California faces a substantial and expanding risk of dengue virus transmission as climate change and urbanization create increasingly favorable conditions for disease-carrying mosquitoes, according to new research published in The Lancet Regional Health – Americas. The semi-mechanistic modelling study reveals that significant portions of the state already support seasonal dengue transmission, with risks projected to intensify and spread geographically in coming decades.
Dengue transmission risk across California by season
Percentage of state area suitable for transmission, current climate conditions
transmission area
suitable area
transmission risk
Source: The Lancet Regional Health – Americas, 2026 | Georgian Medical Journal News
Climate warming drives northward expansion of dengue risk
The modelling study, conducted by researchers at the University of California, analyzed temperature and precipitation data alongside mosquito biology to map current and future dengue transmission potential across California. According to the Centers for Disease Control and Prevention, dengue remains primarily a tropical disease, but changing climate conditions are expanding its geographic reach.
Under moderate climate change scenarios, suitable transmission areas could expand by up to 60% by mid-century, with particular increases in northern California counties previously considered too cool for sustained mosquito populations. The Central Valley and coastal metropolitan areas show the highest current risk, driven by optimal temperature ranges and increasing urbanization patterns that create mosquito breeding sites.
Aedes aegypti establishment creates transmission pathway
California’s dengue transmission risk stems from the recent establishment of Aedes aegypti mosquitoes in multiple counties since 2013, as documented by the California Department of Public Health. These invasive mosquitoes, which also transmit Zika and chikungunya viruses, thrive in urban environments and can breed in small water containers around homes and businesses.
The study’s semi-mechanistic approach incorporated detailed mosquito lifecycle parameters, including temperature-dependent development rates and survival probabilities. This methodology provides more precise risk estimates than previous climate envelope models, enabling targeted public health interventions.
Urbanization compounds climate-driven risks
Beyond temperature increases, rapid urbanization across California creates additional favorable conditions for dengue transmission. Urban heat islands can extend suitable temperature ranges for mosquito development, while increased housing density and water storage practices provide abundant breeding sites.
The research team’s projections incorporate both Representative Concentration Pathway climate scenarios and urban growth models to provide comprehensive risk assessments. According to the World Health Organization, dengue incidence has grown dramatically worldwide over the past decades, with climate change identified as a key driver of geographic expansion.
Implications for surveillance and vector control
The study’s findings highlight critical gaps in California’s current mosquito surveillance network, particularly in newly identified high-risk areas. Enhanced monitoring systems will be essential for early detection of local transmission events, as California has already documented multiple travel-associated dengue cases in recent years.
Vector control strategies must adapt to address expanded geographic and temporal transmission windows. The research suggests that traditional seasonal control approaches may prove insufficient as transmission periods lengthen and geographic ranges expand northward into previously unaffected communities.
Substantial portions of California already support seasonal dengue transmission under current climate conditions, with risks projected to expand significantly under ongoing warming and urbanization trends
— Lead researchers, University of California (The Lancet Regional Health – Americas, 2026)
Key takeaways
- 75% of California’s population lives in areas with seasonal dengue transmission potential under current climate conditions
- Transmission-suitable areas could expand by 60% by mid-century under moderate climate change scenarios
- Enhanced surveillance and vector control measures are urgently needed in newly identified high-risk regions
- Urban heat islands and development patterns compound climate-driven transmission risks
Frequently asked questions
What makes California vulnerable to dengue transmission?
California’s vulnerability stems from the recent establishment of Aedes aegypti mosquitoes in multiple counties since 2013, combined with climate conditions that increasingly support mosquito survival and virus development. Urban environments with small water containers provide ideal breeding sites for these invasive mosquitoes.
How does climate change affect dengue transmission risk?
Rising temperatures accelerate mosquito development cycles and viral replication rates, while altered precipitation patterns can create or eliminate breeding sites. The study shows that even moderate climate warming could expand suitable transmission areas by 60% across California by mid-century.
What can residents do to reduce dengue transmission risk?
Residents should eliminate standing water around homes by regularly emptying containers like flower pots, buckets, and gutters where mosquitoes breed. Using EPA-approved insect repellents and reporting unusual mosquito activity to local health departments also helps reduce transmission risk.
The research underscores an urgent need for California to strengthen its dengue preparedness infrastructure before local transmission becomes established. Successful prevention will require coordinated efforts across climate adaptation, urban planning, and public health sectors to address both current risks and projected future expansion. Early investment in enhanced surveillance systems and community education programs could prevent California from joining the growing list of previously dengue-free regions now experiencing local transmission.
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Disclaimer. This article is health journalism intended for general information and education. It is not medical advice and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your individual circumstances. Full disclaimer →
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Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD. Spotted an error? Contact the editorial team.
