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Threshold Detector

The UKCP09 Threshold Detector (TD) is a post-processing tool that can be applied to the output from the Weather Generator (WG), and was developed following guidance from the UKCP09 Users' Panel.

The TD allows users to define their own basic weather events (or indices) made up of simple conditions such as temperatures or daily rainfall totals greater/lower than a certain threshold. The TD then cycles through the WG outputs and counts the number of occurrences of the prescribed event. Along with the counts per WG run, the TD will also produce a set of summary statistics across all the runs. The data can then be downloaded or the summary statistics visualised by the user. For more information see the Threshold Detector User Manual (opens in new window).

It is only possible to use Threshold Detector with Weather Generator output, and only output from daily Weather Generator runs (not hourly), for a 30 year duration, and for 100 samples can be analysed.

Running the TD provides information on the exceedance of the user-defined event. Depending on the nature of the requested event, various information may be available, for the following 17 temporal average periods:

  • Months: January-December (12)
  • Seasons: Winter, Spring, Summer, Autumn (4)
  • Annual (1)
  • A TD job can be viewed in the UKCP09 User Interface (UI), and/or the data can be downloaded. From the UI, the graphic can be saved as: .png, .jpeg, .ps, and .pdf. The data sets can be downloaded in .csv format, and CF-netCDF.
  • What should I use it for?

For identifying events in the Weather Generator output that are of interest

There are three pre-defined events that can be run (, ,and ),and it is also possible to define a custom event. For more information and examples, see the User Manual (opens in new window).

  • Uncertainty

Uncertainty in the Threshold Detector is represented by box and whisker plots, which display the mean, 1 and 2 standard deviations about the mean, and the minimum and maximum recorded number of events.

In the summary statistics data files, uncertainty is represented by reporting the mean, minimum, maximum, standard deviation, and standard error about the event under investigation.

  • What should I be aware of?

The Threshold Detector should not be used to investigate very long duration events

The maximum length of an event permissible in the Threshold Detector is 15 days. For example, droughts are normally defined over much longer time scales, so users looking to investigate droughts will need to process the Weather Generator output themselves. For more information on the limitations of the Threshold Detector, see the Annex of the Weather Generator report.

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