The phenomenon of global warming remains more pronounced in the urban areas, for the reason cities house large concentration of people and activities in a small/compact urban space.Densely-built downtown areas tend to be warmer than suburban residential areas or rural areas.. UHI not only raises urban temperatures but also increases ozone concentrations because ozone is a greenhouse gas whose formation will accelerate with the temperature. Tokyo, an example of an urban heat island. Normal temperatures of Tokyo go up higher than those of the surrounding area. However, it needs to be understood and appreciated that climate change is not the cause of urban heat islands but it is causing more frequent and more intense heat waves which in turn amplify the urban heat island effect in cities. Major reasons for ever growing global warming and climate change can be attributed to the; Nature and natural; Human-Driven; population; Rapid Urbanisation; Irrational Urban planning; High Density; Inefficient Transportation ;Large generation/consumption of fossil fuel based Energy; Unsustainable Buildings; Polluting Industry & Manufacturing; Unsustainable Agriculture; Irrational Development; Large scale Deforestation; Lack of open spaces and individual life-choices;

1. Factors Causing Urban Heat Island ;
*Jit Kumar Gupta
** jit.kumar1944@gmail.com
The term heat island refers to any area that becomes relatively hotter than the
surrounding, largely due to natural reasons, human interventions and human-led
activities. Over the course of Earth’s existence, volcanic eruptions, fluctuations in solar
radiation, tectonic shifts, and even small changes in our orbit have all impacted and
transformed planetary warming and cooling patterns. Further, all human acts of growth
and development remain anti-thesis to nature , natural resources and climate.
Accordingly, human-led development remains largely responsible for adversely impacting
and causing numerous changes in prevailing climatic conditions of any place and region.
Changes happening in climate invariably distorts the existing balance and create adverse
climatic conditions. Climate change , basically and essentially has been recognized to
be the outcome of the ever increasing global average temperature which is known to
adversely impact the climate system of planet earth besides making long-term changes
which have shaped the earth's climate. However, adverse impact of climate change have
become more pronounced in the recent times, due to large increase in human population,
rapid shift in population from rural to urban settlements, rapid and massive
industrialization, massive mechanized fossil fuel based transportation; burning of fossil
fuels for generating energy, large scale deforestation for sourcing land for human
habitation and undertaking agriculture ; besides promoting energy intensive agricultural
and industrial practices. In addition, natural processes, like El Niño, La Niña, volcanic
activity, changes in the Sun’s energy output, variations in earth’s orbit besides human
activities, are also known to contribute to climate change. Urban activities have been
evaluated as a major sources of greenhouse gas emissions. Compact, dense urban
development invariably increases the urban heat island effect, leading to higher
temperatures and increased exposure. Cumulative impact of all these human and natural
activities, have been massive addition to greenhouse gases involving carbon
dioxide and methane. Greenhouse gases are known to absorb some of the heat that
earth radiates after it gets heat radiation from sunlight. Larger amounts of these
gases trap more heat in earth's lower atmosphere, causing global warming.
The main cause of the UHI effect is from the modification of land surfaces while waste
heat generated by energy usage remains the secondary contributor.Studies have

2. revealed that urban areas are known to record higher temperature when compared to
rural hinterland and rural settlements. The temperature difference is usually larger at night
than during the day, and is most apparent when winds are weak, under block conditions,
particularly during the summer and winter. The difference in temperature recorded
between an inner city and its surrounding suburbs in USA is frequently mentioned in
weather reports, as in "68 °F (20 °C) downtown, 64 °F (18 °C) in the suburbs. In the
United States, the difference during the day is between 0.6–3.9 °C (1–7 °F), while the
difference during the night is 1.1–2.8 °C (2–5 °F). Besides impacting temperature, UHI is
also known to decreases air quality by increasing the production of pollutants such
as ozone, and decreases water quality as warmer waters flow into area streams and put
stress on their ecosystems.
 The phenomenon of global warming remains more pronounced in the urban
areas, for the reason cities house large concentration of people and activities in
a small/compact urban space.Densely-built downtown areas tend to be warmer
than suburban residential areas or rural areas.. UHI not only raises urban
temperatures but also increases ozone concentrations because ozone is
a greenhouse gas whose formation will accelerate with the temperature. Tokyo,
an example of an urban heat island. Normal temperatures of Tokyo go up higher
than those of the surrounding area. However, it needs to be understood and
appreciated that climate change is not the cause of urban heat islands but it is
causing more frequent and more intense heat waves which in turn amplify the
urban heat island effect in cities. Major reasons for ever growing global warming
and climate change can be attributed to the; Nature and natural; Human-Driven;
population; Rapid Urbanisation; Irrational Urban planning; High Density;
Inefficient Transportation ;Large generation/consumption of fossil fuel based
Energy; Unsustainable Buildings; Polluting Industry & Manufacturing;

