of year percentiles (doy_per) Default: 5 (5 days). min_spell_length: int ``optional`` Minimum spell duration to be taken into account when computing the sum_of_spell_lengths. rolling_window_width: int ``optional`` Window width of the rolling window for indicators such as `{max_of_rolling_sum, max_of_rolling_average, min_of_rolling_sum, min_of_rolling_average}` only_leap_years: bool ``optional`` Option for February 29th (default: False). ignore_Feb29th: bool ``optional`` Ignoring or not February 29th (default: False). interpolation: str | QuantileInterpolation | None ``optional`` Interpolation method to compute percentile values: ``{"linear", "median_unbiased"}`` Default is "median_unbiased", a.k.a type 8 or method 8. Ignored for non percentile based indices. out_unit: str | None ``optional`` Output unit for certain indices: "days" or "%" (default: "days"). netcdf_version: str | NetcdfVersion ``optional`` NetCDF version to create (default: "NETCDF3_CLASSIC"). user_index: UserIndexDict ``optional`` A dictionary with parameters for user defined index. See :ref:`Custom indices`. Ignored for ECA&D indices. save_thresholds: bool ``optional`` True if the thresholds should be saved within the resulting netcdf file (default: False). date_event: bool When True the date of the event (such as when a maximum is reached) will be stored in coordinates variables. **warning** This option may significantly slow down computation. logs_verbosity: str | Verbosity ``optional`` Configure how verbose icclim is. Possible values: ``{"LOW", "HIGH", "SILENT"}`` (default: "LOW") sampling_method: str Choose whether the output sampling configured in `slice_mode` is a `groupby` operation or a `resample` operation (as per xarray definitions). Possible values: ``{"groupby", "resample", "groupby_ref_and_resample_study"}`` (default: "resample") `groupby_ref_and_resample_study` may only be used when computing the `difference_of_means` (a.k.a the anomaly). indice_name: str | None DEPRECATED, use index_name instead. user_indice: dict | None DEPRECATED, use user_index instead. window_width: int DEPRECATED, use doy_window_width, min_spell_length or rolling_window_width instead. save_percentile: bool DEPRECATED, use save_thresholds instead. """ # noqa: E501 _setup(callback, callback_percentage_start_value, logs_verbosity) ( index_name, user_index, save_thresholds, doy_window_width, ) = _handle_deprecated_params( index_name, user_index, save_thresholds, doy_window_width, indice_name, transfer_limit_Mbytes, user_indice, save_percentile, window_width, ) del indice_name, transfer_limit_Mbytes, user_indice, save_percentile, window_width # -- Choose index to compute interpolation = QuantileInterpolationRegistry.lookup(interpolation) indicator: Indicator standard_index: StandardIndex | None logical_link: LogicalLink coef: float | None build_configured_threshold = partial( _build_threshold, doy_window_width=doy_window_width, base_period_time_range=base_period_time_range, only_leap_years=only_leap_years, interpolation=interpolation, ) if user_index is not None: standard_index = None indicator = read_indicator(user_index) if threshold is None: threshold = read_thresholds(user_index, build_configured_threshold) logical_link = read_logical_link(user_index) coef = read_coef(user_index) date_event = read_date_event(user_index) rename = index_name or user_index.get("index_name", None) or "user_index" output_unit = out_unit rolling_window_width = user_index.get("window_width", rolling_window_width) base_period_time_range = user_index.get( "ref_time_range", base_period_time_range, ) elif index_name is not None: # TODO @bzah: [BoundedThreshold] read logical_link from threshold instead # logical_link = LogicalLinkRegistry.LOGICAL_AND coef = None standard_index = EcadIndexRegistry.lookup(index_name, no_error=True) if standard_index is None: indicator = GenericIndicatorRegistry.lookup(index_name) rename = None output_unit = out_unit