Urban Heat Island (UHI) Effect
The growing urbanisation in India has caused rapid changes in land use and land cover within urban areas. These rapid changes have brought a change in the microclimatic conditions particularly with respect to its thermal structure. The phenomenon of increased higher temperatures within city compared to the surrounding rural areas is known as the ‘Urban Heat Island’ (UHI).
Causes and consequences of UHI
The causes for urban heat island are several. Dense high-rise buildings constructed in urban areas provide multiple surfaces for reflection and high absorption of solar radiation. Urban structures are covered with materials such as concrete and asphalt that have low albedo value causing absorption of more heat. The reduced vegetative cover in urban areas reduces the natural cooling affect from evapotranspiration mechanism. Air pollution form vehicles and industrial activities has an indirect relationship with increasing temperatures in urban areas. Air-conditioning systems and manufacturing activities further discharge heat in to environment. Geographical location of city such as proximity to water bodies and hills play crucial role in formation of urban heat island.
The presence of urban heat island poses threats to human life, animals, plants, regional and global climate patterns. The high temperatures may lead to heat stress deaths and morbidity problems. Plants growth can be effected. It leads to high energy consumption to avoid thermal discomfort, more greenhouse gas emissions, increased air pollution, anomalies in rain pattern etc.
Planting trees and increasing vegetation is the simple way to reduce urban heat island effects. Trees substantially reduce the temperatures by increasing the albedo of the surfaces. Planting more trees directly and indirectly reduces CO2 from the atmosphere. Trees directly reduce CO2 from atmosphere as they use carbon during photosynthesis. Trees indirectly reduce CO2 from atmosphere because their cooling effect reduces burden on power generation. Green roofs and cool roofs having high albedo value surfaces also reduce urban heat island effect.
