When cities face extreme heat and humidity, the need for air conditioning increases drastically, as it both cools and dehumidifies. This puts additional strain on energy demand in urban areas, but the degree to which this demand will shift is not well understood. In this new research, CEE Professor Lei Zhao projects how temperature and humidity dynamics impact air conditioning needs, providing information that will be crucial to future energy planning in urban areas.
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When cities face extreme heat and humidity, the need for air conditioning increases drastically as it both cools and dehumidifies. This puts additional strain on energy demand in urban areas, which already face exacerbated impacts of warmer temperatures and dense populations. However, the degree to which changing trends in climate will impact a city’s overall air-conditioning related energy need is not well understood.
Professor Lei Zhao, left, and former graduate student Xinchang 'Cathy' Li. After graduating from CEE in 2025, Li joined the Pacific Northwest National Laboratory as a postdoctoral fellow.
Photo courtesy Lei Zhao
New research led by CEE Associate Professor Lei Zhao and former CEE graduate student Xinchang “Cathy” Li projects how evolving energy demand will change with increasingly prevalent humid heat in cities. Their work specifically focuses on the impact of humidity and the energy burden of increased air conditioning use associated not only with indoor cooling, but dehumidification.
By coupling an updated urban building energy model with a global Earth system model, Zhao and his collaborators projected how changing temperature and humidity dynamics will impact air conditioning needs. Their findings predict that urban dehumidification energy demand will rise by 47% globally under a high emission scenario. Additionally, their work showed that humidity amplifies temperature sensitivity in a way that is more extreme than heat alone, leading to peak AC use on humid days that is three times greater than those of simply dry heat.
Even with overall trends pointing to an increase in energy, the researchers recognize that the change in humidity’s contribution to AC energy demand varies drastically by region. By the end of the century, dehumidification’s share of total air-conditioning demand increases across 59 percent of global urban area and decreases across 36 percent, resulting from different local combinations of warming, humidification, and drying.
The study’s findings suggest that accounting for humidity dynamics in urban energy planning and infrastructure development is becoming more critical across the globe, especially for rapidly urbanizing Global South. By accounting for the impacts of future climate trends now, Zhao and his collaborators hope their work will help foster resilient living environments for urban residents in the future.