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Temperature and Humidity Do Not Play a Major Role in Coronavirus Spread

When the coronavirus pandemic started, people thought that hot summer temperatures would decrease its spread. While summer did not bring extensive respite, the link between COVID-19 and the weather continues to be a widely prevalent subject.

A study led by Jackson School Professor Dev Niyogi has found that temperature and humidity do not play a significant role in coronavirus spread. Image Credit: Ian Dolphin.

The connection between COVID-19 and weather is complex. Weather impacts the environment in which the coronavirus has to live before infecting a new host. But it also impacts human behavior, which shifts the virus from one host to the next.

Research headed by The University of Texas at Austin is providing a little clarity on the role of weather in COVID-19 infection. The new study found that humidity and temperature do not play a major role in the spread of coronavirus.

This suggests that whether it is cold or hot outside, the spread of COVID-19 from one person to the next relies almost totally on human behavior.

The effect of weather is low and other features such as mobility have more impact than weather. In terms of relative importance, weather is one of the last parameters.

Dev Niyogi, Study Lead and Professor, Jackson School of Geosciences and Cockrell School of Engineering, The University of Texas at Austin

The study was published in the October 26th issue of the International Journal of Environmental Research and Public Health. Co-authors of the study are Maryam Baniasad, a doctoral candidate at Ohio State University, and Sajad Jamshidi, a research assistant at Purdue University.

The research established weather as “equivalent air temperature,” which integrates humidity and temperature into a single value. The researchers then examined how this value tracked with the spread of coronavirus in various areas between March and July 2020, with their scale spanning from U.S. states and counties, to countries, regions, and the entire world.

At the state and county scale, the team also examined the link between coronavirus infection and human behavior, which involved the use of cellphone data to analyze travel routines.

The research looked at human behavior in a basic sense and did not try to link it to how the weather may have affected it. At each scale, the team modified the analyses so that differences in population did not twist the results.

Within scales, the researchers learned that the weather had virtually no impact. A comparison of weather with other parameters using a statistical metric that simplifies the relative contribution of each parameter toward a specific outcome showed that its relative significance at the county scale was below 3%, with no sign that a particular type of weather increased spread over another.

On the other hand, the data clearly revealed the impact of human behavior—and the outsized impact of individual behaviors. Going on trips and being away from home were the two main factors contributing to the spread of COVID-19, with a relative significance of around 34% and 26%, respectively. The next two crucial parameters were urban density and population, with a relative significance of around 13% and 23%, respectively.

We shouldn’t think of the problem as something driven by weather and climate,” stated Jamshidi. “We should take personal precautions, be aware of the factors in urban exposure.”

According to Baniasad, a biochemist and pharmacist, theories regarding how coronavirus would react to weather are mainly informed by studies performed in lab settings on related viruses. She added that this research shows the significance of studies that examine how the coronavirus spreads via human groups.

When you study something in the lab, it’s a supervised environment. It’s hard to scale up to society,” she added. “This was our first motivation to do a more broad study.”

Marshall Shepherd, an atmospheric sciences professor at the University of Georgia who was not part of the research, stated that the study gives vital insights about coronavirus and weather across scales.

This important work clarifies some of the innuendo about weather-COVID-19 connections and highlights the need to address science challenges at the appropriate scales.

Marshall Shepherd, Professor of Atmospheric Sciences, University of Georgia

Niyogi narrated that one of the main lessons of the pandemic is the importance of examining phenomena at the “human scale”—the scale at which humans live their everyday lives. He added that this study is an illustration of this type of viewpoint.

COVID, it is claimed, could change everything. We have been looking at weather and climate outlooks as a system that we scale down, down, down and then seeing how it might affect humans. Now, we are flipping the case and upscaling, starting at human exposure scale and then going outwards. This is a new paradigm we will need for studying virus exposure and human environmental modeling systems involving new sensing and AI-like techniques.

Dev Niyogi, Study Lead and Professor, Jackson School of Geosciences and Cockrell School of Engineering, The University of Texas at Austin

The study received funding from The University of Texas at Austin, the National Science Foundation, and NASA.

Journal Reference:

Jamshidi, S., et al. (2020). Global to USA County Scale Analysis of Weather, Urban Density, Mobility, Homestay, and Mask Use on COVID-19. International Journal of Environmental Research and Public Health.


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