What to use it for
The Weather Generator (WG) provides a useful extension to the UKCP09 projections, particularly when there is a need to:
- Investigate local scale impacts in detail
- Explore the likelihood of some types of extreme events
- Investigate the risk of thresholds being exceeded
See the UKCP09 Reports & guidance for a comprehensive overview of how the WG works and how the output should be used.
The WG provides weather time series at daily or hourly time steps and at a spatial resolution of 5 km (or if an area is selected, for an area up to 1,000 km2).
The UKCP09 WG is a 'stochastic' simulator. It produces 100 equally-plausible simulations of 30 years of daily time series for the baseline period and a minimum of 100 30 year time series for a future time period*. Users should not average the outputs from the generated time series to produce a single time series.
*There are 10,000 model variants in the UKCP09 probabilistic projections that can be used to generate future time series. The WG can be used to explore a specific portion of these (generating up to 1,000 individual time series at a time).
Explore the likelihood of some types of extreme events
The UKCP09 weather generator can be used to generate long time series (user-specified of up to 1000 years) that are statistically consistent with a particular climate.
This capability can be useful where the recurrence interval of particular events is of interest. For example, the weather generator output can be analysed to examine the recurrence frequency of certain daily rainfall totals.
Extreme statistics for return periods greater than 10 years based on the daily time series should be treated with caution, because the WG is trained on a relatively short record. Users are advised to carry out uncertainty analysis using all 100 of the Weather Generated series generated. Hourly extreme statistics are subject to greater uncertainty, and return periods beyond 5 years should be used with caution.
The weather time series generated by the WG can be used to analyse the frequency of certain thresholds being exceeded. For example, the weather generator output can be analysed to examine the risk of daily maximum temperature exceeding a specific temperature (e.g. 30°C). The UKCP09 Threshold Detector (TD) is a post-processing tool that can be applied to the output from the WG to aid this process.