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<p>This study evaluates the role of precipitation in mitigating Urban Heat Island Intensity (UHII) and Land Surface Temperature (LST) in the megacity of Tehran (Iran) over the period 2000-2022. Nighttime MODIS imagery, ERA5-Land reanalysis data, and synoptic station observations were utilized, with 22 precipitation events (precipitation &gt; 10 mm and cloud cover &lt; 10%) selected for analysis. UHII was quantified using the Pixel-based Urban Heat Island Index (PUHII) before and after precipitation events and analyzed through ANOVA, Tukey, and SEA statistical tests. The results indicate a significant reduction in mean UHII following precipitation, decreasing from 3.72 to 2.85&#xa0;°C. Additionally, the mean Surface Skin Temperature (Skt) exhibited a substantial decline in the days following precipitation, with the lowest recorded value on the second day post-event, reflecting a decrease of 3.95&#xa0;°C compared to the day before precipitation. The spatial extent of high-intensity UHII zones (4–8&#xa0;°C) decreased markedly, while moderate-intensity zones (0–4&#xa0;°C) expanded, with these changes being statistically significant. Despite the reduced UHI disparity across regions, a decline in Moran’s I index suggests diminished spatial autocorrelation in temperature distribution post-precipitation. These findings highlight precipitation as a natural mechanism for alleviating urban heat, particularly in densely built and poorly ventilated areas. The results provide a foundation for climate policy formulation, heat-resilient urban design, and the development of green infrastructure strategies in semi-arid megacities.</p>

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Mitigating urban heat: the role of precipitation in modulating surface temperature and Heat Island intensity in Tehran, Iran

  • 期刊论文

  • 发表日期：

    2026年5月11日

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  • Gh. R. Roshan,
  • A. A. Saman,
  • M. Ahmadi,
  • S. W. Grab

摘要

This study evaluates the role of precipitation in mitigating Urban Heat Island Intensity (UHII) and Land Surface Temperature (LST) in the megacity of Tehran (Iran) over the period 2000-2022. Nighttime MODIS imagery, ERA5-Land reanalysis data, and synoptic station observations were utilized, with 22 precipitation events (precipitation > 10 mm and cloud cover < 10%) selected for analysis. UHII was quantified using the Pixel-based Urban Heat Island Index (PUHII) before and after precipitation events and analyzed through ANOVA, Tukey, and SEA statistical tests. The results indicate a significant reduction in mean UHII following precipitation, decreasing from 3.72 to 2.85 °C. Additionally, the mean Surface Skin Temperature (Skt) exhibited a substantial decline in the days following precipitation, with the lowest recorded value on the second day post-event, reflecting a decrease of 3.95 °C compared to the day before precipitation. The spatial extent of high-intensity UHII zones (4–8 °C) decreased markedly, while moderate-intensity zones (0–4 °C) expanded, with these changes being statistically significant. Despite the reduced UHI disparity across regions, a decline in Moran’s I index suggests diminished spatial autocorrelation in temperature distribution post-precipitation. These findings highlight precipitation as a natural mechanism for alleviating urban heat, particularly in densely built and poorly ventilated areas. The results provide a foundation for climate policy formulation, heat-resilient urban design, and the development of green infrastructure strategies in semi-arid megacities.