METEOROLOGICAL DISCUSSION 



The ratio of rainfall to evaporation cannot be exactly determined as 

 data for evaporation are meager or wholly lacking. It has been deemed 

 worth while nevertheless to get an approximate notion of this ratio by 

 estimating the evaporation and dividing by the normal rainfall. In 

 the following table this has been done and the results appear in the 

 last column headed Ratio. This table also shows the maximum and 

 minimum annual precipitation at each station during the observation 

 period shown in column 2. 



El Paso 



San Luis Potosi 



Chihuahua 



Fort Wingate... 



Fort Yuma 



Phoenix 



Tucson 



Mohave 



Hawthorne 



Winnemucca.... 



St. George 



Fort Duchesne. 



Prineville 



Lost River 



Laramie 



Torres 



*From 15 years observations. tFrom 22 years observations. 

 Discussion. — The foregoing meteorological data are given concern- 

 ing localities which very clearly lie within the true desert regions of 

 North America. It would be impossible to outline the included areas 

 upon a map except by means of data obtained by an accurate and ex- 

 tended hydrographic and biological survey. The rate of evaporation 

 for the several localities mentioned is roughly estimated from data 

 taken from the Report on the Climate of Arizona by Greely and Glass- 

 ford in 1891. It is probable that actual measurements might show 

 a variation of ten per cent by way of error in these estimates, but the 

 amount given may be regarded as fairly approximate for the regions in 

 which the several stations are located. It is to be seen that the evapo- 

 ration at Tucson, Arizona, and at Laramie, Wyoming, is about seven 

 times as great as the normal precipitation, while the evaporation at 

 Yuma, Arizona, is more than thirty-five times as great as the average or 

 normal amount of precipitation. The evaporation at the last named 

 locality amounted to one hundred and sixty times as much as the pre- 

 cipitation in the year 1899. 



