natural disasters: Africa 761 Cyclones of Africa In the summer in southern Africa there is a threat of violent tropical storms These are cyclones, also often called hurricanes or typhoons They develop winds of more than 80 miles per hour and can generate tall ocean swells that become storm surges when they break across a coastline These surges can be very destructive, overwhelming houses, people, and animals In addition, the cyclones can sometimes drop enormous amounts of water inland, causing rivers to swell into lakes Sometimes the cyclones sweep from east to west across the continent to Angola A challenge to the medieval peoples of southern Africa was to anticipate the worst storms and to prepare for them An insidious aspect of the storms was that the worst ones did not occur every year Often, storms formed in the east, hit Madagascar, and then weakened and often turned toward the sea Perhaps unaware of the danger, farmers would move into lowlands and could prosper during years when the worst storms did not come In the lower reaches of the Zambezi River, this seems to have been common, but it took only one severe cyclone to swell Lake Malawi, sending torrents down the Zambezi to cause the lower reaches of the Zambezi to swell outward, its channels unable to carry the load of water, flooding the land There were people who began their settlements with a few mud houses covered with thatch, and the settlements developed into cities and towns on the east coast Although many of their buildings were made of stone, most people still lived in traditional houses even at the height of the cities’ prosperity in the 1300s and 1400s Most of these cities were in low-lying areas, thus making them very vulnerable to storm surges How did the peoples of the cities avoid being swept away? An answer may come from the work of archaeologists who have uncovered walls made of massive stones These were likely to have been storm walls, intended to fend off surging water corded in the mid-19th century tells the story of the king of France who waged a war of revenge on Tunis in northern Africa during a period of severe drought in Africa sometime between 1250 and 1270 The frequency with which drought mythologies occupy the African folklore and tradition is not the only evidence supporting the natural occurrence of drought on the continent Nile flow records and the analysis of sediments in African lakes also indicate dry and wet periods However, the picture is no less fragmented from these data sources, which often suggest a great variability in drought and flood conditions The major climatic event of this period was the Medieval Warm Period (approximately 800 through 1300) Climatic conditions in general were dry during this period in Africa, but many factors created variations in local conditions of drought and flood throughout Africa Records from the Nile and elsewhere for the period from 970 through 1500 indicate fluctuations in the seasonal flood levels Some scientists have concluded that the Nile flow data indicate lower general flood levels during the Little Ice Age, approximately 1300 through 1850, compared with the Medieval Warm Period Some of the most extreme conditions occurred during the Medieval Warm Period, which caused severe famines There is evidence of a series of great floods in the Nile River valley in the early ninth century Nile flow records also indicate low average flood levels between the seventh and 15th centuries, with particularly low flood levels in 967, which would certainly have lowered agricultural productivity, creating famine The variation in local drought conditions is so great that droughts that were detected around Lake Naivasha in Kenya in the late 14th and early 15th centuries (which occurred within the 1270–1850 period of generally increased moisture) were not detected around Lake Hayk in northern Ethiopia, although both regions are in East Africa Other climatic data suggest a pattern of increased moisture for eastern Africa near the equator and a pattern of drought in central equatorial Africa during the Little Ice Age Although reasons for the demise of the civilization of Great Zimbabwe (11th through 15th centuries) in southern Africa is unknown, many researchers theorize that it was as least partially due to severe drought These climatic changes did not necessarily result in disaster for the human populations living in these areas Throughout Africa’s history humans have adapted to the ever-changing environmental conditions by altering livelihood strategies and migrating One notable example of adaptation to environmental conditions comes from the Nile Valley The seasonal flooding of the Nile River, which brought water and fertile soil deposits to the valley, was the lifeline of the population rather than the curse Disaster followed if the Nile flood levels were lower than anticipated Low flood levels meant less water for irrigated agriculture and a higher sediment load in the floodwaters, which hindered the flow of water through the irrigation canal systems Therefore, if the