else: indicator = standard_index.indicator threshold = standard_index.threshold rename = standard_index.short_name output_unit = out_unit or standard_index.output_unit else: msg = ( "You must fill either index_name or user_index" "to compute a climate index." ) raise InvalidIcclimArgumentError(msg) sampling_frequency = FrequencyRegistry.lookup(slice_mode) if isinstance(threshold, str): threshold = build_configured_threshold(threshold) elif isinstance(threshold, Sequence): threshold = [build_configured_threshold(t) for t in threshold] climate_vars_dict = read_in_files( in_files=in_files, var_names=var_name, threshold=threshold, standard_index=standard_index, ) # We use groupby instead of resample when there is a single variable that must be # compared to its reference period values. is_compared_to_reference = _must_add_reference_var( climate_vars_dict, base_period_time_range, ) indicator_name = ( standard_index.short_name if standard_index is not None else ) climate_vars = build_climate_vars( climate_vars_dict=climate_vars_dict, ignore_Feb29th=ignore_Feb29th, time_range=time_range, base_period=base_period_time_range, standard_index=standard_index, is_compared_to_reference=is_compared_to_reference, ) if base_period_time_range is not None: reference_period = tuple( (read_date(t).strftime("%m-%d-%Y") for t in base_period_time_range), ) else: reference_period = None config = IndexConfig( save_thresholds=save_thresholds, frequency=sampling_frequency, climate_variables=climate_vars, min_spell_length=min_spell_length, rolling_window_width=rolling_window_width, out_unit=output_unit, netcdf_version=NetcdfVersionRegistry.lookup(netcdf_version), interpolation=interpolation, callback=callback, is_compared_to_reference=is_compared_to_reference, reference_period=reference_period, indicator_name=indicator_name, logical_link=logical_link, coef=coef, date_event=date_event, sampling_method=sampling_method, ) result_ds = _compute_climate_index( climate_index=indicator, config=config, initial_history=climate_vars[0].global_metadata["history"], initial_source=climate_vars[0].global_metadata["source"], rename=rename, reference=standard_index.reference if standard_index is not None else ICCLIM_REFERENCE, ) if out_file is not None: _write_output_file( result_ds, climate_vars[0].global_metadata["time_encoding"], config.netcdf_version, out_file, ) callback(callback_percentage_total) log.ending_message(time.process_time()) return result_ds
def _write_output_file( result_ds: xr.Dataset, input_time_encoding: dict | None, netcdf_version: NetcdfVersion, file_path: str, ) -> None: """Write `result_ds` to a netCDF file on `out_file` path.""" if input_time_encoding: time_encoding = { "calendar": input_time_encoding.get("calendar"), UNITS_KEY: input_time_encoding.get(UNITS_KEY), "dtype": input_time_encoding.get("dtype"), } else: time_encoding = {UNITS_KEY: "days since 1850-1-1"} result_ds.to_netcdf( file_path,, encoding={"time": time_encoding}, ) def _handle_deprecated_params( index_name, user_index, save_thresholds, doy_window_width, indice_name, transfer_limit_Mbytes, # noqa: N803 user_indice, save_percentile, window_width, ) -> tuple[str, UserIndexDict, bool, int]: if indice_name is not None: log.deprecation_warning(old="indice_name", new="index_name") index_name = indice_name if user_indice is not None: log.deprecation_warning(old="user_indice", new="user_index") user_index = user_indice if transfer_limit_Mbytes is not None: log.deprecation_warning(old="transfer_limit_Mbytes") if save_percentile is not None: log.deprecation_warning(old="save_percentile", new="save_thresholds") save_thresholds = save_percentile if window_width is not None: log.deprecation_warning(old="window_width", new="doy_window_width") doy_window_width = window_width return index_name, user_index, save_thresholds, doy_window_width def _setup(callback, callback_start_value, logs_verbosity) -> None: # make xclim input daily