Anomalies

Anomalies#

CLIX offers the functionality to calculate anomalies of climate indicators using the --anomaly option and supports two types of anomaly calculations:

  • Absolute (``abs``): Calculates the absolute differences.

  • Percentage (``perc``): Calculates the percentage differences.

Calculating Anomalies#

To calculate an anomaly, you must provide two distinct time periods using the --date_range and --ref_date_range arguments. This is because anomalies are calculated as the difference between a specific period and a reference (climatological) period. The reference period is always averaged to the given frequency and serves as a climatological reference period (refer to the Climatology documentation).

To calculate time series anomalies, the following example shows the command to get the monthly anomalies of recent summer days compared to the climatological WMO period of 1961-1990.

Example: Time Series of Monthly Absolute Anomalies of Summer Days

This command calculates the monthly absolute anomalies of txge25 (summer days) by comparing the period 2011-2020 against 1961-1990:

clixrun --input /path/to/tas/input/dir/ --date_range 20110101 20201231 --ref_date_range 19610101 19901231 --frequency month --anomaly abs txge25

Example: Time Series of Percentage Anomalies of Total Precipitation Amount

This command calculates the yearly percentage anomalies of total precipitation amount, comparing 1991-2020 with the climatological mean of 1961-1990:

clixrun --input /path/to/precip/input/dir/ --date_range 19910101 20201231 --ref_date_range 19610101 19901231 --frequency year --anomaly perc rtot

To calculate anomalies between two climatological periods, use the --average argument in combination with --anomaly.

Example: Calculate Seasonal Absolute Anomalies of Days with Precipitation Above 20 mm

This command calculates the seasonal absolute anomalies of rgt20mm (days with precipitation above 20 mm) by comparing the period 2071-2100 against 1961-1990, where both periods are averaged before the anomaly calculation:

clixrun --input /path/to/scenario.yaml --date_range 20710101 21001231 --ref_date_range 19610101 19901231 --frequency season --anomaly abs --average rgt20mm