Texas Tech University

Sandip Pal Studying Urban Heat's Effects on Weather in Smaller Cities

Glenys Young

June 30, 2021

Lubbock will be the Texas Tech faculty member’s laboratory for the next year.

“Hot town, summer in the city” is not just the start of a hit song, it's a scientific fact. But unlike the town in The Lovin' Spoonful's 1960s classic, most cities don't cool down at night – particularly when compared to the rural areas around them – and it's a year-round problem. In fact, the amount of heat those cities emit can even affect the weather.

Since cities have surface structures like asphalt, steel and brick rather than the natural environment of rural areas, they absorb and store more heat. Accordingly, they don't cool down as readily as rural areas after sundown. Cities, therefore, are what scientists call urban heat islands (UHIs), and the difference between the temperature of the city and that of its surrounding countryside is a measure known as UHI intensity.

The phenomenon has been studied widely in major metropolitan areas, where heat can affect things like cloud formation, rainfall patterns and even the dispersion of pollutants and gases that regulate air quality. But what about smaller cities?

Sandip Pal
Sandip Pal

That is one of the questions Sandip Pal, an assistant professor of atmospheric science in Texas Tech University's Department of Geosciences, hopes to answer. Thanks to a $335,981 grant from the National Oceanic and Atmospheric Administration (NOAA), Pal is studying how the heat from one smaller city – Texas Tech's home of Lubbock – affects the weather of a broader region.

“The UHI intensity for small cities remained unexplored,” said Pal, who studied the UHI intensity for Paris, France, and its effect on atmospheric boundary layer dynamics when he was a postdoctoral scholar in Ecole Polytechnique. “We are convinced that small cities matter, as these changes also exist for small cities.”

Those with only a few hundred thousand residents, rather than millions, have less infrastructure to store heat. But multiple factors influence UHI intensity, including how drastically or smoothly infrastructure transitions into vegetation, the prevailing weather conditions, the number of tall buildings and the differences in soil moisture conditions between urban and rural areas.

Another compounding factor is wind – something Lubbock has no shortage of. When wind blows the hotter air from cities out into rural areas – a process called urban heat advection (UHA) – how does that affect the temperature distribution? Weather forecasting models currently have trouble assessing advection under different weather conditions and in different seasons – something Pal hopes to address through his research.

“Our inability to predict the future course of UHI intensity for different types and sizes of urban areas around the world remains one of the primary sources of uncertainty in our understanding of meteorological processes in the atmosphere over urban areas,” Pal said. “Meanwhile, the number of people living in urban areas around the world is projected to reach 68% by 2050; thus, better forecasts over these areas are vital.”

From early 2022 through spring 2023, Pal's team in the Boundary Layer Meteorology research group will compare results from weather forecasting models against the observations collected under widely varying weather conditions using weather balloons, state-of-the-art light detection and ranging (lidar) instruments and available satellite measurements of surface temperature.

“We will be able to establish the quantitative aspects of the UHI for different wind patterns that have not been considered yet in UHI forecasts,” Pal said. “More fundamentally, this project will create pathways for interpretation of the UHI over any city.”

While Pal notes an unusually wet or cool year could affect the research's initial findings, data collection is expected to continue past the end of this grant period for broader, more inclusive results in the future.

“This makes the study of meteorological processes so interesting,” he said. “The atmosphere is our laboratory, which is an uncontrolled environment – unlike controlled laboratory experiments. Thus, we can understand both the regular behavior and perturbed conditions of the atmosphere and associated meteorological processes by conducting both long-term measurements and field campaigns, respectively.

“This study will be a first-of-a-kind investigation for UHI over a small city using a combination of ground-based measurements, numerical simulation and satellite measurements. But plenty of opportunities exist to extend this study and explore the findings for other small cities in the U.S. Once we have gathered the basic principles on the UHA and UHI of Lubbock, we will be able to investigate the same for cities located in other climate regions.”

Pal anticipates the research will have tangible effects, facilitating better forecasts for heat extremes, helping the public avoid excessive heat-related hazards and providing important information for outdoor events, like playground and park outings.

“This work will provide new observations that will help improve operational forecasts of urban heat while establishing the fact that small cities require better urban planning and risk management than is currently present,” Pal said. “I am extremely excited to carry it out!”

His collaborators on the research are Mark Conder of the National Weather Service's Weather Forecast Office in Lubbock and Temple R. Lee and Michael Buban of the NOAA Air Resources Laboratory's Atmospheric Turbulence and Diffusion Division and the Cooperative Institute for Mesoscale Meteorological Studies.