California’s Climate Change Assessment for the San Joaquin Valley Region

May 13, 2021 | 0 comments

Catagories: Climate Change | Past

The onset of Climate change is impacting the lives of billions of people in the planet, including Californians. Extreme heat and the increasing frequency and intensity of droughts, floods, and wildfires are some of the most tangible effects for the State of California, and the state government has for decades supported science-based assessments to summarize the current knowledge. The California’s Fourth Climate Change Assessment incorporated regional reports, and a team of researchers at UC Merced led by Dr. Angel Fernandez-Bou, just released the regional report for the San Joaquin Valley

The report is available on in English and a summary is available in Spanish.




The team identified major climate-linked negative impacts for agriculture, communities, ecosystems (including water resources), infrastructure due to drought (and increased overpumping), floods and wildfires. Some of these impacts of climate change are more pronounced in rural disadvantaged communities of the San Joaquin Valley than in the rest of California.  Human health and well-being of the general population in disadvantaged communities including more heat-related deaths and illnesses, deteriorating air and water quality, and general quality of livelihood will likely arise without proper climate change mitigation strategies serving these populations. Some intensive agricultural practices and unplanned development on the San Joaquin Valley may also exacerbate negative impacts of climate change, furthering habitat loss for native species and the establishment of invasive species.  Climate vulnerabilities to agriculture include fewer winter chill hours, shifts in water availability, increased evaporative demands, and extreme heat. Reduced crop yields may also have direct and indirect effects on population in the valley’s economy and employment.

Some promising mitigation and adaptation strategies include improving flood management, replenishing aquifers, controlling land subsidence, and widely adopting carbon-neutral technologies. “The inclusion of disadvantaged communities is an essential step to bringing environmental and social justice to the San Joaquin Valley. Emergency management and health services require proper investments and adequate planning in underserved frontline communities”, says Dr. Fernandez-Bou, a UC Merced alumni from the Environmental Systems Graduate Group, a Postdoctoral scholar at the Water Systems Management Lab with professor Medellin-Azuara, and coordinating lead author. Multi-benefit approaches for to strategically repurpose land in the San Joaquin Valley and increase climate resilience are worth exploring, says professor Medellin.

The completion of the report was led and funded by UC Merced’s Water Systems Management Lab under professor Medellin and also volunteer work from coauthors. Other UC Merced lead authors graduate students Vicky Espinoza, Jose Manuel Rodriguez and Humberto Flores-Landeros, with a longer list from contributing graduate students and researchers from UC Merced and other institutions. Initial versions of the report were product an Environmental Systems graduate directed study group under professors Viers, Westerling and Medellin during the California’s Fourth Climate Assessment led by the California Energy Commission and the California Natural Resources Agency.


For a present-day Californian who crosses the San Joaquin Valley it may be challenging to visualize how the valley has changed in the last 200 years. Other regions of California, such as the Sierra Nevada to the east or the Southern Coastal Range to the west, have also changed, but they still preserve some of their timeless features. That is not the case of the San Joaquin Valley. In the XIX century, the San Joaquin Valley was the homeland of the Yokuts and Miwok, and it was covered by wetlands and ephemeral rivers. A large lake covered what today is part of Tulare, Kings, Fresno, and Kern counties. The Tulare Lake fluctuated in size every year due to varying weather conditions (from 110,000 acres to 470,000 acres, this is between 450 km2 and 1900 km2); in a normal year, it would be larger than the city of Los Angeles. At present, the Tulare Lake is no more, and the San Joaquin Valley has lost about 95 % of its original wetlands.

Wetlands of the Merced National Wildlife Refuge in February 2021. During the wet season (winter and spring), some of the few preserved wetlands are flooded with water, and millions of birds live in there or visit them. About 200 years ago, the wetlands of the San Joaquin Valley covered 20 times more area than at present. Photo by Angel S. Fernandez-Bou.

Wetlands of the Merced National Wildlife Refuge in February 2021. During the wet season (winter and spring), some of the few preserved wetlands are flooded with water, and millions of birds live in there or visit them. About 200 years ago, the wetlands of the San Joaquin Valley covered 20 times more area than at present. Photo by Angel S. Fernandez-Bou.

