used in the measurements are described generally, and the data col- 

 lected through i960 are summarized. Since the initiation of this 

 program in 195^^ improvements and standardizations within the pro- 

 gram have vastly Improved the quality of the data collected, such 

 that one hesitates to compare data collected In 196O with earlier 

 years of records. Consequently, Judgment was exercised in sum- 

 marizing certain of the earlier data. 



In Chapter IV, measured evapotranspiration rates described 

 in Chapter III are correlated with pan and atmometer evaporation 

 data which were collected concurrently at the evapotranspiration 

 plots. The pan and atmometer coefficients, so derived, are then 

 applied to the agroclimatic data to estimate evapotranspiration 

 for a few crops throughout much of the northern part of the State. 

 While comparisons are made with the values published In Bulletin 

 No, 2, it is not the Intent of this report to imply a question as 

 to the accuracy of previous values used by the department. In- 

 stead, this report Is Intended to Indicate some of the problems 

 involved In the collection and analysis of the data and, to the 

 extent of the data collected, to show tentative values that may 

 be used for the determination of water requirements for certain 

 crops. 



A great deal of the basic research fundamental to this 

 study was conducted by the University of California at Davis, both 

 prior to and since the initiation of this program. The continuing 

 counsel and guidance provided by various members of the University 

 of California have been of Invaluable assistance In the develop- 

 ment of these studies. 



