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<p>Urbanization in tropical coastal cities exacerbates the impacts of heatwaves (HWs) by modifying land-sea breeze dynamics and thermal environments. This study investigates these interactions in Colombo, Sri Lanka, using the Weather Research and Forecasting (WRF) model coupled with an Urban Canopy Model (UCM) and Local Climate Zone (LCZ) classification. Two numerical experiments were conducted: one with current urban land use and another where urban areas were replaced by cropland land use. Simulations, validated against observational data from three meteorological stations, demonstrate high accuracy in air temperature (RMSE = 0.6&#xa0;°C, <i>r</i> = 0.92) and wind speed (RMSE = 1.4&#xa0;m s<sup>⁻</sup>¹, <i>r</i> = 0.96). Daytime urban heat islands (UHIs) intensify thermal contrasts, with urban temperatures exceeding no-urban areas by &gt; 2.5&#xa0;°C, amplifying land-sea pressure gradients and strengthening onshore winds (&gt; 2&#xa0;m s<sup>⁻</sup>¹). Enhanced sensible heat flux (&gt; 400&#xa0;W m<sup>⁻</sup>²) over impervious surfaces deepens the boundary layer (up to 1500&#xa0;m) and drives vertical updrafts (&gt; 2&#xa0;m s<sup>⁻</sup>¹), promoting cloud formation and inland penetration of sea breezes. Nighttime UHIs (&gt; 1&#xa0;°C) suppress land breezes, sustaining residual onshore flow and shallow thermal gradients, while weak nocturnal updrafts (~ 0.3&#xa0;m s<sup>⁻</sup>¹) reflect lingering urban heat retention. Urban-induced pressure deficits ( &lt; − 0.2&#xa0;hPa) and potential temperature anomalies (2&#xa0;K) destabilize the lower atmosphere, broadening mixed-layer depths and enhancing convective instability. LCZ-based analysis reveals that dense urban cores excessively amplify these feedbacks. The results show that sea breeze enhancements are insufficient to mitigate UHI driven temperature extremes, as urban heat aggregation outweighs cooling benefits. The study emphasizes the need for climate-resilient planning, including optimized ventilation corridors, green infrastructure, and building-height regulations, to mitigate HW impacts.</p>

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WRF-UCM simulations of urbanization impacts on land–sea breeze circulations during three heatwaves in Colombo, Sri Lanka

  • 期刊论文

  • 发表日期：

    2025年9月27日

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  • K. L. Thisara Sathsara,
  • Nobuyasu Suzuki,
  • Hiroyuki Kusaka

摘要

Urbanization in tropical coastal cities exacerbates the impacts of heatwaves (HWs) by modifying land-sea breeze dynamics and thermal environments. This study investigates these interactions in Colombo, Sri Lanka, using the Weather Research and Forecasting (WRF) model coupled with an Urban Canopy Model (UCM) and Local Climate Zone (LCZ) classification. Two numerical experiments were conducted: one with current urban land use and another where urban areas were replaced by cropland land use. Simulations, validated against observational data from three meteorological stations, demonstrate high accuracy in air temperature (RMSE = 0.6 °C, r = 0.92) and wind speed (RMSE = 1.4 m s⁻¹, r = 0.96). Daytime urban heat islands (UHIs) intensify thermal contrasts, with urban temperatures exceeding no-urban areas by > 2.5 °C, amplifying land-sea pressure gradients and strengthening onshore winds (> 2 m s⁻¹). Enhanced sensible heat flux (> 400 W m⁻²) over impervious surfaces deepens the boundary layer (up to 1500 m) and drives vertical updrafts (> 2 m s⁻¹), promoting cloud formation and inland penetration of sea breezes. Nighttime UHIs (> 1 °C) suppress land breezes, sustaining residual onshore flow and shallow thermal gradients, while weak nocturnal updrafts (~ 0.3 m s⁻¹) reflect lingering urban heat retention. Urban-induced pressure deficits ( < − 0.2 hPa) and potential temperature anomalies (2 K) destabilize the lower atmosphere, broadening mixed-layer depths and enhancing convective instability. LCZ-based analysis reveals that dense urban cores excessively amplify these feedbacks. The results show that sea breeze enhancements are insufficient to mitigate UHI driven temperature extremes, as urban heat aggregation outweighs cooling benefits. The study emphasizes the need for climate-resilient planning, including optimized ventilation corridors, green infrastructure, and building-height regulations, to mitigate HW impacts.