Science: Drought comes hand in hand with rain

日期:2019-02-26 08:20:01 作者:郜瞑灞 阅读:

THIS YEAR’S drought in southern England may be part of a change in climate which made the 1980s the wettest decade ever in Britain as a whole. If the pattern persists, Britain can expect plenty of winter rainfall. In the 19th century, almost the same amount of rain fell in summer as in winter, but in the 1980s, winters were three times as wet as summers. Terry Marsh, of the Institute of Hydrology, and Richard Monkhouse, of the British Geological Survey (both based in Wallingford) have obtained these figures while investigating the hydrological aspects of the 1989 drought (Weather, vol 45, p 290). Winter rainfall in Scotland, they point out, ‘has been especially remarkable’ – 8 of the 12 wettest winters in a series extending back to 1869 have occurred since 1979. The British drought in 1989 was broken by heavy winter rainfall in southern England, as well as further north. Over Great Britain as a whole, the rainfall in February 1990 was the highest for any February back to 1869, while for England and Wales it was the second wettest February (after 1977) for the past 40 years. Interestingly, the heavy rains of the winter of 1976 to 1977 also followed summer drought. For the whole winter (December-February) of 1989 to 1990, rainfall totals for Britain were second only to those of 1914 to 1915 in the record of the 20th century. Marsh and Monkhouse do not offer any explanation for the extreme climatic events of the 1980s. The pattern they describe does, however, fit some of the predictions of changes associated with global warming caused by the greenhouse effect. Summer droughts are an obvious consequence of higher temperatures, especially in continental interiors; but warmer ocean waters provide, by evaporation, the moisture for potential increases in rainfall. In Britain, with prevailing winds off the Atlantic, any extra rain would indeed fall to the north and west of the country, while incursions of ‘continental’ warmer weather would give the southeast the opportunity to experience hot,