Highlights and findings

The San Joaquin Valley is the southern portion of the Central Valley of California. It is surrounded by the Sierra Nevada on the East, the Southern Coastal Range on the West, and the Sacramento-San Joaquin Delta on the Northwest, spanning eight counties with 4.3 million inhabitants.

The socioeconomic and environmental conditions of the San Joaquin Valley are among the most precarious in California, with more than 55 % of its population living in disadvantaged communities. Hundreds of thousands of people do not have water security, and most inhabitants suffer from chronic exposure to one of the nation’s lowest air qualities. Heat stroke, valley fever, and conditions related to poor air and water quality are common illnesses and health hazards. The effects of the onset of climate change are exacerbating all these issues, and the lack of investment in fundamental infrastructure, such as access to drinking water, sewage, green areas, grocery stores, sidewalks, public electrification, education facilities, and health services, makes rural communities in the San Joaquin Valley some of the most vulnerable to climate change in the United States.

Ecosystems of the San Joaquin Valley are among the most degraded in California. Originally a humid region with ephemeral rivers and lakes, the San Joaquin Valley has lost 95 % of its original wetlands. Most current agricultural practices compete with ecosystems for water access, and often the San Joaquin River runs nearly dry during the summer due to upstream diversions for beneficial uses.

Agriculture is the main economic activity of the San Joaquin Valley and is by far the most productive agricultural region in the United States. Some of the most economically valuable commodities are threatened by some early climate change effects, including reduced chill hours, water scarcity, and extreme heat. Small farmers, including disadvantaged and minority farmers, are among the most impacted by climate extremes in part because of their limited resources to build the needed resilience. However, agriculture presents an outstanding opportunity to mitigate climate change by adapting agricultural practices.

Many of the climate mitigation opportunities facing the San Joaquin Valley are related to disadvantaged communities and agriculture. Investing in diversified land use strategies can provide new income opportunities that can decrease the economic risks that farmers may encounter under climate change. Many of the options to increase climate resilience in the San Joaquin Valley can be addressed with multi-benefit approaches that can benefit agriculture, ecosystems, communities, and cities. This report presents highlights of the potential climate change impacts in the San Joaquin Valley along with possible adaptation and mitigation strategies.


Climate change is already affecting the San Joaquin Valley’s communities and agriculture. 

  • The San Joaquin Valley annual average maximum temperatures increased by 1 °F (0.6 °C) from 1950 to 2020, and it is projected to increase 4 °F to 5 °F (2.2 °C to 2.7 °C) by mid-century, and 5 °F to 8 °F (2.7 °C to 4.4 °C) by the end of the century. If emissions continue to rise at high rates (RCP 8.5), projections indicate that half of the San Joaquin Valley counties will have average annual maximum temperatures over 80 °F (26.7 °C) by the end of the century, which is more than an 8 °F increase compared to historical conditions.
  • Snowpack in the Sierra Nevada shas served as an essential water storage in the San Joaquin Valley, providing water during the drier season. However, snowpack is gradually decreasing at high elevations and is projected to become scant at lower elevations by the end of the century.
  • As temperature increases, earlier snowmelt will shift peak flows by 2 to 4 months by the end of the century. This shift may reduce surface water storage, increasing the mismatch between when the water is available (winter-spring) and when most of the water is used (summer).
  • Precipitation will likely be more intense, increasing the fraction of precipitation falling from November to March from 75 % (current conditions) to 80 % (by the end of the century). This translates into longer dry seasons with 20 % less precipitation in average that may lead to increased groundwater pumping to compensate the diminished surface water supplies.
  • Sea level rise increases flooding risk in Delta communities and San Joaquin County cities such as Stockton, threatening over 10,000 people. Over the past 100 years, sea level has risen 8 inches (20 cm), and it could rise 2 feet (74 cm) by mid-century and 3.5 ft (107 cm) by the end of the century.


Climate Change may accelerate deterioration of private property, canals, dams, roads, railways, and levees due to increasing land subsidence, droughts and associated overpumping, wildfires, and floods. 

