INCREASE IN THE WATER SUPPLY.
Irrigation has been practiced in different portions of the Arid Region for the last twenty-five or thirty years, and the area cultivated by this means has been steadily increasing during that time. In California and New Mexico irrigation has been practiced to a limited extent for a much longer time at the several Catholic missions under the old Spanish regime. In the history of the settlement of the several districts an important fact has been uniformly observed—in the first years of settlement the streams have steadily increased in volume. This fact has been observed alike in California, Utah, Colorado, and wherever irrigation has been practiced. As the chief development of this industry has been within the last fifteen years, it has been a fact especially observed during that time. An increase in the water supply, so universal of late years, has led to many conjectures and hypotheses as to its origin. It has generally been supposed to result from increased rainfall, and this increased rainfall now from this, now from that, condition of affairs. Many have attributed the change to the laying of railroad tracks and construction of telegraph lines; others to the cultivation of the soil, and not a few to the interposition of Divine Providence in behalf of the Latter Day Saints.
If each physical cause was indeed a vera causa, their inability to produce the results is quite manifest. A single railroad line has been built across the Arid Region from east to west, and a short north and south line has been constructed in Colorado, another in Utah, and several in California. But an exceedingly small portion of the country where increase of water supply has been noticed has been reached by the railroads, and but a small fraction of one per cent. of the lands of the Arid Region have been redeemed by irrigation. This fully demonstrates their inadequacy. In what manner rainfall could be affected through the cultivation of the land, building of railroads, telegraph lines, etc., has not been shown. Of course such hypotheses obtain credence because of a lack of information relating to the laws which govern aqueous precipitation. The motions of the earth on its axis and about the sun; the unequal heating of the atmosphere, which decreases steadily from equator to poles; the great ocean currents and air currents; the distribution of land and water over the earth; the mountain systems—these are all grand conditions affecting the distribution of rainfall. Many minor conditions also prevail in topographic reliefs, and surfaces favorable to the absorption or reflection of the sun’s heat, etc., etc., affecting in a slight degree the general results. But the operations of man on the surface of the earth are so trivial that the conditions which they produce are of minute effect, and in presence of the grand effects of nature escape discernment. Thus the alleged causes for the increase of rainfall fail. The rain gauge records of the country have been made but for a brief period, and the stations have been widely scattered, so that no very definite conclusions can be drawn from them, but so far as they are of value they fail to show any increase. But if it be true that increase of the water supply is due to increase in precipitation, as many have supposed, the fact is not cheering to the agriculturist of the Arid Region. The permanent changes of nature are secular; any great sudden change is ephemeral, and usually such changes go in cycles, and the opposite or compensating conditions may reasonably be anticipated.
For the reasons so briefly stated, the question of the origin and permanence of the increase of the water supply is one of prime importance to the people of the country. If it is due to a temporary increase of rainfall, or any briefly cyclic cause, we shall have to expect a speedy return to extreme aridity, in which case a large portion of the agricultural industries of the country now growing up would be destroyed.
The increase is abundantly proved; it is a matter of universal experience. The observations of the writer thereon have been widely extended. Having examined as far as possible all the facts seeming to bear on the subject, the theory of the increase of rainfall was rejected, and another explanation more flattering to the future of agriculture accepted.
The amount of water flowing in the streams is but a very small part of that which falls from the heavens. The greater part of the rainfall evaporates from the surfaces which immediately receive it. The exceedingly dry atmosphere quickly reabsorbs the moisture occasionally thrown down by a conjunction of favoring conditions. Any changes in the surfaces which receive the precipitation favorable to the rapid gathering of the rain into rills and brooks and creeks, while taking to the streams but a small amount of that precipitated, will greatly increase the volume of the streams themselves, because the water in the streams bears so small a proportion to the amount discharged from the clouds. The artificial changes wrought by man on the surface of the earth appear to be adequate to the production of the observed effects. The destruction of forests, which has been immense in this country for the past fifteen years; the cropping of the grasses, and the treading of the soil by cattle; the destruction of the beaver dams, causing a drainage of the ponds; the clearing of drift wood from stream channels; the draining of upland meadows, and many other slight modifications, all conspire to increase the accumulation of water in the streams, and all this is added to the supply of water to be used in irrigation.
Students of geology and physical geography have long been aware of these facts. It is well known that, under the modifying influences of man, the streams of any region redeemed from the wilderness are changed in many important characteristics. In flood times their volumes are excessively increased and their powers of destruction multiplied. In seasons of drought, some streams that were perennial before man modified the surface of the country become entirely dry; the smaller navigable streams have their periods of navigation shortened, and the great rivers run so low at times that navigation becomes more and more difficult during dry seasons; in multiplied ways these effects are demonstrated. While in the main the artificial changes wrought by man on the surface are productive of bad results in humid regions, the changes are chiefly advantageous to man in arid regions where agriculture is dependent upon irrigation, for here the result is to increase the supply of water. Mr. Gilbert, while engaged during the past season in studying the lands of Utah, paid especial attention to this subject, and in his chapter has more thoroughly discussed the diverse special methods by which increase in the flow of the streams is caused by the changes wrought by man upon the surface of the earth. His statement of facts is clear, and his conclusions are deemed valid.