check a warning instead of an error # TODO @bzah: it might be safer to feed a context manager which will setup # and teardown these confs # xclim.set_options(data_validation="warn") # keep attributes through xarray operations xr.set_options(keep_attrs=True) log.set_verbosity(logs_verbosity) log.start_message() callback(callback_start_value) def _get_unit(output_unit: str | None, da: DataArray) -> str | None: da_unit = da.attrs.get(UNITS_KEY, None) if da_unit is None: if output_unit is None: warn( "No unit computed or provided for the index was found." " Use out_unit parameter to add one.", stacklevel=2, ) return "" return output_unit return da_unit def _compute_climate_index( climate_index: Indicator | None, config: IndexConfig, initial_history: str | None, initial_source: str, reference: str, rename: str | None = None, ) -> Dataset: result_da = climate_index(config) if rename: result_da = result_da.rename(rename) else: result_da = result_da.rename( result_da.attrs[UNITS_KEY] = _get_unit(config.out_unit, result_da) if ( config.frequency.post_processing is not None and "time" in result_da.dims and not isinstance( climate_index, ( XclimBinding.StandardizedPrecipitationIndex6, XclimBinding.StandardizedPrecipitationIndex3, ), ) ): resampled_da, time_bounds = config.frequency.post_processing(result_da) result_ds = resampled_da.to_dataset() if time_bounds is not None: result_ds["time_bounds"] = time_bounds result_ds.time.attrs["bounds"] = "time_bounds" else: result_ds = result_da.to_dataset() if config.save_thresholds: result_ds = xr.merge( [result_ds, _format_thresholds_for_export(config.climate_variables)], ) history = _build_history(result_da, config, initial_history, climate_index) return _add_ecad_index_metadata( result_ds, climate_index, history, initial_source, reference, ) def _add_ecad_index_metadata( result_ds: Dataset, computed_index: Indicator, history: str, initial_source: str, reference: str, ) -> Dataset: result_ds.attrs.update( { "title": computed_index.standard_name, "references": reference, "institution": "Climate impact portal (", "history": history, "source": initial_source if initial_source is not None else "", "Conventions": "CF-1.6", }, ) try:["_FillValue"] = None result_ds.lon.encoding["_FillValue"] = None except AttributeError: try: result_ds.latitude.encoding["_FillValue"] = None result_ds.longitude.encoding["_FillValue"] = None except AttributeError: pass return result_ds def _build_history( result_da: DataArray, config: IndexConfig, initial_history: str | None, indice_computed: Indicator, ) -> str: from icclim import __version__ as icclim_version if initial_history is None: # get xclim history initial_history = result_da.attrs[HISTORY_CF_KEY] else: # append xclim history initial_history = f"{initial_history}\n{result_da.attrs[HISTORY_CF_KEY]}" del result_da.attrs[HISTORY_CF_KEY] current_time = "%Y-%m-%d %H:%M:%S", ) return ( f"{initial_history}\n" f" [{current_time}]" f" Calculation of {}" f" index ({config.frequency.adjective})" f" - icclim version: {icclim_version}" ) def _build_threshold( threshold: str | Threshold, doy_window_width: int, base_period_time_range: Sequence[dt.datetime | str] | None, only_leap_years: bool, interpolation: QuantileInterpolation, ) -> Threshold: if isinstance(threshold, Threshold): return threshold return build_threshold( threshold, doy_window_width=doy_window_width, reference_period=base_period_time_range, only_leap_years=only_leap_years, interpolation=interpolation, ) def _format_thresholds_for_export(climate_vars: list[ClimateVariable]) -> Dataset: return xr.merge([_format_threshold(v) for v in climate_vars]) def _format_threshold(cf_var: ClimateVariable) -> DataArray: return cf_var.threshold.value.rename( + "_thresholds").reindex() # TODO @bzah: move `read_indicator`, `read_threshold`, `read_logical_link`, `read_coef`, # `read_date_event` to a user_index_parsing module # def read_indicator(user_index: