METEOROLOGY II5 



especially in 1898, 1908, 191 8-19, and 1928, appear to be similarly- 

 periodic, and are essentially due to failure of the short rains in the 

 preceding year. 



Though the relation between rainfall, lake levels, and sunspots 

 might seem to be of academic interest, these examples suggest 

 that full understanding of climatic cycles in Africa may eventually 

 lead to long-range weather forecasting of sufficient accuracy to be 

 of real economic value. 



ALLEGED PROGRESSIVE DESICCATION 



Some authorities believe that the whole continent of Africa is 

 affected by a progressive desiccation, which is said to have been 

 accelerated in recent years. There is an extensive literature on the 

 subject, particularly in relation to West and South Africa. Colonel 

 Tilho is the authority for the Chad Basin, and M. Hubert for the 

 Senegal region. The late Professor Schwarz discussed the problem 

 as affecting Africa as a whole, but it should be noted that some of 

 his conclusions have been discredited as a result of more recent 

 work. The evidence strongly suggests that large tracts of Africa 

 are drying up, through a combination of influences, geographical, 

 meteorological, and human. 



The chief geographical factor is river-capture, though the silting 

 up of streams and lakes and the movement of sand dunes have also 

 played their part. Schwarz ( 1 92 1 ) laid great stress on the unfavour- 

 able topography of Africa, which is such as to give rise to steady 

 head-stream erosion by short coastal rivers, resulting in the capture 

 of water which formerly drained the interior of the continent. He 

 considered this the fundamental cause of the disappearance of 

 Lake Ngami in the Kalahari, and of the dwindling of Lake Chad, 

 as well as of a great diminution in the volume of the Niger in 

 modern tim.es. He suggested also that the ultimate fate of Lake 

 Victoria will be capture by an affluent stream of Lake Tanganyika, 

 which is cutting back the low watershed to the south-west of Lake 

 Victoria. A thorough examination of the area, however, has 

 shown that this cannot happen for many thousands, if not millions, 

 of years. Colonel Tilho (1928) fears that Lake Chad may dis- 

 appear through the capture of the Logone and ultimately of the 