  • Changes in groundwater levels due to land subsidence (sinking ground levels resulting from water overextraction) may dramatically affect the region’s infrastructure, including canals, roads, and railways. Levees protecting floodplains, cities, and farmlands will become more unstable due to prolonged droughts that promote water filtration through the soil, soil cracking, soil organic carbon decomposition, erosion, and land subsidence.
  • Faster snowmelt may also threaten dam stability, leading to increasing risk of catastrophic dam failure. Earlier snowmelt will anticipate the peak flows to earlier than when agriculture needs them, signaling the currently inadequate water storage. Combined, the effects of snowmelt shifting may reduce the freshwater that returns and stays in the San Joaquin Valley due to the limited pumping and conveyance systems.
  • Groundwater replacement for surface water losses may increase the pervasive groundwater overdraft, compromising water reserves to cope with future droughts. The Sustainable Groundwater Management Act (SGMA) enacted to prevent future overdraft is still in its early stages and some districts may not be able to fully implement sustainability plans by the 2040 time horizon.
  • Higher salinity concentrations in soil and groundwater in the San Joaquin Valley may accelerate degradation of pumping equipment, which increases challenges for farmers, irrigation districts, utility companies, and wholesalers.
  • More frequent wildfires threaten access to clean drinking water when fires affect urban supply watersheds and increase soil erosion that may move undesirable chemicals in the watershed. Wildfires can also damage the electrical system directly by burning transmission lines or indirectly by ionizing the air with smoke and ash, causing a system shutdown.


The impacts of climate change are more pronounced in rural disadvantaged communities of the San Joaquin Valley than in the rest of California. 

  • More than half of the population in the San Joaquin Valley live in disadvantaged communities, and many rural disadvantaged communities lack access to basic services such as safe, reliable, and affordable drinking water, sewage, and health care, making them some of the least resilient communities in California. Climate change is already disproportionately exacerbating their vulnerabilities, including water insecurity and extremely poor air quality.
  • Multi-year climate extremes are becoming more frequent, such as the 2012 – 2016 drought when thousands of wells dried decreasing the already poor drinking water quality. In normal conditions, thousands of households struggle purchasing bottled water, and that situation is exacerbated during droughts when some residents do not have any available water at all.
  • Tribes are losing access to fundamental environmental resources due to overexploitation, land use change, and more frequent extreme climate events. Climate change will further reduce their access to cultural raw materials to fulfill their traditions and ways of life.
  • Many families in the San Joaquin Valley rely on agriculture as their main source of income. Livelihood insecurity is increasing since agricultural productivity is threatened by more frequent extreme events such as droughts, floods, and more favorable conditions for some pests. Food insecurity and food deserts are common issues in frontline communities in the San Joaquin Valley.
  • Education access is already negatively affected by reduced school attendance and difficulted study conditions because of environmental conditions such as flooding, high temperatures, poor drinking water quality, and air quality. These effects will likely increase with climate change.


Human health and well-being of the general population will be impacted by climate change, including more heat-related deaths and illnesses, illnesses caused by poor water quality, and other issues caused by droughts, wildfire, and some agricultural activities. 

  • Higher temperatures are increasing the risk of heat-stroke and other effects on vulnerable populations and outdoor workers. Valley fever cases are more common in the San Joaquin Valley than in the rest of California, and this poorly studied illness could be exacerbated by the intensified combination of wetter conditions that allow the fungus to reproduce, and dryer, windy periods that contribute to the spread of the spores from the soil into people’s respiratory systems (dust storms). Current health services are insufficient, and climate change is increasing the necessity of emergency attention.
  • Extreme heat days are projected to increase for all San Joaquin Valley counties from current 4 or 5 extreme heat days per year to about 18 to 28 days towards mid-century, and about 24 to 68 days towards the end-of-century.
  • The COVID-19 crisis has been more impactful in disadvantaged communities in the San Joaquin Valley with chronic and extremely poor air quality, uncovering the rather lagging health services access for such communities. Chronic diseases, infectious diseases, and unsuitable air and water quality are being exacerbated by climate change.
  • Intensifying climate change is likely to increase water quality issues that inequitably impact rural disadvantaged communities. Common chemicals across the San Joaquin Valley rural disadvantaged communities include arsenic, nitrates, 1,2,3-trichloropropane (1,2,3 TCP), chromium VI, and manganese. Pathogens ( coli, Giardia, Salmonella) are also problematic in unincorporated communities and near some dairy farms.


