Two centuries and 500 studies later, more research needed on urban climate and weather

Almost 200 years ago, Luke Howard observed an unusual phenomenon: the urban center of London was roughly three degrees warmer than its more rural surroundings. A pharmacist by training and an amateur meteorologist by interest, he also noted that the cause was human in nature. People in the city were burning more fuel in higher concentrations than their country counterparts, and the resulting ash and soot were also contributing to the city's air pollution. He authored the first book on urban climatology, The Climate of London, in 1833. Since then, researchers have probed how urban life may influence weather and climate — what have they learned?

Based on observations and modeling, an international collaboration reviewed more than 500 studies to better understand different aspects of the impact of urbanization on regional climate and extreme weather such as the devastating 2021 floods that killed hundreds in Zhengzhou city and New York.

They published their results on January 25 in Advances in Atmospheric Sciences.  

“There are still a lot of unknowns and uncertainties in the physical mechanisms of urbanization impacts and deficiencies in the modeling and analysis tools,” said paper author Cenlin He, project scientist, National Center for Atmospheric Research. “To shed light on future research directions, we need to review the recent progress of urbanization and its influence on weather and climate and to summarize the current uncertainties, knowledge gaps, and challenges on this topic.”

The scientific literature on urban climatology is extensive, He said, but the uncertainties and deficiencies in commonly used methods are not well understood. 

“We summarized the major research gaps and challenges in our understanding of the impacts of urbanization and provide our perspective and recommendations for future research priorities and directions,” said paper lead-author Yun Qian, senior scientist and Lab Fellow at US Department of Energy's Pacific Northwest National Laboratory (PNNL).

The researchers found that, across the literature, the current understanding of urban processes related to climate and weather and their associated interactions with other Earth system components is limited. While meteorological stations in urban areas around the globe are used to make key measurements, they are not standardized, and not all of them are able to make observations truly representative of the region.

For example, Qian said, standard meteorological stations tend to be located where they can be easily accessed, such as city parks. While the location has advantages, the station’s humidity and temperature measurements will be different than how those variables manifest around skyscrapers just a block away. He also noted that the station measurements do not reflect the social and cultural variability of different regions.

Another key issue, according to the researchers, is a lack of communication in the scientific community, between those making observations and those conducting modelling.  

“Modeling studies can provide information for urban hotspots and potentially best places to employ measurements, while measurements can guide the development and improvement of urban model parameterizations,” said paper author TC Chakraborty, staff scientist at PNNL and a recent graduate from Yale University. “A better observation-model integration is needed to make progress in urban studies.”

In addition to better connections in the scientific community, the researchers also emphasized improved communication between the scientific community and end users, such as stakeholders and policymakers.

“Platforms and opportunities that promote connections between scientists and end users, such as stakeholders and policy makers, are needed,” Cenlin He said. “Mutual understanding between scientists and end users is beneficial for developing or improving urban application tools and, ultimately, fostering actional urban science.”

Other contributors include Jianfeng Li and L. Ruby Leung, Pacific Northwest National Laboratory; Dan Li, Department of Earth and Environment, Boston University; Chandan Sarangi, Indian Institute of Technology; Fei Chen, National Center for Atmospheric Research; and Xuchao Yang, Zhejiang University. The U.S Department of Energy Office of Science, Biological and Environmental Research supported this research as part of the Regional and Global Modeling and Analysis program, the Multi-Sector Dynamics Modeling program and the Earth System Model Development program.