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California's water issues - where has the water gone?

Updated on March 6, 2017

Threats to the Californian dream


  • Much of California is arid, with an average annual precipitation of between 200-500 mm.
  • 65% of that precipitation is lost through evaporation and transpiration, while 13% flows out to sea - leaving only 22% as runoff for human use.
  • 50% of California's rain falls between November and March leading to seasonal shortages.


  • California's population has grown from only 2 million people in 1900 to 10 million in 1950, and 37.7 million by 2007. It is likely to reach 45-50 million by 2025.
  • It is not just the overall size and rate of growth of California's population that is creating a water problem, but also its spatial imbalance. 3/4 of the demand for water comes from the heavily populated areas to the South of Sacramento, while 75% of the precipitation falls in the North.
  • The increasing demand for water exceeds California's natural supplies.

Californian crisis

California's drought of 2000-2007 has forced Californians to wake up to the problem of water supply. California's status as the USA's leading economy, a major supplier of food (and home to three of the worlds largest cities), is now at risk. Building and maintaining the Californian dream has been at the expense of the natural environment.

  • Wetlands have been drained, natural habitats altered, and fish stocks depleted, to secure water supplies.
  • Additional problems are polluted waterways, the over-extraction of groundwater and increasing salinity.
  • The Bay-Delta region and the Salton sea have become environmental disaster zones, and the once mighty Colorado River has been reduced to little more than a trickle as it enters the Gulf of California.

State Water Project
Central Valley Project
Colorado River
It contains 20 major dams and reservoirs
It contains 22 dams and reservoirs
It contains 11 major dams/reservoirs
It irrigates 0.3 million hectares of farmland
It irrigates 1.2 million hectares of farmland
It irrigates 1.4 million hectares of farmland
It provides drinking water for nearly 20 million Californians
It provides drinking water for 2 million Californians
It provides drinking water for 25 million Californians

The Colorado River Basin under pressure

The huge Colorado River Basin drains 7% of the USA and covers an area 1.1 times the size of France. Throughout the 20th century, numerous treaties and agreements were needed to allocate 'fair shares' of its water to the seven surrounding US states, plus Mexico.

The flow of the river varies - it has a bi seasonal regime, with winter and summer peaks (tropical systems occasionally cause large floods in the Lower Basin).

North vs South

Because of the spatial imbalance between the distribution of the rainfall and the distribution of population in California (with too many people living too far away from the natural water sources) the State water project (SWP) was constructed in the late 1950's to provide water for Southern California. However, it has been controversial:

  • Northern Californians feared that their water would be 'owned' by the south.
  • Southern Californians demanded guarantees that water flows would be maintained.
  • The Bay-Delta region is where supplies are transferred, and it has become a sensitive area where multiple users all demand more water.

Sharing the Colorado

In 1901, the Alamo Canal was begun, to bring irrigation water from the Colorado River to the farmers of the Imperial Valley in southern California. However, political tensions with Mexico (through which much of the canal passed), meant that this water supply was not guaranteed. Therefore, the All-American canal was built to provide a secure water supply for California's growing agricultural economy. Mexico and the six other US states of the Colorado River Basin began to be alarmed that California's expanding use of the Colorado's basin was beginning to threaten their own water supplies.

The resulting agreements about water shares were based on flow patterns from the early twentieth century, when rainfall was about 10% higher than it is today. Pressures on the Colorado River are now building:

  • Mexico takes 10% of the total flow. States in the Lower Basin take 50% and the Upper Basin falls short by 10%
  • California takes 20% more than the original agreement
  • Native Americans are owed 5%, but could claim more

Native American water rights

In 1908, the Supreme Court recognised Native American water rights across the USA, regardless of whether a tribe had used the water or not.

In 1963, the Native American Reservation were granted the use of enough water to irrigate any land where it was practicable to do so. Five Reservations, with a total population of about 10,000 were granted approximately 5% of the Colorado's River flow. As a result, Native American tribes have the best water rights along the Lower Colorado River.

Planning ahead

The Colorado Compact was based on 1922 flow levels, but things have changed a lot since then. Lakes Powell and Mead in the Colorado river Basin have not reached capacity since 1999. Rainfall has been declining since the 1980s and the climate is changing. Population levels in the area have also increased dramatically since 1922, especially in California.

In December 2007, a new agreement was reached. Instead of sharing the Colorado's flow, the states will aim to divide the shortages. The actual amount of water available will determine the deliveries to each state.

Potential water saving prospects

Domestic conservation: 30% savings by repairing leaks, metering supplies and efficient appliances. 50% savings by planting California-friendly, drought tolerant plants and using smart sprinkler systems.

Groundwater banks: Saving storm water for release during dry periods.

Re-using wastewater: Cleaned water from sewage treatment plants currently flows into the sea. It could be re used for landscape irrigation and industry, or to recharge aquifers for later domestic use.

Reducing agricultural water usage: Farms currently use 80% of California's clean water. a 10% reduction would double the amount of water available for urban areas.

Smart planning: New housing developments should only be built where supplies of local ground and surface water are adequate for their needs.

Some examples of drought tolerant plants in Southern California
Some examples of drought tolerant plants in Southern California


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