THE MODIFICATION OF SOUTH AFRICAN 

 RAINFALL. 



By John M. Sim. 



\\ ilh the semi-arid conditions pertaining to-day in Sovitli 

 Africa, one of the most serious questions we have to face is the 

 question of the continuance of the water supply. Already we 

 have to accept the fact that a large portion of South Africa has 

 an entirely inadequate water supply, that the water supply of a 

 further portion is threatened by the spread of desiccating con- 

 ditions, and that even (Ui those regions on which the rainfall 

 as yet can be said to l)e sufficient desiccation is proceeding, the 

 ultimate effect of which must Ije in time the conversion of them 

 into arid or semi-arid localities. For both historically and 

 scientifically it is an established fact that for the last two 

 hundred vears or more there has been a steady and ])ersistent 

 decrease in the rainfall, and an e(|ually steady change in the 

 character of it. The result we see to-day in the conversion of 

 many parts of South Africa into what may almost be designated 

 as desert. With these desert conditions extending, the whole 

 productiveness of the country is threatened. 



I would commence by briefly enumerating some of the 

 more important proofs of the continued desiccation of Soiuh 

 Africa. These i)roofs I would divide into two classes: firstly, 

 those which may rightly be called historical proofs, and those 

 wdiich are forced on us by natural facts. Both are convincing. 

 but since w'ritten proofs are mostly to be obtained from prcx-la- 

 mations and writings ha\'ing ]irimary reference to some other 

 subject, the natural proofs must be taken in conjunction with 

 them to entirely estal)lish their ])oint. 



Jdistorically, we have no proof at all of the hydnjlogical 

 conditions existing in .South .\frica prior to the advent of the 

 Netherlands East India Company in 1652. Even after the com- 

 ing of the Dutch our proof lies in the ])roclamations they issued 

 mainly in the relation to timber-felling and grass-burning, and 

 not in any direct reference to the rainfall. But such facts as 

 the following allow us to deduce hydrological conditions ver\- 

 ditTerent from those of the present time: 



.\bout 100 placaals issued between the years 1652 and i(So6 

 relate to the gcnernmcnt of the f(^rcsts of the Western I'rovince 

 of Cape Colony. I-'rom these it is evident that extensi\e forests 

 existed not merely in the vicinity of Cai)e Town, but also as 

 far U[) the coast as .Saldanha Bay. References to the cutting of 

 yellowwood at .Stellenboscli and Swellendam denote the presence 

 of forests ^)f .some extent at these places. The Cedarberg was 

 crowned by forests of Clanwilliam cedar. Xow our indigaious 

 forests are moisture-loving fc^rests. and the presence of these 

 forests in practically a continuous belt from Ca])e Town to 



