Climate Change Impacts on California Central Valley: The Warning Shot the US Is Ignoring

December 16, 2021 | 12:04 pm
Dry Kern River, CAPeter Szera (
José Pablo Ortiz Partida
Senior Bilingual Water and Climate Scientist

While different places in the United States experience different climate impacts (e.g., more extreme precipitation in eastern states, stronger hurricanes in the Gulf, and dryer and hotter conditions across southwestern states), the Central Valley is expected to experience quite a few: hotter temperatures, droughts, wildfires, and extreme precipitation events. Because of this, and because of the Valley’s history of environmental and socioeconomic inequities and injustices, we are devoting a blog series to the region.

This series explores how worsening climate impacts are changing the landscape, affecting people and ecosystems, impacting the state’s agricultural economy, and affecting food supplies for California and beyond. We will also examine solutions that may be within reach for Central Valley residents. 

Part of its 7 million people is on the front lines of climate change, and as you will learn through this blog series, what happens in the valley doesn’t stay in the valley. 

What climate change is and will keep bringing to the Valley 

Summer in the Valley is hot. Thousands of farmworkers wake up before the sun and do physically demanding work preparing the soil, taking care of trees, or planting seeds as temperatures rise during the day. In an average year (1971-2000), the region experienced about five days of extreme heat (above 104°F or 40°C), and climate projections show that within the next 30 years, people in the Valley will likely experience a month’s worth of days with extreme heat conditions.

In 2021, however, areas around Bakersfield, Fresno, and Merced already experienced 27, 36, and 17 days with maximum temperatures equal to or above 104°F (40°C), respectively (Figure 2). As extreme heat days increase, people–particularly outdoor workers–face a greater risk of heat stroke and other heat-related health effects. Extreme heat is increasingly forcing these workers to decide between risking their health—and potentially their lives—by going to work or their livelihoods to stay safe. Higher temperatures also represent a risk for families who either don’t have air conditioning or can’t afford to pay the energy bills.

Figure 2. Daily temperature for Summer 2021 (June-August). Source: NOAA, National Weather Services (available at

In addition, they increase evapotranspiration, potentially increasing water demand—mainly from agriculture—a big part of the job market in the valley and the main source of jobs. This could mean that agriculture would depend even more heavily on groundwater, further lowering groundwater levels. Rising temperatures also mean more dry vegetation, increasing the risk of wildfires that threaten communities that ring the Valley and via smoke, which decreases the already poor air quality of the Valley. 

Precipitation is changing as well. As temperatures increase, the ratio of precipitation falling as rain vs. snow is increasing, as is the likelihood of extreme precipitation events. That means there’s more water falling in a shorter period of the year and runoff is higher, potentially causing floods. Even a bit of rain in vulnerable communities can create flooded areas that make it difficult to cross a street, get to school, or get to the bus stop (Figure 3). The risk of flooding also comes to cities and communities in the Delta region, which is where the San Joaquín River and the Sacramento River meet and go into the San Francisco Bay. Sea-level rise is also expected to affect cities like Stockton and other surrounding communities.  

Figure 3. Flooded area in a community in the San Joaquin Valley. Notice the lack of sidewalks, streetlights, paved roads, and other basic infrastructure. 

Snowpack in the Sierras has served as essential water storage in the Valley, providing water during the drier periods. However, the snowpack is projected to decrease by 25 percent within the next 30 years and will become scant at lower elevations by the end of the century. Together with the overall reduction of snowpack comes an increase in uncertainty about the capacity of water managers to rely on it. In other words, snowpack loss in the Sierras won’t be a paced, slow reduction within the next 30 years, but it will likely manifest as some years having no significant snowpack in terms of water supply. These years could be consecutive and hard to predict, reducing the ability of California water systems to rely on this form of water storage.  

In 2021 we observed similar conditions. Low snowpack and high temperatures combined with relatively low precipitation exacerbated drought conditions. In October, the record precipitation increased some of the soil moisture but was only enough to dent the current multi-year drought. Followed by an unusually dry November, 80% of the state remains under Extreme Drought conditions. We still need to wait to see the effects of December rains, but while the situation may improve, it is highly unlikely that the state will fully recover this year. The entirety of the Sacramento Valley is under an Extreme Drought category, and the situation is even more dire for the San Joaquin Valley, where virtually the entire region remains under the Exceptional Drought category (Figure 4). 

Figure 4. Drought conditions in California. The San Joaquin Valley remains under Exceptional Drought conditions. The most intense category on the U.S. Drought Monitor. 

The Central Valley 

The Central Valley of California is divided into two main regions, the Sacramento Valley in the north and the San Joaquin Valley in the south (Figure 1). The Sacramento and San Joaquin Rivers converge at the area known as the Delta, and the water flows out to the San Francisco Bay. This region in California is known as the nation’s breadbasket because of its vast agriculture that provides about a third of the vegetables and two-thirds of the fruits and nuts sold in the United States.

The Sacramento Valley is home to California’s capital, Sacramento. It drains rivers like the Feather, the Yuba, and the American River, that eventually form the Sacramento River. These rivers support almost 3 million people and around 2 million acres of irrigated agriculture. The San Joaquin Valley is a particular area of focus. It is home to roughly 4.3 million people. Half of them live in disadvantaged communities, making it the area of the state with the highest concentration of rural disadvantaged communities. On top of that, the area is home to some of the state’s most stressed ecosystems. These inequities and injustices are partly due to a history of racism and segregation that lead the region to have few socioeconomic opportunities, low water security, and high exposure to some of the country’s worst air quality. 

