Details on Urban Heat Islands

Due to human activities, an urban heat island (UHI) is a city or metropolitan area that is much warmer than its surrounding rural areas. When the winds are light, the temperature differential is frequently greater at night than during the day. Summer and winter are when UHI is most evident. The change of land surfaces is the primary cause of the urban heat island effect.  A secondary contributor is waste heat created by energy use. As a population centre grows, its area expands and its average temperature rises. The term “heat island” is also used to any location that is hotter than the surrounding area, but it most commonly refers to human-affected areas. 

History

Luke Howard was the first to explore and describe the phenomenon in the 1810s, albeit he was not the one to name it. Throughout the nineteenth century, researchers looked at the urban environment. Between the 1920s and the 1940s, scholars in Europe, Mexico, India, Japan, and the United States investigated new approaches to understand the phenomenon in the burgeoning area of local climatology or microscale meteorology. Albert Peppler used the phrase “staedtischen Waermeinsel” in 1929, which is said to be the earliest counterpart to urban heat island.

Causes

There are several factors that contribute to an urban heat island (UHI), for example, dark surfaces absorb significantly more solar radiation, causing urban concentrations of roads and buildings to heat up more during the day than suburban and rural areas; materials commonly used in urban areas for pavement and roofs, such as concrete and asphalt, have significantly different thermal bulk properties (including heat capacity and thermal conductivity) and surface radiative properties. This changes the metropolitan area’s energy budget, resulting in greater temperatures than the surrounding rural areas.  Another key factor is the absence of evapotranspiration in urban areas (due to a lack of flora, for example). 

Diurnal Behaviour

“It is generally established that, in comparison to non-urban areas, urban heat islands boost night-time temperatures more than midday temperatures,” according to the IPCC. For example, daily maximum are 0.2 °C (0.36 °F) cooler in Barcelona, Spain, whereas daily minimum are 2.9 °C (5.2 °F) warmer in a neighbouring rural station.  According to Luke Howard’s description of the earliest report of the UHI in the late 1810s, the urban core of London was 2.1 °C (3.7 °F) warmer at night than the surrounding countryside. 

Seasonal  Behavior

Not only is the urban heat island temperature difference usually greater at night than during the day, but it is also greater in the winter than in the summer. This is especially true in snowy places, because cities tend to store snow for a shorter amount of time than rural areas (this is due to the higher insulation capacity of cities, as well as human activities such as plowing). As a result, the city’s albedo is reduced, amplifying the heating impact. Rural regions with higher wind speeds, especially in the winter, might also be colder than urban places.

Prediction

The UHI can be measured directly if a city or municipality has a good system for obtaining weather observations. An alternative is to use a complex simulation of the location to calculate the UHI, or to use an approximate empirical method. These models enable the UHI to be factored into projections of future temperature rises in cities as a result of climate change.

Impact on Animals

Heat tolerance is increased in ant colonies in urban heat islands at no expense to cold tolerance. 

Species that are good at colonising can take advantage of the conditions given by urban heat islands to thrive in areas where they are not normally found. The grey-headed flying fox (Pteropus poliocephalus) and the common house gecko are two examples (Hemidactylus frenatus). Following a rise in temperature in Melbourne, Australia, grey-headed flying foxes entered urban environments. Increased temperatures, which resulted in warmer winter conditions, made the city’s climate more similar to the species’ more northerly wilderness home.

Urban Cold Island 

At night, the same metropolitan region that is hot during the day can be cooler than adjacent rural areas, giving rise to the name “urban cold island.” Snow, for example, insulates plants in remote locations. When researching plant responses to urban surroundings, this was an unexpected finding.  The early morning urban cold island effect occurs because buildings within cities obstruct the sun’s solar radiation as well as the wind speed within the city.

Mitigation

The temperature difference between urban areas and the surrounding suburban or rural areas can be as much as 5 °C (9.0 °F). Nearly 40 percent of that increase is due to the prevalence of dark roofs, with the remainder coming from dark-colored pavement and the declining presence of vegetation. The heat island effect can be counteracted slightly by using white or reflective materials to build houses, roofs, pavements, and roads, thus increasing the overall albedo of the city.

Health Effect

UHIs have the ability to have a direct impact on urban dwellers’ health and well-being. Each year, an average of 1,000 individuals die in the United States due to excessive heat. Because UHIs are associated with higher temperatures, they have the potential to amplify and prolong heat waves within cities. The death rate during a heat wave grows exponentially with the maximum temperature, according to research, an impact compounded by the UHI

Conclusion

A city is an urban area. A rural place is located in the middle of nowhere. Heat and light from the sun reach both the city and the countryside in the same way. The ability of the surfaces in each environment to absorb and hold heat determines the temperature differential between urban and less-developed rural locations. If you go to a rural place, you’ll probably find that plants cover the majority of the land. As far as the eye can see, there is nothing but grass, trees, and farms covered in crops.Plants use their roots to absorb water from the ground. The water is then stored in their stems and leaves. Water ultimately finds its way to little holes on the underside of the leaves. The liquid water condenses there and is discharged into the atmosphere as water vapour. This is referred to as transpiration. It cools the environment naturally.