UserIndexDict) -> GenericIndicator: calc_op = CalcOperationRegistry.lookup(user_index["calc_operation"]) user_index_map = { CalcOperationRegistry.MAX: GenericIndicatorRegistry.lookup("Maximum"), CalcOperationRegistry.MIN: GenericIndicatorRegistry.lookup("Minimum"), CalcOperationRegistry.SUM: GenericIndicatorRegistry.lookup("Sum"), CalcOperationRegistry.MEAN: GenericIndicatorRegistry.lookup("Average"), CalcOperationRegistry.EVENT_COUNT: GenericIndicatorRegistry.lookup( "CountOccurrences", ), CalcOperationRegistry.MAX_NUMBER_OF_CONSECUTIVE_EVENTS: GenericIndicatorRegistry.lookup( # noqa: E501 "MaxConsecutiveOccurrence", ), CalcOperationRegistry.ANOMALY: GenericIndicatorRegistry.lookup( "DifferenceOfMeans", ), } if calc_op == CalcOperationRegistry.RUN_SUM: if user_index["extreme_mode"] == "max": indicator = GenericIndicatorRegistry.lookup("MaxOfRollingSum") elif user_index["extreme_mode"] == "min": indicator = GenericIndicatorRegistry.lookup("MinOfRollingSum") else: raise NotImplementedError elif calc_op == CalcOperationRegistry.RUN_MEAN: if user_index["extreme_mode"] == "max": indicator = GenericIndicatorRegistry.lookup("MaxOfRollingAverage") elif user_index["extreme_mode"] == "min": indicator = GenericIndicatorRegistry.lookup("MinOfRollingAverage") else: raise NotImplementedError else: indicator = user_index_map.get(calc_op) if indicator is None: msg = f"Unknown user_index calc_operation: '{user_index['calc_operation']}'" raise InvalidIcclimArgumentError(msg) return indicator def read_thresholds( user_index: UserIndexDict, _build_threshold: Callable[[str | Threshold], Threshold], ) -> Threshold | None | Sequence[Threshold]: thresh = user_index.get("thresh", None) if thresh is None or isinstance(thresh, Threshold): return thresh # TODO @bzah: [BoundedThreshold] read bounded threshold if thresh is a Sequence # logical_operation = user_index["logical_operation"] if not isinstance(logical_operation, (tuple, list)): logical_operation = [logical_operation] logical_operations = [OperatorRegistry.lookup(op) for op in logical_operation] var_type = user_index.get("var_type", None) if not isinstance(thresh, (tuple, list)): return read_threshold(thresh, var_type, logical_operations[0], _build_threshold) return [ read_threshold(t, var_type, logical_operations[i], _build_threshold) for i, t in enumerate(thresh) ] def read_threshold( query: str | float, var_type: Literal["t", "p"] | None, logical_operation: Operator, _build_threshold: Callable[[str], Threshold], ) -> Threshold: if isinstance(query, str) and query.endswith(PERCENTILE_THRESHOLD_STAMP): if var_type == USER_INDEX_TEMPERATURE_STAMP: replace_unit = "doy_per" elif var_type == USER_INDEX_PRECIPITATION_STAMP: replace_unit = "period_per" else: replace_unit = "period_per" # default to period percentiles ? t = query.replace(PERCENTILE_THRESHOLD_STAMP, " " + replace_unit) else: t = str(query) return _build_threshold(str(logical_operation.operand + t)) def read_logical_link(user_index: UserIndexDict) -> LogicalLink: # TODO @bzah: add unit test using it # logical_link = user_index.get("link_logical_operations", None) if logical_link is None: return LogicalLinkRegistry.LOGICAL_AND return LogicalLinkRegistry.lookup(logical_link) def read_coef(user_index: UserIndexDict) -> float | None: # TODO @bzah: add unit test using it # return user_index.get("coef", None) def read_date_event(user_index: UserIndexDict) -> float | None: # TODO @bzah: add unit test using it # return user_index.get("date_event", False) def _must_add_reference_var( climate_vars_dict: dict[str, InFileDictionary], reference_period: Sequence[str] | None, ) -> bool: """True whenever the input has no threshold and only one studied variable but there is a reference period. Example case: the anomaly of tx(1960-2100) by tx(1960-1990). """ t = next(iter(climate_vars_dict.values())).get("thresholds", None) return t is None and len(climate_vars_dict) == 1 and reference_period is not None