With over 5 million acres of irrigated farmland, agriculture is the main economic activity of the San Joaquin Valley and the largest water user in the region (87%), with the remainder used by cities (3%) and natural landscapes and wetlands (10%). Climate change may impact the San Joaquin Valley disproportionally more than other regions of California because of the potential to exacerbate some of these long-standing inequities.

Recognizing that hotter temperatures, droughts, wildfires, famine, stronger storms, rising oceans, and diseases fueled by climate change are leading to poverty and displacement worldwide, I want to focus on the frontline and vulnerable communities in the Valley. By vulnerable communities, I mean people with low incomes, fellow immigrants, farmworkers, individuals who don’t speak English, and other underrepresented communities in California’s Central Valley.

These communities experience inequities regarding access to drinking water, air quality, education, recreational opportunities, and economic activities. In fact, the situation has been horrible for decades and many people in the region have woken up day after day and spent years of their lives in these harsh conditions.

Figure 1. The Central Valley of California is divided into two main regions, the Sacramento Valley in the north and the San Joaquin Valley in the south. The Sacramento and San Joaquin Rivers converge at the area known as the Delta, and the water flows out to the San Francisco Bay. 

Wells Run Dry

As surface water became less available during the year, groundwater use increased, reducing the water table to a point too low for many private and community wells to reach it. This year alone, there have been over 950 reports of wells experiencing issues ranging from lower flows and reduced water quality to being completely unable to extract groundwater (dry wells), which represents most of the reports. While the reports are statewide, the majority are within the San Joaquin Valley (Figure 5). To deal with the lack of water, residents rely on trucking in water, buying bottled water, or getting water from luckier neighbors. Some of them are waiting for help from the Drought Assistance Program for households and water systems. Agriculture wells are also affected; some farmers either do not rely as heavily on wells, or have more resources to drill deeper wells, but this is not the case for many farmers, particularly underserved farmers. As we enter what likely will be the third year of this drought, wells will continue to fail. To make matters worse, as groundwater levels fall, water quality often also declines. 

Figure 5. Statewide Distribution of Reported Household Water Supply Shortages (left) and Household Water Supply Shortages Reported to the State by Quarter (right). Source: DWR –

In preparation for what seems to be a third year of drought, the Department of Water Resources (DWR) announced its initial zero allocation (allocation changes as water availability changes) for State Water Project (SWP) contractors. The SWP is a collection of canals, pipelines, reservoirs, and hydroelectric power facilities that delivers part of its water to 27 million people in the state and over half a million acres of irrigated agriculture. About 70% of the SWP allocation goes to residential, municipal, and industrial, and about 30% to irrigated agriculture.

This doesn’t mean that 27 million people won’t have water this year; it means that their water agencies (Figure 5) may not get some percentage of water from the SWP, and they will either need to conserve that water or get it from somewhere else. Personally, it worries me that this usually means more groundwater pumping instead of understanding that we have unsustainable water demands.

Figure 6. Water contractors served by the State Water Project. Source with an interactive map:

What happens in the Valley doesn’t stay in the Valley

While about 70 percent of people in the United States understand that climate change is happening, nearly half don’t think it affects them even when they recognize it is affecting others. Is it a lack of understanding of where the things we consume come from? Is it ignorance about the vital role of plants and animals and their ecosystems in our wellbeing? Or is it a lack of empathy? That would be something we need to work on. Many people don’t yet see the ways in which climate change will affect them. In this series, we hope you see yourself no matter where you live. 

The challenges people are facing in the Central Valley now are ones many millions more will face in the next few decades. And because of the Central Valley’s importance in producing the food on all our plates, the ways in which climate change is and will affect the region will ultimately affect us all.

Consider the current drought. It affects us all whether we recognize it or not. It is affecting our most vulnerable communities in the state, it is affecting underserved farmers, it is affecting ecosystems, infrastructure, and could affect food supplies and prices. Ultimately, the water we drink and the food that fills the plates of people from California to New York and beyond depends on the people and the climate of the Central Valley. 

What I hope I showed you today is that climate change is going to fundamentally transform how, when, and where California gets its water and that those changes have profound implications for the state, for the environment, and therefore for us. And with that comes a call to action for all of us, to be conscious about the way we live, to let our representatives know that we want to do everything we can to conserve natural resources, and for the younger generation to eventually become those leaders. In this series, we invite you to join us in seeing the challenges the Central Valley faces and exploring how we can advocate for a better future for all.


  • Educational Guide about Climate Change in the San Joaquin Valley, available in English and Spanish.
  • Peer-reviewed research about the little representation for Disadvantages Communities challenges in media, science, and policy. 
  • Challenges, errors, and solutions for integrating frontline community perspectives into climate science and policy. 
  • Documentation and analysis of interviews with disadvantaged community leaders, members, and representatives in the San Joaquin Valley. 
  • SJV Water is an independent, nonprofit news site dedicated to covering water in the San Joaquin Valley.