Urban Heat Islands: Effects on Climate Change and Potential Solutions

  1. Reduced vegetation in urban areas: vegetation helps to release water to the surrounding air and reduce the ambient air with lower surface temperature.
  2. Properties of urban materials: solar reflectance, thermal emissivity, and heat capacity influence urban heat island development as they determine how the sun’s energy is reflected, emitted, and absorbed. Solar reflectance or albedo is the percentage of solar energy reflected by a surface associated with materials color.
  3. Urban geometry: the factor that influences urban heat development, notably at night is urban geometry, referring to the dimensions and spacing of buildings within a city. Urban geometry influences wind velocity, energy absorption, and the ability to emit radiation to space. Studies often work on urban geometry called urban canyons, which is a narrow street lined by tall buildings. Tall buildings create shade, reducing surface and air temperature, but when sun energy reaches the canyon surfaces, then reflect and absorb by building walls, lowering the overall canyon albedo and increasing temperature. At night urban canyons block cooling as buildings obstructs the heat released from urban infrastructure.

Modeling and evaluation of Urban Heat Islands

  1. Shortwave radiation is the ultraviolet-visible light from the sun. Urban surfaces reflect less radiation into the atmosphere and store more of it.
  2. Thermal storage influences by the thermal properties of construction materials and urban geometry.
  3. Longwave radiation or heat radiates by buildings or other objects that absorbing shortwave radiation, especially at night.
  4. Latent and sensible heat describes by evaporation of water to humidity and convection of heat between surfaces and air.
  5. Anthropogenic heat generated by cars, air conditioners, industrial facilities, and other sources.
  6. Urban geometry in modeling defines as the sky view factor (SVF), which is the visible area of the sky from a given point on the surface.
  7. Weather and geographic location impact the phenomenon with wind and cloud cover and topography of the city. Large bodies of water can generate winds and moderate temperatures .

Real case study and results

Reducing heat urban island effect in Dallas

  1. Expand and protect urban tree cover to help cool the city and improve vegetation features of the canyons. Also, sensor observations show that temperature over the pond maintains a constant temperature day and night.
  2. Increase roof reflectivity by cool roofing to reflects solar radiation and reduces energy demand for air-conditioned buildings.
  3. Reduce paving reflectivity by pervious paving, helping to lower area temperatures by increasing evaporation, and benefits water quality by reducing temperature and removing pollutants.

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