72 



insolation as it is termed, suggests certain upper limits to the 

 amount of water that may be vaporized over large swamp areas. 

 Average daily records of insolation are published in the Monthly 

 Weather Review for stations at La Jolla, Pasadena and Fresno. 

 The equivalent water of vaporization for the insolation received 

 at Pasadena and Fresno for the calendar year 1929 is as follows: 



Equivalent water 

 of vaporization 

 Total annual-, / at 68 degrees 

 Station insolation —' Fahrenheit 



Gram calories per Depth 



square centimeter in feet 



Pasadena l65,4l6 9.27 



Fresno 169,691 9-51 



Average -- 9-39 



"This suggests that, if all of the radiant energy received 

 from the sun were used in vaporizing water, it would be possible 

 to lose 9-39 acre-feet per acre annually, as an average for the 

 two stations, as the result of insolation. 



"Using the Fresno records for the period April 28 to May 

 27, 1929, we have the insolation as 20,467 gram calories per 

 square centimeter and the equivalent water of vaporization at 

 68 degrees Fahrenheit as 13. 8 inches. This is for the same per- 

 iod that the indicated loss from the swamp on Temescal Creek was 

 12.9 inches. It is likely, then, that the rate of loss was ap- 

 proaching its probable maximum when the tests on Temescal Creek 

 ceased, due to a failing water supply late in May. There is some 

 additional supply of heat to the swamp area from the s\irrounding 

 rocky canyon walls and from the strong draft of air flowing 

 through the canyon. On the other hand, not all of the insolation 

 received directly on the swamp area is used in vaporization. 

 Some of the radiant energy is stored in combination within the 

 plant tissues, some is reflected from the plant surfaces and part 

 goes into heat storage and in part is again radiated back to the 

 sky. 

 17 Direct plus diffuse received on a horizontal surface. 



