30 THE FUTURE OF ARID LANDS 
Drought prediction for a few years ahead has great immediate 
interest. Although one can arrange the data from previous years 
by cycles, up to now none of these can be projected into the 
future as a sound basis for prediction. Yet the problem is so im- 
portant that active research is continuing, and the chances for 
such long-time predictions steadily improve with studies of the 
mass movements of the upper air and the factors which influence 
them. 
Recently some people have tried ‘‘to do something” about 
climate, or rather about the weather. We have no firm basis for 
guessing how important cloud seeding may turn out to be, nor 
will we until the scientists in this field have spoken more clearly 
than they have so far. 
Geomorphology 
The land forms of arid regions and the processes by which they 
are modified differ importantly from those of well-watered regions. 
Only in recent years have there been the detailed studies neces- 
sary to forecast the evolution of land forms well enough to plan 
enduring engineering measures and land-use schemes with reason- 
able certainty. In fact, world history is crowded with examples of 
such failures to predict landscape changes that ruined the works 
of man. Some of these failures were inevitable. Irrigation works 
and cities were located in places where it was inevitable that they 
would be destroyed by the natural processes of landscape change. 
Other failures were stimulated by overuse of the soil or by failures 
to build or to maintain simple protective works that would have 
been practicable for controlling the movement of water and of 
soil by wind or water. 
The geomorphologist has the task of sorting out the relatively 
stable from the relatively unstable landscapes and of predicting 
the changes that will be induced by changes in water courses and 
in the use of the land. 
Because of the low rainfall, arid soils generally have a sparse 
plant cover; thus normally the soil is exposed directly to wind and 
to running water. The fine particles of dry soil exposed to severe 
wind blow away, often to great distances. The sand moves more 
