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  • Catie Thow

What Climate Change Means for California’s Rainfall and What You Can Do to Help

This is a guest article written by 2nd year graduate student Allie Margulies. Allie works with the San Francisco Bay National Estuarine Research Reserve and the Smithsonian Environmental Research Center Marine Invasions Lab where she studies how native Olympia oysters are affected by extreme weather related to climate change.

Looking back on the past few years, it feels as though Californians have faced a climate-related crisis almost every year, whether it’s related to floods, fires, or drought. Within the past decade, many Californians have become increasingly aware of their water usage after experiencing one of the most extreme multi-year droughts on record from 2012 to 2016. Then, in 2017 we experienced a record-breaking flood year. Now, in 2021 we are officially in another historic drought across the West Coast, with 95.56% of California in severe drought, and nearly half the state in exceptional drought (Figure 1). Personally, I know I have made many permanent changes to my daily life in order to save water, such as making more informed food choices and taking shorter showers. Unfortunately, climate modelers suggest our problem is likely to get worse.

Source: USDA
Figure 1: Western US Drought Monitor

An Age of Extremes

While California naturally experiences a lot of variability in rain from year to year and month to month, climate change modelers (Swain et al. 2018) project that this variability is going to become even more extreme. Both drought and flood years are likely to become more frequent, and we may already be facing an increased likelihood of these extremes. This is because climate change is causing changes in temperature and atmospheric circulation that affect the amount of pressure and water vapor in the atmosphere, which alters rainfall patterns. This variability can affect our daily lives with road closures and flooding during high rainfall years, and by forcing us to ration our water during dry years, increasing tensions between agricultural and environmental uses. Both flood and drought years can cause millions or even billions of dollars of damage and economic loss.


Climate change models predict that unless we curb greenhouse gas emissions, we can expect to see extremely dry winters over 80% more often in Northern California and over 140% more often in Southern California starting in only about 30 years (Swain et al. 2018). However, climate change projections also show that we will see an even bigger increase in extremely wet winters. While this comes with its own set of problems, it at least improves the likelihood that our multi-year droughts will get cut short by a heavy rain year. This could help relieve tensions between environmental and agricultural groups and help give us a temporary sense of security.

Flooding and Rainfall Seasonality

I may have made flooding sound like a good thing above, but trust me, it’s not. Remember in 2017 when we got so much rain that the Oroville Dam’s primary spillway failed and necessitated the evacuation of nearly a quarter of a million people (Figure 2)? Winters with a comparable amount of total rainfall are expected to increase in frequency by 100 to 200% during this century alone.

Source: CNBC
Figure 2: Flooded Road in California

Despite little overall change in average rainfall, our already short rainy season is projected to become even shorter, with up to a 40% increase in January and February precipitation, and up to a 50% decrease in September and May (Swain et al. 2018). This means that during winters with high rainfall we will be getting even more rain in a shorter amount of time, increasing flood risk. By 2060 we are more likely than not to experience at least one flood beyond any level that our modern water infrastructure has ever experienced. This would likely cause substantial loss of life and nearly a trillion dollars in economic damages. The shortening of the rainy season also means we will have a longer fire season with less chance of being saved by early rains in the fall. While so many Californians have already experienced intentional power outages or had to evacuate their homes in the last few years because of fires or floods, it seems only logical to expect this to become an increasingly normal part of living in the Golden State.

What you can do

I know this information paints a bleak picture, but you might be surprised at how easy it is to reduce your impact. First, the most important thing you can do is to support policymakers and policies that are serious about climate goals and preparedness.

Figure 3: Average Californian Water Use

On a more personal level, it can be easy to feel helpless about climate change, and while it’s really important to reduce your greenhouse gas emissions directly (driving less, etc.), it’s also really important to make informed food decisions! Despite California’s naturally dry climate, US Geological Survey reports that we use more water than any other state, which is due in large part to our enormous agriculture industry that produces two-thirds of America’s fruits and nuts! On average, agriculture accounts for 80% of California’s water usage, not counting flows left for environmental uses (which make up about 40% of the total) (Figure 3). This means we can make a big impact by using our money to support more sustainable foods and sustainable farming practices that minimize water usage. For most people, our food makes up at least half our personal water footprint and is one of the best ways we can make an impact. To see how you’re doing, I recommend going to

Much of the farming community has been working to improve their efficiency, and we can continue to encourage sustainable agriculture by not financially supporting the most water- and greenhouse gas-intensive foods, such as beef. This doesn’t have to be a full commitment if you’re not ready. It’s easy to take baby steps and choose more sustainable food, even just once a week, and make sure not to waste food you’ve already purchased. Choosing chicken instead of beef for just one meal every week can save over 18,000 gallons of water per person in just one year, and much more if you made that meal vegetarian instead!

You can find out your total water footprint and see where you personally might be able to reduce your water usage at

Small changes can add up to make a big impact. I know it’s cheesy, but it’s true that if everyone makes a little change, it really can make a big difference.

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