202 THE FUTURE OF ARID LANDS 
Figure 2. The Jaguaribe River by the town of the same name, in 
Ceara. Notice the square, board-lined water hole dug in the dry river 
bed. 
roughly the first six months of the year, 1s wet; summer, the 
second semester, 1s dry. Thus, for example, data from the ten 
meteorological stations maintained in Ceara state by the Servi¢go de 
Meteorologia indicate that g1 % of the aggregate annual precipita- 
tion normally falls in the winter months. The 3,000 kilometer 
(2,000 mile) long Sao Francisco River, rising in the humid moun- 
tains of Minas Gerais, flows through the southern section of the 
region under consideration. All other streams, fed directly by 
surface runoff, are subject to violent floods and, in the dry season, 
are sectioned into isolated pools. The Jaguaribe River basin, in 
Ceara, is typical. Although it drains an area one and a half times 
that of the Rio Grande upstream of Elephant Butte, it is an 
intermittent stream, often facetiously referred to as the largest dry 
river in the world (Figure 2). At intervals, the rainy season sets in 
late and/or shows a marked downward deviation from normal. 
When acute moisture deficiencies occur two or more years 1n suc- 
cession, all economic activities are disrupted—the séca (drought) 
has struck once more. 
The fact that the island-like eminences rising above the level 
of the old basement—be they crystalline ranges or sedimentary 
tablelands—as well as the dissected eastern slopes of the Borbo- 
rema, and the Ibiapaba escarpment to the west, are all favored by 
