4. PLANNING & DESIGN FRAMEWORK

Urban Heat Island Effect

With urban development surfaces that were soft, permeable, and moist are turning into impermeable and dry surfaces. This development of infrastructure has led to urban heat islands and result in warmer temperatures as compared to their rural surroundings.

How Do Urban Heat Islands Form?

Reduced Vegetation in Urban Areas

Trees and vegetation provide shade and helps to reduce surface temperatures. Plants release water into the atmosphere and reduce ambient heat this process is called evapotranspiration. Urban areas consist of impervious surfaces like roads, sidewalks, roofs, and parking lots. With growth in urban areas vegetation is further reduced resulting in lesser shade and moisture that can keep urban areas cool. Hard, man made built up surfaces contribute to increase in air temperatures. (U.S. Environmental protection agency. 2008)

Properties of Urban Materials

There are different types of urban materials, they determine to what extent the suns energy is reflected, absorbed, and emitted. For example, darker surfaces have lower reflectance value of solar heat as compared to lighter surfaces. Built up materials in the urban setting have a lower albedo as compared to material in rural settings. Urban areas as a result absorb the suns heat more and reflect less. Absorbing of heat increases surrounding and surface temperatures causing urban heat.(U.S. Environmental protection agency. 2008)

Urban Geometry

Urban geometry refers to the dimensions, spacing and height of buildings and between buildings. In urban areas structures are often partially or fully obstructed by other neighbourhood structures, buildings and objects, reducing their ability to release heat back into space. During the night the air is warmer above urban centres. Narrow buildings lined by buildings on either side are called Urban Canyons. For canyons during the day, tall buildings provide shade on the streets and reduce surface heat, but when the sun does affect the heat gets absorbed by buildings as well, increasing temperatures. (U.S. Environmental protection agency. 2008)

Anthropogenic Heat

Anthropogenic heat refers to heat produced by activities of humans. This includes energy required for heating, cooling, running of appliances, and industrial process including transportation. With increase in Urban activity more heat is produced.

Weather.

Clear skies as compared to cloudy skies cause an increase in temperatures because these conditions relate to more sunlight reaching the surface. Increasing the heat island effect. Strong winds and cloudy skies cause a decrease in temperatures.

Geographic location

Location, topography and climate play a major role in determining the Urban Heat Island effect. Large bodies of water for example keep temperatures under moderation and the winds created push the heat away from cities. (U.S. Environmental protection agency. 2008)

Need to mitigate Urban Heat Island Effect. Energy Consumption

Due to increase in temperatures there is n elevated need for cooling and adds pressure on the electricity grid. Offices and homes use increase the use of cooling systems, land appliances For increase every 1°F demand for electricity also increases by 1.5 to 2 percent. Annually 5-10 percent demand for electricity is used to compensate because of the Urban Heat Island.(U.S. Environmental protection agency. 2008)

Air Quality and Greenhouse Gases

Higher temperature increase demand for energy which in turn leads to more air pollution and increase in greenhouse gas emissions. Air pollution is a cause for many human health problems as well as complex air quality like acid rain, and also contributes to climate change at a global level. (U.S. Environmental protection agency. 2008)

Human Health and Comfort

Urban heat island leads to increase in temperatures during the day and reduced cooling at night and higher air pollution, affecting human health overall. It causes a general feeling of discomfort, respiratory problems, cramps due to heat and exhaustion, non-fatal heat strokes and mortality because of heat. Sensitive populations of people (Children and elders) with existing health issues are more vulnerable and at higher risk caused by heat waves.

Water Quality

Roof tops and pavements in urban areas have higher temperatures due the the Urban Heat island effect and this heat is transferred into the storm water runoff. This causes a rise in temperatures in ponds, streams, lakes and oceans, this affects aquatic life forms and their metabolism and reproduction.

Dues to these impacts it is necessary to find solutions to reduce the Urban Heat Island effect. There are a lot of strategies that are developed to reduce these impacts and cool down urban areas. (U.S. Environmental protection agency. 2008)