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Rainfall amounts in the Sahel region of Africa began a decline around 1968 that has continued to the present. The drought of 1982–83 was more severe and devastating than the well-known drought of 1972–73. Most years between 1972 and 1983 experienced below to well-below normal rainfall. These 16 or so dry years make obsolete mean (or normal) rainfall data calculated for periods before the decline began. Despite this, the old normal values are still widely used for various national and international agricultural projects. Discrepancies between the old and new mean values for the amounts of rainfall, and differences in the duration of the rainy season, suggest that mean or normal rainfall data should be calculated for the last 30 and/or 16 years. The rapidly changing climate in the Sahel requires more frequent updating of the climatological normals.
A. V. Todorov (Fri,) studied this question.