206 THE FUTURE OF ARID LANDS 
ce 
It is immaterial to speculate whether these “characteristics” 
refer to the zones or landscapes where the droughts obtain or to 
the sécas themselves: neither one nor the other has been charac- 
terized with any degree of precision. This perhaps may be one 
reason why there has been relatively little opposition to subse- 
quent amendments, which have enlarged the “‘legal”’ (but obvi- 
ously arbitrary) drought area to the point, for instance, where 
the boundary has advanced some 700 kilometers (more than 400 
miles) in a southwesterly direction (Figure 5). 
The way in which a single element was considered in setting up 
this operational region may be contrasted with the attention 
commonly dispensed by geographers to the interrelation of all 
pertinent phenomena occurring in a certain area. Whereas the 
amount of precipitation is unquestionably a basic control, it is 
not clear why the 600-millimeter isohyet was invested with the 
significance of a critical limit. Furthermore, the knowledge that 
rainfall operates in the presence of other factors should caution 
against the facile acceptance of the simplified sequence of cause 
and effect which the adopted criterion implies. Not only must 
other climatic components be considered, but it is necessary to 
take into account additional influences, such as slope and water- 
holding capacity of soils. Field work appears thus as an indispen- 
sable ally (not to say part) of climatological studies. 
Even supposing agreement had been reached concerning the 
value of precipitation to be considered critical in defining the area, 
the wisdom of drawing boundaries on the strength of rainfall 
measured during one single, exceptional period, such as 1930-32, 
remains open to question. The more customary procedure, of 
course, would utilize mean or normal conditions, on the basis of 
records extending back through the greatest possible number of 
years. One might, however, challenge the advisability of obscuring 
the unusual experiences in long averages, since, especially in the 
Northeast, it is the unusual conditions which are the greatest cause 
for concern. How then can one attempt to sharpen the technical 
meaning of the expression ‘‘érea da séca,” current in non-technical 
usage? A simple and apparently satisfactory approach might be 
based on the frequency of the occurrence of drought-producing 
