Urban Heat Islands

An Urban Heat Island (UHI) is a portion of an urban or metropolitan area whose temperature is much higher than its rural counterpart due to excessive human activity. The temperature difference is typically observed at night and when winds are light. When the summer and winter seasons are at their peak, the UHI is observed. Additionally, the term heat island is employed. Generally, such expressions are used to describe any place with higher temperatures than the surrounding area, but they typically apply to areas with a high concentration of human activity.

The urban heat island is caused by the heat that is trapped between concrete structures. The variance in temperature might range between 3 and 5 degrees Celsius.

Cities are Warmer Than Rural Regions

It has been noticed that areas with more vegetation enjoyed cooler temperatures than those with less vegetation. Green vegetation such as plants, trees, and forests have a significant role in mitigating the occurrence of urban heat islands. The green cover of plantations, farmlands, woods, and trees is greater in rural areas than in urban areas. Transpiration is the process through which plants regulate their temperature through transpiration. The primary source of Urban Heat Island is the urban environment. The frequent development of high-rise buildings, roads, parking lots, paved surfaces, and public transportation lines has hastened the occurrence of urban heat islands. It occurs with black or dark-colored objects. Typical urban building materials include glass, bricks, cement, and concrete.

Causes of the Urban Heat Island Effect

There are numerous elements that contribute to the UHI effect. For instance, dark surfaces absorb far more solar heat and radiation than their lighter counterparts, which explains why roads, pavements, and building roofs in urban regions see an increase in high temperatures compared to their counterparts in suburban and rural locations. The reason for this is because the materials usually utilised in metropolitan areas for pavement and roofing, such as concrete and asphalt, have significantly different thermal bulk qualities, such as heat capacity and thermal conductivity, than the rural areas that surround them. Consequently, metropolitan areas frequently experience higher temperatures than the surrounding rural areas.

Multiplication of construction projects: The rise of cities requires carbon-absorbing materials, such as asphalt and concrete, for the construction of simple urban residences to Complex Infrastructures: They trap enormous amounts of heat, which raises urban areas’ mean surface temperatures.

Dark Surface: Numerous buildings in metropolitan areas have dark surfaces, consequently lowering albedo and increasing heat absorption.

Air conditioning: Buildings with dark surfaces heat up more quickly and require more cooling from air conditioning, necessitating more energy from power plants, which increases pollution. In addition, air conditioners exchange heat with the surrounding air, generating additional local warming. Consequently, a cascading effect adds to the growth of urban heat islands.

Built Environment: Tall buildings and their frequently accompanying small streets impede air circulation, restrict wind speed, and hence diminish any natural cooling effects. This effect is known as the Urban Canyon Effect.

Need for public transportation: Transport systems and the unrestricted use of fossil fuels also contribute to the temperature of urban areas.

Absence of trees and green spaces: Which impedes evaporation, shade, and carbon dioxide removal, all of which serve to chill the surrounding air.

Effects of the urban heat island phenomenon

The UHI influences a range of forces and elements in play as follows:

Influence on animals:

In locations with temperate climates, urban heat islands will lengthen the growth season, disrupting the reproductive strategies of native species. This is most evident in the effects urban heat islands have on the temperature of the ocean. With the temperature of nearby buildings occasionally exceeding 50 degrees, precipitation will rapidly warm, causing runoff into nearby streams, lakes, and rivers (or other bodies of water) to contribute significant thermal pollution. The thermal pollution rise has the potential to raise the water temperature by 20 to 30 degrees. The fish species inhabiting the body of water will experience thermal stress and shock as a result of the fast change in their climate’s temperature.

The urban heat islands have affected the process of natural selection. The relaxation of selection pressures such as the temporal fluctuation in food and water results in the emergence of a new set of selected forces.

Impact on climate and the weather:

UHIs can have secondary impacts on local meteorology, including the modification of local wind patterns, the formation of clouds and fog, the relative humidity, and the precipitation rates. The additional heat generated by the UHI increases the upward motion, which might lead to an increase in the number of showers and thunderstorms. In addition, the UHI creates a small low-pressure area during the day, where relatively moist air from its rural surroundings converges, presumably resulting in more favourable conditions for cloud formation. Rainfall rates downwind of urban areas have increased by between 48 and 116%. Due in part to this warming, monthly precipitation is around 28 percent higher 20 to 40 miles (32 to 64 kilometres) downwind of cities than upwind. Some cities exhibit a 51 percent increase in total precipitation.

NASA stated concerning India’s Urban Heat Islands

• NASA has found an increase in heat island occurrences in metropolitan areas of Delhi.

• The urban area of Delhi has much greater temperatures than the surrounding farmlands.

• NASA’s Ecosystem Spaceborne Thermal Radiometer Experiment (Ecostress) captured this image, which revealed a big red area over Delhi and smaller red patches over the neighbouring cities of Sonipat, Panipat, Jind, and Bhiwani.

• NASA deployed the radiometer-equipped Ecostress instrument to the International Space Station in 2018.

• Ecostress is primarily accountable for determining the temperature of plants, as well as their water needs and the climate’s effect on them.

How can Urban Heat Islands be Reduced?

• Planting trees and efforts to increase the area under green cover are the major requirements for reducing the heat load within urban areas.

• Passive Cooling for Urban Heat Island Mitigation: Passive cooling technology, a prevalent approach for creating naturally ventilated structures, can be a crucial alternative for residential and commercial buildings to combat the urban heat island.

• In the context of global warming, the IPCC report references ancient Indian architectural designs that incorporated this technology, which may be adapted for modern buildings.

• Using proper building materials is an additional approach to heat reduction.

• White or light colours should be used to paint roofs and terraces to reflect heat and prevent absorption.

• Terrace gardening and kitchen gardening ought to be encouraged.

Conclusion

In light of the above-mentioned effects, it becomes imperative to counter urban heat islands with appropriate techniques. Policymakers should prioritise preventing unplanned growth by increasing opportunities in rural areas and planning for future growth. Additional planning should incorporate passive cooling methods and ventilation setup. As a concise conclusion, growing global warming necessitates human involvement to make the planet habitable, but these interventions must be foolproof.