Scientists have developed a new way to represent the world's cities in global climate and Earth system models (GCM & ESMs), offering a more accurate picture of how urban areas are being affected by - and contributing to - climate change.
The study, funded by Natural Environment Research Council (NERC), and led by researchers at The University of Manchester, introduces a more detailed way of simulating how urban areas interact with the atmosphere inside one of the world's leading models, the Community Earth System Model (CESM), which scientists use to predict how the Earth's climate behaves now and in the future.
Until now, these large-scale climate and Earth system models have treated cities very simply, grouping them into just a few generic categories such as "high density" or "medium density". But cities differ enormously with a mix of buildings, roads, vegetation and human activity, which can significantly affect how heat is stored, released and transferred, with knock-on effects for heatwaves, air quality and energy demand. These factors are often overlooked in current climate predictions and policy decisions.
The new model, published today in the Journal of Advances in Modeling Earth Systems, integrates a detailed urban classification system known as Local Climate Zones (LCZ), which distinguishes between ten types of built environments - from compact high-rise districts to open low-rise neighbourhoods. Each environment is defined by its building height, layout and materials and allows researchers to simulate how cities exchange heat and energy with the atmosphere in much finer detail.
Lead author Dr Zhonghua Zheng, Co-Lead for Environmental Data Science & AI at Manchester Environmental Research Institute (MERI) and Lecturer in Data Science & Environmental Analytics at The University of Manchester, said: "Cities, which host more than half of the world's population, are highly vulnerable to the impacts of climate change, but they are also key to sustainable solutions. By using the Local Climate Zones approach, we can now represent the true diversity of urban areas, which is crucial for making accurate climate predictions. Improving how we simulate cities will help researchers and policymakers better understand urban heat stress and energy use, and design more effective strategies for the future."
Yuan Sun, PhD researcher at The University of Manchester, added: "Incorporating LCZs into ESMs provides a bridge for communication between the environmental model community and urban climate adaptation actors."
Tests carried out at 20 urban observation sites worldwide, including locations in France, South Korea, the United Kingdom and the Netherlands, showed that the new LCZ-based approach improved the model's accuracy in simulating key urban heat processes. These include how city surfaces release heat into the atmosphere (known as upward longwave radiation) and the heat generated by human activity, such as air conditioning (known as anthropogenic heat flux), compared with the standard urban scheme.
The study also identified where LCZ-based models could be refined to further improve accuracy.
Sensitivity experiments revealed that rooftop reflectivity has the biggest impact on sunlight and heat in cities, while the layout and shape of streets and buildings, along with roof materials, also play key roles.
Understanding these factors in urban areas could help explain why some areas get hotter than others and could guide future urban design and climate adaptation strategies.
This research appeared in the Journal of Advances in Modeling Earth Systems
Full title: Enhancing Global-Scale Urban Land Cover Representation Using Local Climate Zones in the Community Earth System Model
DOI: http://doi.org/10.1029/2025MS004934
