ALTHOUGH we live in a country generously endowed with rainfall, it rains, in fact, much less then one might think. In south west Kerry, for example, one of the wetter parts of Ireland, there are about 850 hours of rain in the average year; this, if you work it out means that it rains for about 10 per cent of the time. Drier parts of the country, such as Dublin and its hinterland, experience about 550 hours per year, which amounts to around 6 per cent of the time.
Sometimes, however, as at present, lengthy periods occur when there is no rain at all, a happening commonly called a drought. The dictionary defines drought as simply "prolonged dry weather" but this, of course, just prompts the questions: "How prolonged?" and "How dry?", and there are no precise answers that can apply everywhere in the world. Rainfall low enough to cause a shortage in one region of the globe, might be regarded as water in abundance in another.
A common criterion is to regard drought as present if living organisms are suffering because of a deficiency in rainfall. But this is a biological definition rather than a meteorological one, and is in any case less than satisfactory because of the complicated and variable relationship between the weather, plants and animals. Moreover, in today's urban society, thoughts of drought are often closely related to the ability of the local water authority to cope with periods of low rainfall, which in turn depends largely on water storage capacity in the region.
Meteorologists in Ireland and Britain use rather arbitrary and somewhat confusing terms to classify periods when water is in short supply. A dry spell is defined as a period of 15 or more consecutive days with less then 1 mm of rainfall on each; and absolute drought is a period of 15 or more consecutive days with less than 0.2 mm on each; and a partial drought is a period of at least 29 consecutive days with a rainfall total averaging less than 0.2 mm of rain per day. With this terminology, somewhat, paradoxically in the context of their names, absolute droughts are more frequent than partial droughts.
A dry spell occurs in Ireland most years, and sometimes more than once. An absolute drought occurs about one year in three, and partial droughts come along only about one year in 10. And if there is no significant rain before midnight tonight - a very likely eventuality, looking at the weather charts - most of the southern half of Ireland will have entered into the realm of absolute drought.