As South Florida planners try to tackle escalating health risks on a warming planet, they may face a significant challenge: inconsistent temperature data.
In a new study published Wednesday, University of Miami researchers found satellite measurements that calculate land surface temperatures can underestimate air surface temperatures measured by weather stations on the ground. Those readings in South Florida's steamy fall can often be off by as much as eight or nine degrees fahrenheit.
“That's a difference of like 80 to 90,” degrees, said the study’s lead author, Nkosi Muse, a meteorologist and University of Miami researcher. “So for some people, that could be life or death.”
As Miami-Dade County — the first in the nation to hire a chief heat officer and declare a heat season — undertakes plans to address the risk, accurate information will be critical, he said.
READ MORE: It's Going To Feel Like 100 Degrees In Florida A Lot More Often, Study Finds
“If we just use land surface temperature and say that this area is super hot, we should apply all our heat mitigation efforts there, we should plant more trees there, we should weatherize homes there,” Muse said, “we may be neglecting other areas that are still really warm.”
In South Florida, where sticky humidity can amp up the feels like temperature, the National Weather Service has launched a pilot program to improve warnings. In 2023, it began alerting the public at lower temperatures based on the heat index. The changes were expanded to Broward County this year.
Issuing heat advisories
Under the new parameters, heat advisories are issued when the heat index hits 105 degrees for at least two hours. Heat warnings go out when the heat index tops 110 degrees for two hours or more.
As part of that pilot program, the Service is looking at how it collects data, said Robert Molleda, the Miami/South Florida office chief meteorologist. Rather than rely only on NWS weather stations at airports, the pilot project in Miami-Dade, Broward and Palm Breach expanded to 86 sites that include both government and nongovernment stations.
“Having as many reliable monitoring stations as possible is important to not only validate the work we're doing but to make sure we get a good sample of conditions from across the area,” Molleda wrote in an email.
Expanding those stations could also help solve the planning problem.
For the study, Muse and researchers looked at nearly a decade’s worth of data, from 2013 to 2022. Satellite information was easily available, but they struggled to find data from ground stations. Only seven had consistent data, Muse said.
“We do need a better air temperature sensor network, like that's the bottom line,” he said. “We can't just use the Miami airport because Coconut Grove, Little Haiti, Liberty City are not feeling the same heat as the airport is.”
Data reveals striking differences
And the differences were striking. While temperatures between satellite and ground monitoring lined up during clear, cooler winter days, in fall they diverged. Ground level air measurements sometimes topped satellite land surface temperatures by nearly 10 degrees.
Planners tend to use land surface measurements because it provides a far bigger scale. But while land surface temperatures are critical to forecasting weather, because it gauges energy on the surface, or drought, it’s less reliable for actual temperature, Muse said.
“Land surface temperature depends on how much radiation is hitting the surface. It depends on the cloud cover, which could affect how much radiation is hitting the surface. It depends on the actual surface that we're measuring. So grass is probably going to be a lot cooler than asphalt. So those are also things that have to be taken into account too,” he said.
In less diverse places, like the Arizona desert, the two measurements are more consistent, he said. But in South Florida, with hurricanes and sometimes torrential wet season, the land surface measurements can fail to detect bigger heat impacts.
“It may be a little easier to use land surface temperature in those places. But in a place like Miami, we have this unique dynamic climate that's always changing,” he said. “It's a little harder.”
South Florida’s dense urban area also played a factor. Muse said satellite measurements don’t do a good job of parsing the radiation that can get trapped in pavement, absorbed and steadily released.
“The radiation coming in could just kind of skews the balance of things,” he said.
And while this study used Miami-Dade Count as a test case, Muse said it’s likely other areas with similar conditions across the Caribbean will be facing the same issue and will need to address better measurements.
“Especially sensors that have quality data, that aren't ones that are just willy-nilly here recording any type of information,” he said. “They give us bad measurements, bad data and bad studies.”
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