Search site


Precipitation refers to any atmospheric water vapour that falls to earth under gravity. This includes rain, hail and snowfall.

In detail

Projections of rain, snow and hail are not individually included in UKCP09. The probabilistic projections of change in precipitation rate are a total of precipitation of all types.

  • Rain is liquid precipitation that falls as water.
  • Hail is solid precipitation that consists of small irregular lumps of ice.
  • Snow is a type of precipitation that falls in the form of small ice particles.

For UKCP09, creating probabilistic projections of changes in snowfall rate was not possible because the models sometimes project small but non-zero values in the future, implying changes relative to the baseline climate that are close to the absolute lower bound of -100%. Under these conditions, statistical contributions to the uncertainties captured in the UKCP09 methodology were found to become unrealistically large, and hence probabilistic projections were not provided.

In the absence of a UKCP09 probabilistic projection for snowfall rate, there are three possible alternative sources of projections of transient changes during the 21st century:

  • The 17-member ensemble of variants of the Met Office GCM
  • The 11-member ensemble of variants of the Met Office RCM
  • The ensemble of other global climate models, available as part of the CMIP3 project

Data from the first two (Met Office GCM and RCM) is available from the Climate Impacts LINK project, operated by . In the case of snowfall rate, the use of changes from the 11-member Met Office RCM ensemble is recommended in the first instance.

Find out more


  • For variables for which probabilistic projections could not be provided, go to Chapter 5 of the UKCP09 Briefing Report. More details are provided in the UKCP09 Climate Change Projections report.
  • More details about the climate models used are given in Box 2.1 of the UKCP09 Climate Change Projections report. A commentary about the strengths and weaknesses of climate models is given in Annex 3.
  • For an overview of how probabilistic projections are created and presented, see Box 3 of the UKCP09 Briefing Report. More details are in Chapter 3 of the UKCP09 Climate Change Projections report, including an overview of the methodology.
  • Recent trends in wind speed are presented in Chapter 2 of the Observed Trends report.