188 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



MOUNTAIN SNOWFALL AVORK. 



For many j^ears liydraulic engineers engaged in the mountainous 

 regions of the West Avere confronted with discrepancies between 

 precipitation and run-off that were unexplainable at the time. In 

 many localities the total annual run-off would be greater than the 

 total measured precipitation. Tt was evident, of course, that the 

 measurement of the precipitation was deficient in some way, and it 

 was finally agreed that the trouble was due to the want of snowfall 

 measurements in the high mountains. 



Consequently, about three years ago a mountain-snowfall cam- 

 paign was inaugurated by the AVeather Bureau. Special apparatus 

 was devised, and about 275 mountain-snowfall stations were opened. 

 Snowfall measurements were made daily or weekly, according to the 

 locality, and the depth and water equivalent of the snow carefully 

 computed. Later it was found that some portions of the equipment 

 were not entirely suited to the conditions, and improved apparatus 

 has been devised in the form of a shielded rain and snow gauge. As 

 a result of the observations thus secured the difficulties of the 

 hydraulic engineer have already been lessened. The data are now 

 comparable, and computations of future water supply from the 

 winter snows in the mountains can be made with a considerable 

 degree of accuracy. 



Provision has also been made for measuring the water equivalent 

 of snow that must be depended upon to supply water for irrigation 

 purposes in a portion of the subarid West. A special snow survey 

 in Utah has demonstrated the possibility of making a reasonably 

 accurate forecast of the amount of water that will be available each 

 season for the uses of the irrigation farmer. If the supply promises 

 to be greater than usual, water-supply companies can arrange to 

 dispose of more water and farmers can cultivate more land. On the 

 other hand, if the supply promises to be less than usual, the water 

 distribution can be lessened and the area under cultivation be re- 

 stricted. The great utility of such advance knowledge is readily 

 apparent. 



BAROMETKY, THERMOMETRY, AND CLOUD OBSERVATIONS. 



In Volume II of the Annual Eeport of the Chief of the Weather 

 Bureau, 1900-1901, is published the "Barometry of the United 

 States and Canada." All the barometer data were reduced to a homo- 

 geneous system of station normals computed for the epoch January 

 1, 1900, requiring in the case of many stations a computation of the 

 record for 27 years. From these computations barometer tables for 

 the reduction of the pressure readings to sea level were computed. 



