VARIABILITY AND PREDICTABILITY OF WATER SUPPLY 135 
hydrological research and development now in hand in these 
territories. 
Outline of Situation in British Overseas and Commonwealth Ter- 
ritories 
The points suggested for discussion comprise the following: 
1. How predictable is precipitation in an arid region? 
2. Are there distinct drought cycles? 
3. What are the prospects for usable ground water occurrence 
in arid areas? 
4. What is the practicability of locating and estimating volume 
and rate of natural recharge of underground water supplies? 
5. Within a given watershed, to what degree can the water 
sources and water yield be determined? 
I have considered these points in turn in relation to investiga- 
tion and development now proceeding in various British Overseas 
and Commonwealth Territories. Very brief, general answers are 
given in this paper, detailed answers for each area in a paper 
published separately in Colonial Geology and Mineral Resources. 
I wish here to express my great indebtedness to all those officers 
mentioned in the text who have supplied me with the information 
on which this account is based. 
1. How Predictable 1s Precipitation in an Arid Region? In the 
territories considered precipitation is not ordinarily predictable 
owing to the absence of adequate long-term data on which to base 
statistical investigations. 
2. dre There Distinct Drought Cycles? In the British Overseas 
Territories considered droughts are of common occurrence, but 
they do not recur in regular cycles. 
3. What Are the Prospects for Usable Ground Water Occurrence in 
Arid Areas? In the territories considered, in the most arid areas, 
such as Somaliland, northern Kenya, parts of Tanganyika, and 
Bechuanaland, usable ground waters are found only with diff- 
culty, and the percentage of successful boreholes is low, 50%, or 
less; waters are frequently too saline for use, and in parts of Tan- 
ganyika and Kenya the fluorine content is also high. The waters 
occur at depths of 300 to 400 feet, or even more. In the less arid 
