Ireland’s Climatological Standard Normals (CLINO) 1991-202

Abstract

Climatological Standard Normals (CLINO) are the mean or average values of a climate variable over a standard reference period. The World Meteorological Organization (WMO) established that the length of the reference period should be 30 years, with a recommendation to update the climate normals every 10 years, to provide representative reference values for recent climatic conditions. Climate normals are used for two principal purposes. They serve as a benchmark against which recent or current observations can be compared, including providing a basis for many anomaly-based climate datasets. They are also widely used as a reference baseline to provide context for future climate projections.By applying the WMO data requirements and criteria, Met Éireann has compiled a set of climate normals for the period 1991-2020 for a range of parameters including temperature, precipitation, solar radiation, wind and pressure. Annual, seasonal, and monthly normal values for the period 1991-2020 were compiled using quality assured data obtained from Met Éireann’s observation network. Values are averaged for each month over the 30-year period to obtain the long-term average. Where there are gaps in data, estimates are made using data from neighbouring stations. Long-term averages for stations are then used to generate maps and gridded data at a 1km resolution.A comparison of the most recent 30-year period with the 1961-1990 period shows an increase in annual mean temperature of approximately 0.7°C. All seasons experienced a rise in mean temperatures, with Spring displaying the greatest differences between the two periods.On an annual basis, averaged over the country, there has been an increase of approximately 7% in rainfall totals between the two normal periods (1961-1990 and 1991-2020), with the greatest increases observed in the western half of the country. All seasons show an overall increase in rainfall but there are regional variations.Here we present the data and methods used to produce the latest set of climate normals for Ireland as well as an assessment of trends between the two normal periods, 1961-1990 and 1991-2020.From September 2023, weather and climate statistics will reference the new long-term average period 1991-2020, unless otherwise stated. These will replace the 1981-2010 long-term averages that are currently in use. The historical baseline period of 1961-1990 will be retained for use in climate change assessments.