Case Study: Factors affecting California’s water supply

Question 1

Geographical Controls on water supply:

Answer 1

 Mountain chains run parallel to the coast and prevent moist air reaching inland
 Most rainfall falls in a coastal zone no more than 250km wide
 South and far east of California receive under 100mm of rainfall due to the rain shadow cast by the Sierra Nevada mountains
 High pressure systems over the Pacific ocean block moist air currents reaching southern California
 Most of the major rivers are fed by snowmelt from the Sierra Nevada Mountains.
 In recent years extended droughts have meant groundwater and surface storage levels have
decreased

Question 2

Threats: Precipitation

Answer 2

 Much of California is arid with annual average precipitation of between 200-500mm
 65% of precipitation is lost through Evapotranspiration, 13% flows out to sea = only 22% for human use
 50% of the rain falls between November and March = seasonal shortages

Question 3

Threats: Population

Answer 3

 Has grown from 2 million people in 1900 to 37.7 million in 2007
 Spatial imbalance as three quarters of demand for water comes from areas south of the
Sacramento – 75% of the rain falls to the north
 Increasing demands for water exceed natural supplies