Historical and modern fluctuations of Lakes Tanganyika and Rukwa and theirrelationship to rainfall variability

This paper describes the fluctuations of Lakes Tanganyika and Rukwa over th e last two centuries. Lake chronologies extending back to the late eighteen th century are derived from reports of European visitors, settlers and expl orers and from oral accounts of the local peoples. The historical fluctuations are meshed with the modern record to provide a picture of the lakes' fluctuations until the late twentieth century. The hi storical fluctuations of the lakes are quire similar. The most important of these are low levels during the first half of the nineteenth century, very high stands in the last decades of the nineteenth century, and, around the turn of the century, a rapid fall to twentieth century levels. This patter n is ubiquitous throughout eastern Africa and is apparent in numerous other lakes, including Victoria, Naivasha, Stefanie, Turkana, Malawi and Chilwa. Driest periods were in the 1920s or earlier and in the 1950s. Lake Tangany ika returned to extremely high stands in the 1960s and has continued to mai ntain relatively high stands since that time. Lake Rukwa rose to high stand s during the 1980s and maintained them for several years. An analysis of rainfall variability shows that these trends are generally e xplained by variations in catchment rainfall. However, the lakes' responses to rainfall variability are sometimes dissimilar because Lake Rukwa is a c losed basin. Our results demonstrate the complexity of the rainfall/lake-le vel relationships and the need to use water balance relationships in order to interpret the lakes' historical or paleo-fluctuations in terms of rainfa ll.