The 4th Climate Change Assesment

May 13, 2021 | 0 comments

Catagories: Climate Change

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, the southern portion of California’s Central Valley, is surrounded by the Sierra Nevada, the Southern Coastal Range, and the San Francisco Bay Delta, and it spans eight counties hosting roughly 4.3 million habitants.

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 quality. Heat stroke, valley fever, and conditions related to low 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 of rural communities in the San Joaquin Valley the most vulnerable to climate change in California.

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, that is by far the most productive agricultural region in the United States. Some of the most economically valuable commodities are seriously threated by some early climate change effects, including reduced chill hours, water scarcity, and extreme heat. Small farmers, including disadvantaged and minority farmers, are the most impacted by climate change because they are the least resilient. However, this agricultural identity presents an outstanding opportunity to mitigate climate change by adapting agricultural techniques.

Many of the climate mitigation opportunities offered by the San Joaquin Valley are related to disadvantaged communities and agriculture. To decrease the economic risks that farmers may face under climate change, a diversified land use portfolio will likely bring income opportunities in concert with agriculture and related sectors. Many of the opportunities to increase climate resilience in the San Joaquin Valley can be addressed with multiple beneficial frameworks that can simultaneously benefit agriculture, ecosystems, communities, and cities. In what follows, some highlights of the potential climate change impacts in the San Joaquin Valley along with policy recommendations are presented.


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 (0.56 °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.
  • Snowpack serves as essential water storage in the San Joaquin Valley, providing water during the drier season. Snowpack is reducing gradually at high elevation 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 projections show an increase in intensity, with an average 6 percent increase in the fraction of precipitation falling from November to March. This translates into longer dry seasons that may require replacement by increased groundwater pumping.
  • 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 subsidence, droughts and their associated excessive pumping, wildfires, and floods. 

  • Changes in groundwater levels due to subsidence (resulting from excessive pumping) 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 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.
  • If unregulated, groundwater replacement for surface water losses may increase the pervasive groundwater overdraft, compromising water reserves to cope with future droughts. Higher salinity concentrations in the reduced groundwater reserves and soils in the San Joaquin Valley may accelerate degradation of pumping equipment, which increases challenges for farmers, irrigation districts, and utility companies. Such challenges extend to districts 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 most rural disadvantaged communities lack access to basic services such as safe, reliable, and affordable drinking water, sewage, and health care, making of them the least resilient in California. Climate change is already disproportionately exacerbating their vulnerabilities, including water insecurity and extremely low air quality.
  • Poor drinking water quality will be exacerbated by more frequent droughts, such as the 2012 – 2016 drought when hundreds of wells dried, and hundreds of thousands of San Joaquin Valley residents lost water security. If enough investments in infrastructure are not implemented, thousands of households will continue struggling economically to purchase bottled water to meet their water needs.
  • Tribes are losing access to fundamental environmental resources due to overexploitation, land use change, and more frequent extreme climatological events. Climate change will reduce more their access to cultural raw materials to fulfill their traditions and ways of life.
  • Many families in the San Joaquin Valley rely on agriculture for 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.
  • Education is already negatively affected by environmental conditions such as flooding, high temperatures, poor drinking water quality, and air quality, and their effects will only increase with climate change.


The human health and well-being impacts of climate change on the general population will likely increase, these include worsening air quality caused by due to drought, wildfire, and some agricultural activities, heat-related deaths and illnesses, and illness caused by poor water quality. 

  • 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 will be exacerbated with more frequent and intense droughts. Current health services are insufficient, and climate change is increasing the necessity of emergency attention.
  • The COVID-19 impacted more dramatically disadvantaged communities in the San Joaquin Valley with chronic and extremely low air quality, showing the insufficient health resources for such emergencies that may increase with climate change. Chronic diseases, infectious diseases, and inadequate access to clean air and water will be exacerbated by climate change.


The agricultural and urban footprint on the San Joaquin Valley is exacerbated by the onset of climate change, and it 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 changes 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, 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 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 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 access to farm labor.

