32 
PACIFIC SCIENCE, Vol. XII, January, 1958 
MONTH 
Fig. 8. Computed evaporation (E c ) and pan evaporation (E p ). 
The difference, evaporation minus precipi- 
tation, has a maximum in early summer, a 
minimum during the rainy season, and a 
secondary maximum immediately after the 
rainy season. Except for Mazatlan during the 
peak of the rainy season, evaporation exceeds 
precipitation during all months of the year. 
The few available data indicate that the mean 
annual evaporation for the southern half of the 
Gulf lies between 1500 and 3000 mm. For the 
entire Gulf, considering the dry northern part, 
roughly 2500 mm. can be taken as a con- 
servative estimate for the mean yearly evapo- 
ration. With this value the rate of evaporation 
over the entire surface of the Gulf becomes 
5.25 x 10 n m 3 /year or 1.7 x 10 4 m 3 /sec. 
GENERAL CIRCULATION 
The bulk of water in and near the Gulf of 
California is the same as in the equatorial 
Pacific, slightly modified at the surface by 
extensive evaporation and by the admixture 
with water brought south by the California 
Current. The influence of the latter is re- 
stricted to the vicinity of Cabo San Lucas. 
The great similarity between the Gulf and 
Pacific Equatorial water, below the thermo - 
cline, is illustrated by the close agreement 
