Seasonal hysteresis of surface urban heat islands

Gabriele Manoli, Simone Fatichi, Elie Bou-Zeid, Gabriel G. Katul

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Temporal dynamics of urban warming have been extensively studied at the diurnal scale, but the impact of background climate on the observed seasonality of surface urban heat islands (SUHIs) remains largely unexplored. On seasonal time scales, the intensity of urban-rural surface temperature differences (ΔTs) exhibits distinctive hysteretic cycles whose shape and looping direction vary across climatic zones. These observations highlight possible delays underlying the dynamics of the coupled urban-biosphere system. However, a general argument explaining the observed hysteretic patterns remains elusive. A coarsegrained model of SUHI coupled with a stochastic soil water balance is developed to demonstrate that the time lags between radiation forcing, air temperature, and rainfall generate a ratedependent hysteresis, explaining the observed seasonal variations of ΔTs. If solar radiation is in phase with water availability, summer conditions cause strong SUHI intensities due to high rural evaporative cooling. Conversely, cities in seasonally dry regions where evapotranspiration is out of phase with radiation show a summertime oasis effect controlled by background climate and vegetation properties. These seasonal patterns of warming and cooling have significant implications for heat mitigation strategies as urban green spaces can reduce ΔTs during summertime, while potentially negative effects of albedo management during winter are mitigated by the seasonality of solar radiation.

Original languageEnglish (US)
Pages (from-to)7082-7089
Number of pages8
JournalProceedings of the National Academy of Sciences of the United States of America
Volume117
Issue number13
DOIs
StatePublished - Mar 31 2020

All Science Journal Classification (ASJC) codes

  • General

Keywords

  • Cities
  • Hysteresis
  • Seasonality
  • Surface temperature
  • Urban heat island

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