Climate Change Impacts #2: Water Supplies

I want to talk about the second of the three big climate change impacts Carpinteria will face in the coming years: fresh water supplies. Water is a more complicated issue than the first impact I talked about (sea-level rise). There’s less agreement about what’s going to happen, more variables to consider. But the impact is likely to be serious.

We all need fresh water. We need it for personal use, for industry, and for agriculture. Without adequate water, most of Carpinteria’s essential economic activities would be impossible. Sea-level rise might cost us some coastal homes and beaches, but without fresh water Carpinteria as we know it will cease to exist.

The Big Picture

Carpinteria currently imports 50% to 70% of the water it uses. In thinking about future water supplies, therefore, it is important to look beyond the Carpinteria valley to the statewide water system. Most of California’s water arrives as rain or snow in the northern half of the state, but ends up being used in the southern half of the state. The large-scale infrastructure projects — pipelines, aqueducts, and pumping stations — that transfer that water from north to south have been essential in allowing the development of southern California. A few places in the south (including Carpinteria) have significant local water of their own, but the majority of southern California’s roughly 22 million inhabitants (60% of the state’s population) are completely dependent on imported water.

Even without climate change, California faces a water problem. Projections call for significant population growth in the years ahead, and as the population grows so will the need for water. There really are only two ways to deal with that: increase the overall supply by accessing or creating new sources, or reduce per-capita demand through conservation.

Unfortunately, climate change threatens to make both strategies harder to pull off. For starters, climate change will make things hotter. This figure, from the 2009 state report on climate adaptation, shows predicted maximum July temperatures over the coming decades. (You can click the image for a larger version.)

Imagine a California with summer heat waves that are hotter, longer, and more frequent. That’s the world our children and grandchildren will live in. With hotter conditions, demand for water goes up.

If you look carefully at the map, you can see that the most dramatic temperature increases will occur inland. Coastal communities like Carpinteria will be protected somewhat by the cooling effect of the ocean. But since Carpinteria competes with those inland communities for water, the increased heat will still affect our water situation.

That’s the demand side. Now let’s look at supply. There’s actually some good news here (at least potentially). Warmer air holds more moisture, so climate change can lead to more violent storms that deliver more precipitation. It’s possible that California will become wetter overall due to climate change. Unfortunately, climate change also tends to shift regional weather patterns, causing some places to become wetter while others become dryer, so it’s also possible that California will end up receiving less precipitation overall. No one really knows.

There will be other impacts, though, that will almost certainly have a negative effect. As I mentioned before, most of the fresh water used in the southern half of California comes from the north, in particular from the canals and pipelines that make up the State Water Project (SWP). Because of the sea level rise caused by climate change, there is likely to be significant saltwater intrusion into the Sacramento delta, reducing the effectiveness of the SWP, which in turn will reduce the amount of fresh water available to send south. We can address this with large-scale infrastructure projects like the proposed-but-never-completed Peripheral Canal, but the cost of such engineering is high.

A bigger problem is this: Currently, most of California’s precipitation arrives in the winter, while peak water demand happens in summer. We deal with this imbalance in two ways:

  • Man-made impoundments (lakes and reservoirs) hold winter runoff so it can be used later.
  • The Sierra snowpack serves as a huge natural reservoir, releasing its water in the form of snowmelt during the summer months.

Climate change throws a monkeywrench into this system. As discussed above, winter storms will likely become more severe, which increases the risk of flooding, which means water managers need to keep water levels in their reservoirs lower in order to have excess capacity to absorb storm flows. That in turn means they will tend to have less water available for use in the summer.

The biggest problem is this, though (again, you can click the image for a larger version):

Warmer temperatures mean that winter precipitation will tend to fall as rain, rather than snow. The result will be a dramatic decrease in the Sierra snowpack. How much of a decrease is unclear; as you can see from the above maps, the predications cover a wide range, from a 60% reduction in the typical April snowpack to an 80% reduction for the scenarios analyzed here. Even at the milder end of the predictions, though, that reduced snowpack is going to be a major problem for the state’s water supply.

So, as a result of climate change it seems likely that California will experience significant increases in water demand along with significant decreases in supply. Basic economics tells us what will happen then: Water is going to get very, very expensive.

What This Means for Carpinteria

So, that’s the big picture. What does this mean for us here in Carpinteria?

I expect we will experience increasing competition for scarce water supplies, with wealthier and more-powerful entities (like the major urban centers of southern California) using their muscle to get the water they need, while less-wealthy and less-powerful communities struggle. The “water wars” of the 20th century, in which the city of Los Angeles diverted water from the once-thriving agricultural communities of the Owens Valley, offer an example of what such competition might look like.

I think we in Carpinteria need to think carefully about this, and do our best to plan ahead. We’re actually better off than many other southern California communities, because as I mentioned above, we have our own local sources of water. The aquifer that underlies the Carpinteria valley currently supplies 30% to 50% of our water. We also receive significant winter rainfall. Assuming we can maintain local control of our water resources, we will be in a relatively good position.

Here are some ideas for things we could do to help us prepare:

  • Institute a groundwater management plan: Currently, Carpinteria’s groundwater is completely unregulated. Public and private well operators pump as much or as little water from the aquifer as they like. As the cost of water rises, it will be important that we have a legal framework in place to prevent over-pumping, which would lead quickly to exhaustion of the shared resource.
  • Promote increased groundwater recharge: Most of the rain that falls on Carpinteria flows quickly out to sea, a process that was made more efficient during the last century by creek channelization projects that prioritized flood control over groundwater recharge. As part of a groundwater management plan, we could work to balance flood control with the need to maintain our aquifer. We could examine things like dechannelization and the creation of impoundments to allow more of our local rainfall to soak into the ground. Zoning provisions that promote permeability and reduce runoff could be strengthened.
  • Institute a significant, sustained water conservation effort: We’re going to have to make do with less water in the years ahead. The sooner we get serious about conservation, the more we will be able to accomplish. We could explore reclamation, and the creation of a parallel system for delivering reclaimed water for landscaping and agriculture. We could use more rain barrels to collect runoff from our roofs. We could promote the replacement of residential lawns with less-thirsty alternatives. And so on.
  • Construct a front-country reservoir: By constructing a reservoir in the hills above Carpinteria, we may be able to capture enough rain to make up for the water we currently import. This would be a big step, but if we plan carefully and get started soon enough, it might represent our best chance of achieving the kind of local self-sufficiency that would allow us to survive a major state water crisis.

I’m no expert; I’m just some guy who’s interested in the subject and has done some reading. Some of the things I’ve said here may be wrong, and there may be other approaches I haven’t mentioned that would work better. As I’ve already mentioned, even for the experts this is a murky subject with lots of uncertainty, and the farther into the future we try to look the more uncertain things become.

But this much is clear: Of all the challenges Carpinteria faces as a result of climate change, maintaining adequate supplies of fresh water is likely to be one of the most important. No other problem I can foresee poses as clear a threat to Carpinteria’s existence. We need to take this problem seriously.

See climate change adaptation resources for more information.