160 THE FUTURE OF ARID LANDS 
evaporation or transpiration between the points of origin and 
downstream use. 
Disregarding the relatively small additional amount of water 
that we might, with diligent effort, cause to flow out of our 
natural watersheds, we still have millions of acre-feet remaining 
there. It may be well to ask: What forage is this water now pro- 
ducing, compared with its potential productivity? Also, what 
needed commodities are produced by the water now being lost in 
transit between the point of origin and the point of downstream 
use? 
If we accept the premise that evaporation and transpiration 
potentials are such that normally any precipitation not leaving a 
watershed will ultimately be consumed by whatever type of 
vegetation that may be present or by evaporation alone, then is it 
unreasonable to assume that we could, through replacement of 
undesirable plants with desirable plants, develop a forage produc- 
tion that we do not have today? 
If we are correct also in assuming that large quantities of water 
are consumed by non-beneficial vegetation in stream channels, is 
there not reason to believe that we can eftect large savings of 
water by the removal of such vegetation? 
In summary, is there not every reason to believe that the part 
of the 220,600,000 acre-feet of water which is not now reaching 
points of downstream use and which 1s not now being put to bene- 
ficial use on natural watersheds, represents the real potential for 
increased production of needed commodities in our particular 
arid area? 
If the answer to these questions 1s yes, it appears that we should 
direct our attention, action, and our research toward ways and 
means of changing the use of water on our natural watersheds 
from non-beneficial to beneficial use. 
Although this discussion has been directed toward a particular 
segment of a particular country, reasoning applied here probably 
is applicable to other arid areas. 
REFERENCE 
1. Thornthwaite, C. W., with H. G. Wilm and others. 1945. Report of 
the Committee on Evaporation and Transpiration, 1943-44. dm. 
Geophys. Union Trans. of 1944, pp. 686-93. 