3. Unsustainable Agriculture; Irrational Development; Large scale Deforestation;
Lack of open spaces and individual life-choices; as briefed below;
Urbanization; Urbanization, as a process, has been recognized as the prime
reason for ushering in an era of climate change and global warming. Urbanization
has been responsible for changing the physical, social, economic , environmental
structure, fabric, growth and development trajectory of human settlements backed
by concentration of activities, mechanization of system of production, large scale
migration, production and use of large fossil fuel based energy and massive
addition to built environment besides changing footprints and typologies of
buildings and altering and increasing mechanized mobility . All this led to
creating urban heat island (UHI) effect, as a distinct feature of urban growth, urban
development and urabanisation; making urban areas warmer than
surrounding rural areas.The urban heat island temperature difference is not only
usually larger at night than during the day, but also larger in winter than in summer.
 Industrialization; Having roots in the invention of steam and fossil fuel based
energy has been one of the major reasons for making urban areas hotter when
compared with the surrounding rural hinterland. Burning of coal and generating
large volume of CO2, Methane and other effluents has led to not only adding
enormous heat in the environment besides trapping heat close to the earth, raising
the local temperatures. Cumulative effect of industrialization has been to change
the local climate and heating the urban settlements.
 Population; Population at any place remains the major determinant of urban heat
island. As population grows, human settlements for housing increased population,
tends to expand its area leading to increase in average temperature. High density
neighborhoods, as already stated, invariably are found to be hotter than low
density development.
 Density; Urban growth is invariably marked by the large concentration of people,
vehicles, housing etc. in a limited area, giving rise to higher order of density and
intensity of development. Density and urban heat island remain positively related.
Higher the density / intensity of growth and development in any city; higher will be
the temperature of a place. Even within the city, different neighborhoods are
known to record different temperatures. Neighborhood housing high income
groups, having low housing/population density, are less impacted by the heat
island when compared with neighborhoods having high density/low income
housing.
 Open Spaces; Dense urban living, without green spaces lead to a creating
pronounced urban heat island effect Studies made have revealed that open
spaces and heat island remain negatively/ inversely connected. Large proportion
of green spaces with large number of trees, invariably lead to lower temperature
because of the capacity of trees to cool the air by trans-evaporation , provide

4. shadow to the urban spaces and reduce the intensity of solar radiation on the land
surface. Heat can be reduced by tree cover and green space, which act as sources
of shade and promote evaporative cooling.
 Built Environment; Along with population, urban growth is marked by large scale
construction of buildings and other structures necessary to accommodate growing
populations. These surfaces absorb, rather than reflect the sun's heat, causing
surface temperatures and overall ambient temperatures to rise .In addition,
buildings remain large consumers of energy and resources besides generators of
large waste, Buildings are known to have energy implications in terms of embodied
energy and operation and maintenanace energy because energy is used both
during the construction for the production of materials and services used in the
construction of buildings. In addition, buildings continue to consume energy during
its entire life cycle for heating, cooling, ventilation and lighting besides running
large number of energy based appliances used within the building. Buildings,
unless planned, designed and constructed as energy-efficient and sustainable
buildings, are known to have major implications in terms of higher consumption of
energy and resources. Ignoring orientation, cross ventilation, climate and natural
lighting in building design, invariably increases the inside temperature of building,
necessitating the need of air-conditioning, leading to consumption of higher
energy , promoting urban temperature, creating heat island and propelling climate
change. . Tall buildings within urban areas provide multiple surfaces for the
reflection and absorption of sunlight, which by “urban canyon effect" increases the
efficiency with which urban areas are heated. Tall and cluster of buildings also
block the flow of wind, which inhibits cooling by convection and prevents pollutants
from dissipating. Existence of inverse interactions between heat and built
infrastructure is known to increase the risk of causing enormous heat stress
among urban residents.
 Urban Planning; Unfortunately, role , relevance and importance of urban
planning, in making cities warm and promoting climate change, has neither been
understood nor appreciated, with the result cities are being planned, designed,
developed and managed without understanding the implications of urban planning
in making cities sustainable. Master Plans and Development Plans, prepared for
the rationalising, promoting the planned and sustainable development of cities,
don’t space the climate change as a factor in the said plans. In the process cities
go on increasing and expanding in length, breadth and contents, increasing
distances between place of work and residence/leisure/ healthcare /education/
services, increasing trip length, travel demand and inducting more mechanized
vehicles. In addition, urban planning negates the very concept of climate,
orientation, solar movement and vegetation at local level , leading to formation of
heat canyons at the local level, resulting in considerable increase in temperatures

