866 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
Because of the comparatively’ light rainfall in winter and complete 
absence of rain in summer, irrigation is, with the exception of a few 
limited areas, a necessity for successful orcharding in California. 
The problem of fruit-bud formation in California is further com¬ 
plicated by the fact that here latitude means little or nothing in 
determining climate. Isotherms normally run east and west. In 
California, with the high Sierra Nevada mountains on the east, the 
Pacific Ocean on the west, and minor mountain ranges on the north, 
south, and west, these isotherms are deflected so that their general 
direction is north and south (fig. 1). 
In California there are three distinct climatic belts differing in 
degree rather than kind. These are coast, valley, and mountain, 
depending on distance from the ocean, location with reference to 
Fig. 1.—Outline map of California, showing average annual precipitation in inches for 20-year period 
1894-1924; isotherms for mean annual temperatures in 1914; also the points from which fruit buds were 
collected 
mountain chains, and altitude for their climatic differences. Fruit¬ 
growing sections are found in all of these belts. 
The fruit-growing districts of the Pacific coast are located in pro¬ 
tected places just oack of low mountains, and are designated as 
coastal valleys. As compared with the interior valleys, these coastal 
valleys are characterized by warmer winters,* cooler summers, more 
abundant winter rainfall, slightly more humidity in summer, and 
frequent fogs. 
The interior valleys have the following general climatic character¬ 
istics: Higher summer and lower winter temperatures than the 
coastal valleys, abundant winter rainfall in the north decreasing 
rapidly southward; very dry air, free from fogs in the summer and 
with almost constant sunshine; occasional strong, hot, desiccating 
winds from the north in summer, and cold north winds in winter. 
