Greater aridity increases the magnitude of urban nighttime vegetation-derived air cooling

Peter C. Ibsen, Dorothy Borowy, Tyler Dell, Hattie Greydanus, Neha Gupta, David M. Hondula, Thomas Meixner, Mary V. Santelmann, Sheri A. Shiflett, Michael C. Sukop, Christopher M. Swan, Michelle L. Talal, Miguel Valencia, Mary K. Wright, G. Darrel Jenerette

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


High nighttime urban air temperatures increase health risks and economic vulnerability of people globally. While recent studies have highlighted nighttime heat mitigation effects of urban vegetation, the magnitude and variability of vegetation-derived urban nighttime cooling differs greatly among cities. We hypothesize that urban vegetation-derived nighttime air cooling is driven by vegetation density whose effect is regulated by aridity through increasing transpiration. We test this hypothesis by deploying microclimate sensors across eight United States cities and investigating relationships of nighttime air temperature and urban vegetation throughout a summer season. Urban vegetation decreased nighttime air temperature in all cities. Vegetation cooling magnitudes increased as a function of aridity, resulting in the lowest cooling magnitude of 1.4 °C in the most humid city, Miami, FL, and 5.6 °C in the most arid city, Las Vegas, NV. Consistent with the differences among cities, the cooling effect increased during heat waves in all cities. For cities that experience a summer monsoon, Phoenix and Tucson, AZ, the cooling magnitude was larger during the more arid pre-monsoon season than during the more humid monsoon period. Our results place the large differences among previous measurements of vegetation nighttime urban cooling into a coherent physiological framework dependent on plant transpiration. This work informs urban heat risk planning by providing a framework for using urban vegetation as an environmental justice tool and can help identify where and when urban vegetation has the largest effect on mitigating nighttime temperatures.

Original languageEnglish (US)
Article number034011
JournalEnvironmental Research Letters
Issue number3
StatePublished - Mar 2021


  • air temperature
  • aridity
  • ecosystem service
  • urban heat
  • vegetation cooling

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • General Environmental Science
  • Public Health, Environmental and Occupational Health


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