HKDSE Geography/M5/Farming Inputs in Southern California

Weather and Climate
Southern California has a Mediterranean climate characterised by hot and dry summers (Apr -> Oct) and warm, humid winters (Nov -> Mar).

Insolation and Temperature
Insolation and temperature are high in Southern California. Southern California receives an annual temperature of 12 to 32 degrees.

It is hot in summer and warm in winter. This is both because it is located in mid-latitudes with high solar radiation input, and because the lack of cloud cover allows insolation to reach the ground directly without much scattering in the atmosphere.

Rainfall
Southern California receives scanty and unstable rainfall. The annual rainfall is around 200 to 500 mm. It mainly falls in winter. Annual variation of rainfall is great.

Rainfall decreases from north to south, and from east to west：
 * The coastal areas receive much relief rain thanks to the Coast Ranges. However, on the leeward side, the Central Valley receives very little rainfall because it is in the rain shadow.
 * The southern tip of California has a subtropical desert climate. Offshore winds remove moisture from the area throughout the year. Thus rainfall is very scarce.

Relief
The relief of Southern California is hilly, with the Sierra Nevada and Coast Ranges. However, extensive lowland can be found in the Central and Imperial Valleys, where much of the farming is concentrated.

Soil
The evaporation rate is very high, so soil moisture is low. Salinisation occurs:
 * As the insolation and temperature are high, evaporation rate is high.
 * The underground water rises to the earth's surface through capillary action.
 * The underground water is evaporated, leaving a hardpan layer of salt crust on the earth's surface. Farming is thus hindered and the soil is thus alkaline.

As there is little vegetation cover in Southern California, the soil fertility is low.

Drainage
It is mainly drained by the San Joaquin River in the Central Valley and the Colorado River in the Imperial Valley.