Researchers from Stanford and other institutions reported on Mar. 17 that warmer and wetter weather linked to climate change is making disease epidemics, such as dengue fever, more likely. Their findings, published in One Earth, analyzed the connection between a cyclone and a major dengue outbreak in Peru.
The study matters because diseases like dengue, which were historically absent from the United States, have started appearing in states such as Florida, Texas, and California. The research highlights how extreme weather events can drive outbreaks of mosquito-borne diseases.
Mallory Harris, lead author of the study and postdoctoral scholar at the University of Maryland who conducted the research while at Stanford, said: "Health impacts of climate change aren't something we're waiting for. They're happening now." The team found that a 2023 cyclone and coastal El Niño event in Peru was followed by a dengue outbreak ten times larger than normal. Using statistical modeling, they estimated that about 60% of cases in the hardest-hit districts were directly caused by extreme rainfall and warm temperatures during the storm—resulting in roughly 22,000 additional illnesses.
The researchers explained that heavy rains flood low-lying areas and damage water infrastructure, creating breeding grounds for mosquitoes. Warm temperatures further accelerate mosquito breeding and disease transmission. Erin Mordecai, senior author of the study and associate professor at Stanford, said: "While we often observe large dengue outbreaks following extreme weather events, this is the first time scientists have been able to pinpoint the role of climate change and precisely measure the impact of a particular storm on dengue-one of the most rapidly-growing infectious diseases."
Stanford climate modelers Jared Trok and Noah Diffenbaugh compared precipitation data from recent decades to pre-industrial levels. They found that extreme precipitation conditions like those seen in Peru in 2023 are now 31 percent more likely than before industrialization. When combined with higher temperatures, these conditions have nearly tripled in probability.
The researchers suggest targeted mosquito control measures and vaccination campaigns could help reduce future outbreaks. Investments in urban flood resilience may also be effective. Study coauthor Andrés Lescano said: "This research provides Peru's Ministry of Health an initial estimate to quantify the specific health impacts of extreme climatic events. That can be used as a reference to advocate for greater public health investments in preparation and response." Harris added: "As extreme weather events become more frequent with climate change, we need to think strategically and act decisively to prevent mosquito borne epidemics."
