Southern California has become an icon for the modern urban society, enabled by our ability to manipulate nature's hydraulics. This growing semi-arid region of 17 million people has met its water needs by diversifying its supplies and importing water from afar since the 1920's. The Metropolitan Water District of Southern California was formed in 1928 to develop, store and distribute water to its residents. The challenge of supplementing local water supplies continue and become more complex with increased competition for water, continued population growth, increased environmental and water quality needs and now, concerns over increased supply variability due to climate change.

Metropolitan imports about two-thirds of the region's water supply via large aqueduct systems from the Colorado River and from the Sacramento/San Joaquin River Delta. Metropolitan's role as a supplemental water supplier has evolved to one planning and coordinating for regional supply reliability for urban Southern California. Metropolitan works in concert with its 27 member agencies to which it delivers imported water.

Metropolitan uses a variety of meteorological and climate data in its operational and planning functions, respectively. Meteorological data is used to help predict seasonal and even daily water demands to help manage flows within its storage, treatment and distribution system. Climate data is used as a parameter within long-term water demand models.

Metropolitan has developed an integrated water resources plan to meet the growing needs of urban Southern California. Metropolitan's resources portfolio has diversified and expanded to include investments in groundwater storage, wastewater recycling, water conservation and demand management, and desalination. Through arrangements with other water providers, Metropolitan is able to store water available in wet years in groundwater basins statewide and exchange it for other water in dryer years, increasing the available supply. Wastewater recycling investments create a reliable, locally-controlled water resource providing over five percent of the region's supplies which is expected to grow to nearly ten percent by 2020. Metropolitan invests in groundwater desalination and has formed a public/private partnership to advance the development of cost-effective seawater desalination technology. At the core of Metropolitan's resource strategy are cost-effective water conservation and demand reduction technologies. Investment of over $220 million in this tactic has allowed Metropolitan to reduce its imported water demands by about 65,000 acre feet per year.

Managing the effects of a global warming will take better planning tools allowing for more detailed and confident forecasts of a warming's effect on hydrology. It may also require revision of operating parameters for water supply infrastructure, new infrastructure investment and additional investments in conservation and demand management to manage increase variability of supplies and higher demands due to warmer temperatures.