5. at the local level ,making urban areas warmer. In fact, Master Plans/ Development
Plans have accelerated the process of climate change and global warming.
 Increasing Black Surfaces; Besides nature, large number of manmade factors
have been enumerated as promoter of higher temperature in urban areas. Large
scale metaling and paving of earth surfaces, by making roads, flyovers, footpaths,
pavements, parking lots and cycle tracks, have led to reduction in the earth surface
for absorbing the solar heat. In addition, large proportion of urban areas is covered
by the building footprints provided for shelter, offices, trade and commerce,
industries , leisure, healthcare, education etc. Majority of these surfaces are of
dark colours, because of the materials used in making them. Dark colours are
known for their character and capacity of absorbing and storing majority of solar
heat falling on them, instead of radiating. Accordingly, dark surfaces absorb
significantly more solar radiation, which causes urban concentrations of roads and
buildings to heat more than suburban and rural areas during the day; Increase in
vehicular population coupled with increase in population, have cumulatively led
to increasing the volume of such surfaces. Commutative impact of the dark
surfaces lead to raising the temperature of these surfaces and making cities warm
and hot, particularly during the summer season because surfaces in the urban
areas tend to warm faster than those of the surrounding rural areas. Considering
high heat capacities, urban surfaces act as a giant reservoir of heat energy.
Concrete can hold roughly 2,000 times as much heat as an equivalent volume of
air. As a result, the daytime surface temperature of hard surfaces becomes very
high . This warming of surfaces also has the effect of generating convective winds
within the urban areas. The urban heat island temperature difference is not only
usually larger at night than during the day, but also larger in winter than in summer.
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
 Deforestation; Large increase in population and addition to urban limits,
invariably leads to encroaching on the agricultural land and converting them for
meeting the needs of urban areas. Large number of trees and existing flora and
fauna, gets lost in the haze of urban development. Trees are known for their
capacity to modulate temperature by absorbing solar radiation, using solar energy
for making food and growth of trees beside shading the area under the canopy of
the tree. Loss of trees and green vegetation remains the major reason for
promoting the local temperature and climate change. Another major reason is the
lack of evapotranspiration caused by lack of vegetation in urban areas. The U.S.
Forest Service found in 2018 ; cities in the United States are losing 36 million trees
each year. With decreased amount of vegetation, cities also lose the shade and

6. evaporative cooling effect of trees. Heat islands also becomes a reality by
proximity to different types of land cover. Proximity to barren land causes urban
land to become hotter and proximity to vegetation makes it cooler
 Traffic & Transportation; Traffic and transportation remains the two worst gifts of
urabanisation, causing numerous problems of growth, development, environment
and ecology in urban areas. Increase in travel demand and ever increasing trip
length, caused by ever increasing travel distances between different land uses in
urban areas and induction of large increase in mechanized fossil fuel-based
vehicles to transport goods, services and human beings, have emerged as the
major cause of city getting warmer by the emission of the Co2 and other gasses.
Traffic and transportation invariably promote heat islands because movement of
vehicles requires vegetation to be replaced by asphalt and concrete for roads.
Pavements, parking lots, roads or, more generally speaking transport
infrastructure, contribute significantly to the urban heat island effect. For example,
pavement infrastructure is a main contributor to urban heat during summer
afternoons in Phoenix, United States. Vehicular traffic has been considered as
one of the major reasons that increase the severity of UHI especially in mega cities,
particularly in areas having high intensity of vehicular movement. Waste heat from
automobiles, air conditioning, industry, and other sources also contributes to the
UHI. High levels of pollution in urban areas can also increase the UHI, as many
forms of pollution change the radiative properties of the atmosphere
 Nature- led causes; Part of the problem pertaining to climate change can be
attributed to the natural phenomena, which created the planet earth and under
the shadow of which planet earth keeps its identity. . Over the period these
natural phenomenon and natural forces coupled with earth’s existence, volcanic
eruptions, fluctuations in solar radiation, tectonic shifts, and even small changes
in our orbit have all impacted planetary warming and cooling patterns to a large
extent. However, data sourced on heat from different sources, have show that
global warming Some amount of climate change can be attributed to natural
phenomena. Over the course of Earth’s existence, volcanic eruptions, fluctuations
in solar radiation, tectonic shifts, and even small changes in our orbit, have
considerable effects on planetary warming and cooling patterns. But climate
records are able to show that current global warming—particularly what has
occurred since the start of the industrial revolution—is happening quicker and
much faster than ever before. According to NASA, these natural causes are still
in play today, but their influence is too small or they occur too slowly to explain
the rapid warming seen in recent decades.” Records refute
the misinformation that natural causes are the main reasons behind climate
change. Fossil fuel; industry and built environment and transportation are the
major source contributing to rise in temperature.