212 THE FUTURE OF ARID LANDS 
reservoirs should be promoted almost in terms of a logical response 
to conditions of the physical earth. 
Promoting Better Use of the Land 
The geographer, furthermore, concerns himself with the region 
as a whole. He is thus susceptible to the fact that the impounding 
of water for irrigation purposes, when unaccompanied by other 
measures (as, by and large, has been the case in the Nordeste), at 
best benefits only the irrigable lands downstream from the reser- 
voir. With the exception of a narrow tract immediately contiguous 
to the water line, it is indifferent to the fate of the soils in the 
watershed, yet some of these may be counted among the more 
promising for agriculture and support a considerable portion of 
the rural porno. 
The crystalline serras, which rise above the gently undulating 
sertao are a case in point. They receive the benefit of abundant 
and, what is particularly important, more dependable precipita- 
tion. Although the location of meteorological stations, as a rule, 
is not such as to favor the portrayal of local climatic contrasts 
resulting from the topography, it is obvious that sharp transitions 
occur within a very few miles. Observe, for instance, that rainfall 
at Meruoca, an upland locality (elevation about 670 meters or 
2,200 feet), is more than double that of Sobral, a lowland town 
(elevation about 70 meters or 230 feet), only 23 kilometers (14 
miles) away: 1,732.3 millimeters (67.56 inches) and 852.4 milli- 
meters (33.24 inches), respectively. The higher parts of the relief 
seem to derive additional benefit from the fact that they rise into 
and are probably dampened by the cloud cover which sweeps 
tantalizingly across the low country. The mantle of weathered 
rock and soil is thicker, as much as 25 meters (82 feet) depth 
having been reported for the Serra da Baixa Verde (13), and the 
relics of former forests, still to be found in some of the serras 
(Figure 8) may be contrasted with the dry caatinga of the sur- 
rounding plains (Figure 9). 
Although handicapped by less advantageous topography, the 
serras, with their smaller holdings, are devoted largely to farming 
—corn, beans, sugar cane, fruits and coffee being typical products. 
Saegeed of their former vegetation and improperly cultivated 
