surface. It is believed that the crop surface roughness may, 

 thi'ouch greater air niixln,":, be one of the influencing factors. 



Average monthly pan and atmometer coefficients for 

 cotton for the tv;o years of record are presented in Table 8. 

 For purposes of comparin;c v/ith Bulletin 2 estimates, an average 

 coefficient for tlie Tulare Lake Basin Valley Floor Hydrographic 

 Units was determined for the grov/in;- season used in Bulletin 2. 

 For the period from May through October, the active growing season, 

 the average pan coefficient is 0.68, and the atmometer coefficient 

 is 0.0098. The monthly coefficients for the period from June 

 through September are considered to be primarily the effect of 

 climatic evaporative demand and crop conditions, and are not sub- 

 ject to the influence of early-or late-season nonbeneflcial uses. 



Application of Coefficients and Evaporation 

 Data to Estimation of Evapotranspiration 



Using the average pan or atmometer evaporation observed 

 in each area, as shown in Tables 2 and 3 in Chapter II, and ap- 

 plying the appropriate pan or atmometer coefficients as described 

 jn Tables 6, 7j and 8, estimates of monthly consumptive use values 

 viere made for several crops. These monthly estimates are summarized 

 in Table 9, and are compared v;it.j values utilized in Bulletin 2, 

 "Water Utilization and Requirements in California," published by 

 the department in 195b • To make the comparison with Bulletin 2 

 values valid, the grov/ing seasons used in Bulletin 2 were used 

 in all calculations for Tables 6 through 9- In general, the esti- 

 mates based upon the pan and atmometer coefficients are approximately 

 equal to or ;;reater than the Bulletin 2 values. This is also true 

 where measured values of consumptive use are available. This, in 



