A 305-year continuous monthly rainfall series for the Island of Ireland (1711-2016)
On 19th June 2018 the Irish Meteorological Society hosted its last lecture of the 2017/18 season. Dr. Conor Murphy of the Irish Climate Analysis and Research Unit (ICARUS) in the Department of Geography in Maynooth University, gave a talk about work that was done to produce a 305-year continuous monthly rainfall series for the island of Ireland.
Dr. Murphy, with colleagues from Maynooth University, Met Éireann, the Met Office in the UK, and many universities, institutions and centres in the UK and Austria, worked together to compile and analyse the continuous monthly rainfall series for the period 1711-2016. A UK Met Office document from 1979 was rediscovered in a refurbishment of Met Éireann in recent years. That document provides a continuous monthly rainfall series for the island of Ireland from 1711 to 1977 based on weather diaries and early observations. The rainfall data from 1711 to 1977 were merged with a homogenised monthly rainfall network for Ireland for a 160-year period from 1850 to 2010 (published in 2016 by Simon Noone from Maynooth University and colleagues) to give a rainfall series of over 300 years.
Dr. Murphy spoke of the challenges that come with developing a reliable, precipitation series over three centuries. Precipitation in solid form, like snow, or liquid form such as rain requires careful measurement. There have been changes over time to the way that weather observers take these measurements, with measurement of snow being a particular challenge and snowfall measurement often being under-measured. The design of rain gauges was in its infancy in the 1700s and 1800s. One gauge in particular was noted as being 12 inches in diameter and located on the ridge of an observer’s house. Rainfall varies widely from one place to another so it is important for rain gauges to have a similar design and exposure to allow comparison of rainfall measurements. In the mid-1800s George J Symons pioneered the standardisation of rain gauges. Today, the World Meteorological Organisation provides guidelines on the siting, location and design of rain gauges.
In this paper by Murphy et al., insights into the long-term rainfall patterns of Ireland can be gleamed. For example, it shows that the most recent decade (2006-2015) was the wettest in over 300 years. The 1850-2010 study also showed that long droughts often occurred in the 1800s.
By Sinéad Duffy, EMS Liaison Committee