The intensive agricultural and urban footprints on the San Joaquin Valley are exacerbating the negative impacts of climate change, which may lead to ecological collapse because of the extensive habitat loss for native species and the establishment of invasive species. 

  • Primary production will decrease with more frequent extreme temperatures, floods, and droughts, combined with land use change, affecting the production, transfer, and distribution of energy across trophic levels, and impacting ecosystem functions and services.
  • Earlier and rapid snowmelt from warmer temperatures will change flow regime and water conditions, impacting spawning times, reproductive success, and habitat suitability for many species, including native endangered fish.
  • Under climate change, natural wetlands may experience more prolonged periods of drought, disastrous floods, and increased water temperatures and evaporation rates. Combined with poor water management practices and competition with agriculture, climate change effects can lead to native population instability and to food scarcity for essential organisms such as overwintering birds and insects.
  • Urban ecosystem species undergo the combining effects of climate changes and pollution from human expansion. Expanding impervious surfaces in cities will increase heat retention leading to more prominent urban heat island effects. Land use change will increase human-animal disease transmission as urban areas overlap rural and wild environments.


Agriculture climate vulnerabilities include fewer winter chill hours, shifting water availability, and extreme heat. These threats have direct and indirect impacts such as changes in yield, crops water demand, increasing competition for water from other sectors, and reduced farm labor availability. 

  • The agricultural sector in the San Joaquin Valley supports more than 200,000 jobs per year over 8 million acres (32,000 km2), and it has successfully adapted to pests, changes in yield, and dry conditions by changing crop practices, land use, and water use decisions. Climate change will affect risk and resilience of the agriculture-dependent economy and employment. Additionally, the Sustainable Groundwater Management Act (SGMA) will have an important role on land and water use decisions, especially during droughts.
  • Crop yields, especially tree orchards, are sensitive to changes in temperature and water stress. Changes in the seasonality are affecting the blooming of perennial crops, while the decreasing number of chill hours is affecting their quality and productivity.
  • Crop water use will increase as higher temperatures increase vapor deficit and potential evapotranspiration. Higher carbon concentrations may partially offset this effect for some crops. More frequent droughts will increase the reliance on groundwater, but groundwater pumping regulations through the Sustainable Groundwater Management Act may limit such resource to drier years.
  • Dairies and beef cattle will have less water available for irrigated feed crops as they compete with higher value crop commodities. Grazelands may move in elevation into the foothills but may be limited by land ownership. Rising temperatures and more intense and frequent heatwaves increase the cattle mortality risk.
  • In the absence of target relief programs for small farmers, including most Hmong, Latino, and African American, the adaptation capacity of these groups will be hindered by climate change. Shallow wells, water restrictions, limited access to capital sources, and outdated technology and irrigation systems, threaten the economic feasibility of their diverse crops that are very important culturally and at the local level.



Adaptation and mitigation strategies

Infrastructure in the San Joaquin Valley merits adaptation and mitigation strategies that include improving flood management, replenishing aquifers, controlling land subsidence, and widely adopting zero-carbon technologies. 

  • Investing in management of aquifer recharge projects to expand the current water storage capacity allows to capture the water generated by the more frequent extreme storms and by the more intense snowmelt.
  • Reducing the impacts from major contributors to climate change in the San Joaquin Valley, such as fracking oil wells, natural gas peaker-plants, and the transportation sector, can improve air, water, and health quality while mitigating climate change. A planned transition (also known as “just transition”) via regulation and stakeholder involvement will likely reduce the potential short-term socioeconomic inequity of this process.
  • Replacing polluting sources with zero-carbon-emission technologies will promote new local infrastructure development and will align faster the energy sector with California policies.
  • Energy security across the San Joaquin Valley can be increased by building new local energy grids for generation and storage, by making the current facilities and infrastructure more resilient, and by planning for extreme weather and disaster events (for example, heatwaves and wildfires).


Inclusion of disadvantaged communities is an essential step to bring environmental justice to the San Joaquin Valley. Emergency management and health services require proper investments and adequate planning in underserved frontline communities. 

