Report on the lands of the arid region of the United States, with a more detailed account of the lands of Utah

by John Wesley Powell; Willis Drummond; Clarence E. Dutton; Grove Karl Gilbert; A. H. Thompson

On the whole, it appears that the white man causes a greater percentage of the precipitation in snow to be melted and a less percentage to be evaporated directly. This follows from the destruction of trees and of grass. By reducing the amount of vegetation he gives a freer flow to the water from rain and melting snow and carries a greater percentage of it to streams, while a smaller percentage reaches the air by evaporation from the soil. By the treading of his cattle he diminishes the leakage of the smaller water channels, and conserves the streams gathered there. By the same means and by the digging of drains he dries the marshes and thereby enlarges the streams. In all these ways he increases the outflow of the land and the inflow of the lake. He diminishes the inflow in a notable degree only by irrigation.

The direct influence of irrigation upon the inflow is susceptible of quantitative statement. Four hundred square miles of land in Utah and Idaho are fertilized by water that would otherwise flow to the lake, and they dissipate annually a layer of about 20 inches. To supply these 20 inches the drainage district of 16,000 miles yields an average layer of 0.5 inch, and this yield is in addition to the 1.4 inches required to maintain the increase of lake surface. The total augmentation of the annual water supply is therefore represented by a sheet 1.9 inches in depth covering the entire district.

The indirect influence of irrigation, and the influences exerted by the grazier and the woodman, cannot be estimated from any existing data, but of their tendencies there can be no question. To some extent they diminish local evaporation, and induce a larger share of the rainfall to gather in the streams; and to one who has contrasted the district in question with similar districts in their virgin condition, there seems no extravagance in ascribing to them the whole of the observed change.

In the valley of the Mississippi and on the Atlantic coast, it has been observed that the floods of rivers are higher than formerly, and that the low stages are lower, and the change has been ascribed by Ellet and others to the destruction of the native vegetation. The removal of forests and of prairie grasses is believed to facilitate the rapid discharge from the land of the water from rain and melted snow, and to diminish the amount stored in the soil to maintain springs. In an arid country like Utah, where the thirst of the air is not satisfied by the entire rainfall, any influence that will increase the rapidity of the discharge must also increase the amount of the discharge. The moisture that lingers on the surface is lost.

On the whole, it may be most wise to hold the question an open one whether the water supply of the lake has been increased by a climatic change or by human agency. So far as we now know, neither theory is inconsistent with the facts, and it is possible that the truth includes both. The former appeals to a cause that may perhaps be adequate, but is not independently known to exist. The latter appeals to causes known to exist but quantitatively undetermined.

It is gratifying to turn to the economic bearings of the question, for the theories best sustained by facts are those most flattering to the agricultural future of the Arid Region. If the filling of the streams and the rise of the lake were due to a transient extreme of climate, that extreme would be followed by a return to a mean condition, or perhaps by an oscillation in the opposite direction, and a large share of the fields now productive would be stricken by drought and returned to the desert.

If the increase of water supply is due to a progressive change of climate forming part of a long cycle, it is practically permanent, and future changes are more likely to be in the same advantageous direction than in the opposite. The lands now reclaimed are assured for years to come, and there is every encouragement for the work of utilizing the existing streams to the utmost.

And finally, if the increase of water supply is due to the changes wrought by the industries of the white man, the prospect is even better. Not only is every gain of the present assured for the future, but future gain may be predicted. Not alone are the agricultural facilities of this district improving, but the facilities in the whole Rocky Mountain Region are improving and will improve. Not only does the settler incidentally and unconsciously enhance his natural privilege, but it is possible, by the aid of a careful study of the subject, to devise such systematic methods as shall render his work still more effectual.

FARMING WITHOUT IRRIGATION.

The general rule that agriculture in Utah is dependent on artificial irrigation finds exception in two ways. First, there are some localities naturally irrigated; and, second, there is at least one locality of which the local climate permits dry farming.