  • Crop yields are sensitive to changes in temperature and water stress, particularly for tree crops. Changes in the seasonality are affecting the blooming of perennial crops, 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 to achieve sustainable goals may limit such buffer resource used during drier years.
  • Dairies and beef cattle will suffer from increased water stress for irrigated feed crops which will likely compete with higher value crop commodities. Grazelands may move in elevation into the foothills but limited by land ownership.
  • In the absence of target programs, small farmers, including most Hmong, Latino, and African American, will be among the most vulnerable to climate change due to their decreased capacity of adaptation.
  • Climate change, combined with urbanization, regulation, and overexploitation of resources, will have a dramatic impact in the agricultural sector of California, with a ripple effects in the communities that depend on it. Food security in California is not compromised, but the state may need to reduce the exportation.


Adaptation and mitigation strategies

Infrastructure in the San Joaquin Valley needs mitigation and adaptation strategies that include flood management, storing water in the soil, controlling subsidence, and widely adopting zero-carbon technologies.

  • Investing in management of aquifer recharge projects to expand the current water storage capacity can allow to capture the water generated by the more frequent extreme storms and by the more intense snow melting.
  • Eliminating, reducing, or regulating the main contributors to climate change in the San Joaquin Valley, including but not limited to fracking oil wells, natural gas peaker-plants, and the transportation sector, will dramatically improve air, water, and health quality and mitigate climate change. However, those changes must be well planned to avoid creating new socioeconomic inequity.
  • Replacing polluting sources with zero-carbon-emission technologies will promote new local infrastructure development, will reduce users’ utility bills, and contribute to align faster with California policies.
  • Making local energy grids for generation and storage more resilient and build new ones, and planning for the extreme weather and disaster events (for example, heatwaves and wildfires) will provide energy security across the San Joaquin Valley.


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 more adequate planning.

  • Creation of buffers near disadvantaged communities may help bring environmental justice, and the 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.
  • Programs to incentivize the adoption of solar energy and energy storage in disadvantaged communities can help improving local quality of life by providing energy security and employment opportunities.
  • Funding for grassroot organizations and local initiatives to foment local planification and educational community outreach increases resilience of disadvantaged communities in emergencies and extreme weather events, and provides a background to understand local air and water quality issues. These programs must target adults and children, and include advocacy and education. Funding scientific community-participatory research, especially in disadvantaged communities and tribes, furthers the usefulness of research and policy.
  • Increasing underrepresented minority researchers and including citizen science contributes toward more robust planification, since more diverse perspectives are considered. Developing transdisciplinary frameworks that include monitoring of ecological impacts of climate change and land use can serve as well to address some of the inequitable socioeconomic patterns in the San Joaquin Valley.


The San Joaquin Valley ecosystems require more adequate planification 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 under an ecological framework may increase agricultural yield using natural predators for pests to reduce pesticide use. Holistic planned grazing to ensure land regeneration and plant populations will lead to more resilient ecosystems.
  • River ecosystems will benefit from enforcing management plans that include detailed harvest management records for endangered, invasive, and ecologically and commercially beneficial fish 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 levees near riparian forests will 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 the ecosystem resilience and mitigate some climate change impacts.
  • Urban buffer zones, corridors, and phantom roads to attenuate the frequency and intensity of human activity near sensory danger zones.


Agricultural climate change mitigation will benefit from planned changes in crop decisions, optimized and equitable land use and water allocations, and the use of new technologies. To avoid creating inequity, adaptation strategies must consider potential negative externalities such as effects of crop decisions on employment.

  • Adaptation to climate change may accelerate the existing trend towards more technical and data-driven agriculture. Public policies favoring more transparent data exchange may benefit farmers.
  • Climate adaptation from agriculture may continue to require public program assistance in order to further participation from the agricultural sector in mitigating climate change.
  • In-farm managed aquifer recharge can bring opportunities to create multi-benefit projects, particularly during floods, and diversify the agriculture income sources, decreasing economic risk.
  • 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 conservation agriculture, including smart use of pesticides, improving soil health, and increase soil carbon sequestration.
  • Repurposing land and diversifying farmland income will new economic activity for farmers, decreasing their economic risk, currently associated to extreme weather events and global price trends.


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

  • Fomenting cleaner energy sources for heating and cooling, including industry and houses, will reduce local greenhouse gas emissions and improve air quality in the San Joaquin Valley.

Strategically repurposing of farmland into other economic activities may help achieving groundwater sustainability, ameliorate the effects of surface water deficits, and maintaining economic and social prosperity in the San Joaquin Valley.

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