274 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 13 



than 47 meters (150 feet) from March 22, 1940, to April 2, 1942, 

 was 7.8 miles per hour. Two storm periods were severe enough to 

 break off the atmometer cups at the station on the central ridge, so that 

 the average of 16.8 miles per hour must be well under the actual average 

 for that station, and is probably approximate to an average for the 

 island as a whole. 



Variations in the wind velocity between different locations produce 

 a greater variation in evaporation rate than does the sun. The difference 

 between the evaporation rate on the windy north peak and that of the 

 northern exposure of Cave Canyon (cf. map, p. 359) for the same period 

 of seven months was 16.06 cc. per day, as measured by standardized 

 Livingston spherical white-cup atmometers. During the same period 

 the greatest difference in the evaporation rates of white-cup and similar 

 black-cup atmometers^ was recorded at the central ridge station, where 

 it averaged 10.81 cc. per day. That is, the effect of wind on evaporation 

 was approximately 50 per cent greater than that of the sun. 



Where the full force of the wind sweeps across comparatively level 

 areas on the headlands, the soil, as has been said, is shallow and coarse, 

 while on protected terraces it is deep and fine-grained. Entirely different 

 plant communities occupy the two areas. Exotic plants rarely invade the 

 windiest areas, although Mesemhryanthemum grows in some windy 

 localities. Astragalus Traskiae, Malacothrix foliosa, Hemizonia Cle- 

 mentina, and Baeria hirsutula are dominants of the windiest areas. 



Under Russell's modification of the Koppen international climatic 

 system the island would probably be described as possessing a "foggy 

 desert" type of climate. This classification, however, does not fit the 

 conditions existing on Santa Barbara Island. In view^ of the records 

 available for this island and those adjacent, and the general physiog- 

 nomy of the vegetation, it would seem fitting to apply the climatic 

 designation presented in section III — that of the arid maritime climate. 



It was not possible to obtain accurate records of the precipitation 

 with the type of rain gauges available. Even with the use of oil in the 

 rain gauges of the type used, there was considerable evaporation. The 

 latter is indicated by the fact that very much larger readings were 

 obtained from stations sheltered from the sun than from stations ex- 

 posed to the full sun.^ Also, the rain guage would overflow during 



5Black-cup atmometers absorb much of the sun's radiation which is re- 

 flected from the white-cup atmometers, and thus afford a measure of the influence 

 of insolation upon evaporation. 



^For November, 1940, the most sheltered station B 2, on the northern ex- 

 posure of Cave Canyon, recorded 2.13 inches of precipitation while the station 

 B 1, on a sunny southern exposure only about 50 meters from station B 2, recorded 

 only 1.00 inch of precipitation. 



