"Global Warming and Water Supply"

By Carol W. Kwan

Most scientists now agree that global warming is truly occurring. The only real debate concerns how fast it will occur. We need to be taking steps to deal with its ramifications, especially for water.

Global warming will impact our water supply. It will cause more extremes in the water cycle. Floods will get worse. Droughts will get worse. Both are bad for water supply.

More flooding means that water supply reservoirs must lower their water levels. This enables better protection of downstream communities from floods by providing more room to capture excess floodwaters.

Unfortunately, keeping reservoir water levels lower also reduces the amount of water that can be captured for water supply. If flooding becomes worse due to global warming, water managers will have no choice but to lower reservoir water levels to protect human life and property. The net result will be reduced water supplies.

More droughts mean that reservoirs will have longer, more severe dry spells to contend with. This reduces the total amount of water reservoirs can capture. Two thirds of the water used in Southern California originates in reservoirs on the Colorado River and in Northern California. More droughts will reduce the water from both of these sources.

The Southern United States and parts of the mid-west are currently experiencing a severe drought, especially in West Texas. Is this a portent of global warming's impact? It is hard to say. If global warming is already upon us, however, there are some specific things we can do to protect our water supply.

Three specific steps can help drought-proof our region: water conservation, water reuse, and ground water recharge.

Water conservation will help us prepare for global warming and help us protect environmentally-sensitive areas such as the Sacramento River Bay/Delta. Every gallon of water saved by using low volume toilets or low flow showerheads is a gallon that we do not need from Northern California. And this water can be saved regardless of how dry it is in the Colorado or Sacramento River watersheds.

Reuse of wastewater is another way to utilize a drought-proof source of water. Instead of letting wastewater flow to the ocean, it can be treated and reused for industrial water supply, parks, golf courses, and other non-potable uses. Direct potable reuse does not make sense, but there are plenty of non-potable ways we can use this water. Again, it will be available regardless of how dry it is in the parts of California where our water supplies originate.

Finally, more recharge of our groundwater basins can help us prepare for the potential impacts of global warming. One third of Southern California's water comes from groundwater, which is recharged primarily by rainwater. Unfortunately, much of the Los Angeles area is now paved over. This forces the rainwater to flow into the ocean unused rather than percolated into our ground water basin.

We need to find more and better ways to manage our watersheds and recharge rainfall into our groundwater basins. This duplicates the natural recharge that occurred before we paved over much of our region. Once in our groundwater basins, this water can remain in reserve for many years until needed during a dry spell.

I know what it is like to turn on the tap and not get any water. I was born in a part of the world where the tap water was frequently unavailable and rarely safe to drink. I have been spoiled during the past 29 years I have lived in the South Bay: I have always counted on safe, plentiful water when I turn on the faucet. Global warming cannot be allowed to change that.

Carol Kwan

Ms Kwan is a former director on the Metropolitan Water District of Southern California board and is currently a director on the West Basin Municipal Water District, where she is the first woman and first Asian American to serve on that board.