  • Creation of buffer zones (physical separation areas) surrounding disadvantaged communities may help protect local aquifers and air quality. Buffers can be used for new economic activities with positive environmental and social externalities, including renewable energy, management of aquifer recharge, green corridors to preserve habitat, and nonpolluting industries. Sustainable land management in the buffers is important to avoid increasing environmental inequities.
  • Programs to incentivize adoption of solar energy generation and storage in disadvantaged communities can provide energy security, and adequate policies can help keep employment opportunities within the communities without compromising the viability of agriculture.
  • Funding for grassroot organizations to encourage local planning increases resilience of disadvantaged communities in emergencies and extreme weather events. Educational community outreach provides a foundation in efforts to understand local air and water quality issues. These programs can be more effective when targeted for both adults and children, and when they include advocacy and “citizen science” approaches. Funding scientific community-participatory research, especially in disadvantaged communities and tribes, furthers the usefulness of the research and better informs policy.
  • Increasing the number of underrepresented minority researchers and promoting the hire of local scientists can contribute toward greater motivation to achieve solutions, more robust strategies, and more diverse perspectives.
  • Developing transdisciplinary frameworks that include monitoring of ecological impacts of climate change and land use can serve to address some of the inequitable socioeconomic patterns in the San Joaquin Valley.


The San Joaquin Valley ecosystems require more adequate planning and management to increase natural adaptation and mitigation to local and global climate changes. Climate change policies can be better informed by ecosystem research across biological scales (from cells to communities) to understand the system holistically. 

  • Modernizing agricultural practices within an agroecosystems framework may increase agricultural yield, for example using natural predators for pests to reduce pesticide use. Holistic planned grazing to ensure land regeneration and plant populations will lead to more resilient agroecosystems.
  • River ecosystems can benefit from enforcing management plans that include harvest management records for endangered, invasive, and ecologically and commercially beneficial freshwater species, and from funding for long-term monitoring research of springs, streams, and rivers using bioindicator responses to pollutants and habitat quality.
  • Strategically removing or relocating some specific levees near riparian forests can help restore natural floodplains and mitigate the impacts of extreme climatic events, increasing habitat and resource availability, and quality for native species adapted to naturally variable conditions. When properly managed, wetlands can increase ecosystem resilience and mitigate some climate change impacts.
  • Wildlife corridors and protected areas in urban environments can attenuate the frequency and intensity of human activity near sensitive ecosystems.


Agricultural climate change mitigation can benefit from planned changes in crop decisions, optimized and equitable land use and water allocations, and the use of new technologies. To avoid furthering inequity, linkages between crop decisions and employment merit consideration and more research. 

  • Adaptation to climate change may accelerate the existing trend towards more technical and data-driven agriculture. Public policies favoring more transparent data exchange can be beneficial for farmers.
  • Climate strategies involving farmland may continue to require public program assistance to incentivize participation from the agricultural sector to mitigate climate change.
  • In-farm managed aquifer recharge can bring opportunities to create multi-benefit projects, particularly during floods and droughts.
  • Mitigation strategies in agriculture include the use of solar energy for in-farm operations (for example, for pumping and irrigation) and the use of renewable energies along the supply chain including transportation, food industry, and waste management.
  • Agriculture can be used for natural habitat to increase ecosystem services and resilience to climate change, provided that some practices shift toward sustainable agriculture, including smart use of pesticides, improving soil health, and increase soil carbon sequestration.
  • Repurposing land and diversifying farmland income may bring new economic activity for farmers and communities, decreasing their economic risk, currently associated to extreme climate events in a globalized economy.


The San Joaquin Valley has extensive land that can be strategically used for multi-benefit projects that create opportunities to mitigate climate change, and to bring socioeconomic development and environmental justice. 

  • Promoting cleaner energy sources for heating and cooling, including industry, institutions and households, will reduce local greenhouse gas emissions and improve air quality in the San Joaquin Valley.
  • Strategically repurposing farmland into other economic activities may help achieve groundwater sustainability, ameliorate the effects of surface water deficits, and maintain economic and social prosperity in the San Joaquin Valley.


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