Bulletin 1.pdf - California Department of Water Resources - State of ...

WATER RESOURCES OF CALIFORNIA 191
The four precipitation stations listed in Table 46 were selected as
representative of elevations and topographic patterns within the Area.
Maximum and minimum precipitation figures in the table are monthly
extremes during the period of record. The bar diagrams of Plate 17,
"Distribution of Precipitation at Selected Stations, South Coastal Area,"
show graphically for these stations the monthly distribution of precipitation
in the maximum and minimum seasons of record. Also shown is
monthly distribution during the season in which precipitation was nearest
to the average seasonal total given in Table 46.
Mean seasonal precipitation on valley and mesa lands of the South
Coastal Area for the period from 1897-98 to 1946-47 is estimated to have
been 2,470,000 acre-feet, as shown in Table 47. Valley lands of this Area
lie chiefly in three regional groups, each of which receives light to moderate
rainfall. In the northern end of the Area, in Ventura County, valley
floor precipitation averages about 15 inches per season. The largest
regional group of valley lands in the Area is in the basins of the Los
Angeles, San Gabriel, and Santa Ana Rivers, where average precipitation
ranges from about 12 inches seasonally along the coast to about 20 inches
near the base of the mountains. Precipitation on valley and mesa lands
of this regional group is listed in Table 47 by ground water basins, rather
than by surface drainage basins as elsewhere. In San Diego County, in
the southern end of the Area, valley lands are scattered along the coast
and in pockets along streams draining the interior. Average seasonal
valley floor precipitation in this county ranges from about 10 to about 20
inches, increasing with distance from the ocean.