Driving Rain Index for Republic of Ireland. This led Lacy and Shellard to propose the product of the mean annual rainfall and the mean annual wind speed as a driving rain index which is proportional to the total rainfall driven in one year on to a vertical surface always facing the wind. The amount of rain received by a wall correlates fairly well with the product of rainfall and the component of the wind speed normal to the wall. During prolonged spells of wind-driven rain, brickwork and concrete may become saturated and rain may penetrate cracks in a structure or gaps around windows. In such conditions, a vertical wall facing into the wind will receive more precipitation than a horizontal surface of equal area. When a wind is blowing, the drops are also carried along horizontally and with strong winds deflections of more than 45 degrees from the vertical can occur, even for large drops. In calm conditions, raindrops fall vertically with a velocity that depends on their size. However, there is variation between sites of course, for example at stations on higher ground (that is, highest in counties Kerry and Wicklow), rainfall is recorded every one in 3.5 to 4 hours.
For example, the general impression is that it rains quite a lot of the time in Ireland, but only one out of five hourly observations will report measurable rainfall. From this observational dataset, and others, analysis is completed to give details of the Rainfall Climate of Ireland. Since then the network has expanded further, there are now just under 500 rain gauge locations in the country.įrom these rain gauges, Met Éireann has recorded and stored nearly 9.5 million individual hourly rainfall measurements into the National Climate Database between 19. By the early 20th century there were over 100 locations measuring rainfall, by the time the Irish Meteorological Service was formed in 1936 the number of rain gauges was over 200. From the mid 19th century the number of stations increased and some standardisation of observations took places in line with international developments. In the first half of the 19th century readings were taken at Birr Castle (1845), Markree Castle (1824), the Phoenix Park (1829) and Trinity College, Dublin (1838). The history of organised weather observations in Ireland goes back to the late 1700s with Observatories in Dunsink (1787) and Armagh (1790). Historical observations are of particular value since an observation once made in time cannot be retaken, and if observations are not taken we have no way of directly knowing what the past weather and climate were like. The value of high quality observations to the meteorological and climatological scientific communities cannot be overstated.
Rainfall is a key indicator of changes in the climate, measurements and analysis of rainfall are essential for assessing the affects of climate change on the water cycle, water balance and for flood mitigation. Peer-reviewed journal articles by Met Éireann staff members Past Weather Agrometeorological Bulletins
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