Journal of Environmental Protection, 2011, 2, 465-472
doi:10.4236/jep.2011.24054 Published Online June 2011 (http://www.SciRP.org/journal/jep)
465
Urban Heat Island Effect over National Capital
Region of India: A Study using the Temperature
Trends
Manju Mohan1, Anurag Kandya1, Arunachalam Battiprolu2
1Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, India; 2Wapcos (I) Ltd., Institutional Area, Sector-18, Gur-
gaon, Haryana.
Received October 11th, 2010; revised February 19th, 2011; accepted April 7th, 2011.
ABSTRACT
The local temperature is one of the major climatic elements to record the changes in the atmospheric environment
brought about by industrialization, increasing population and massive urbanization. The present study deals with the
annual and seasonal temperature trends and anomalies for maximum, minimum and mean temperatures of the four
meteorological stations of the Natio nal Cap ital Region (NCR) of India namely Safdarjung, Palam, Gurgaon and Roht ak
for the past few decades and their asso ciation with the developmen t through urbanization pro cesses. The annual mean
maximum temperature did not show any specific trend; however a consistent increasing trend was seen in the annual
mean minimum temperatures indicating an overall warming trend over the NCR especially after 1990. This warming
trend is contrary to the cooling trend observed by earlier studies till 1980’s in various other cities of India including
Delhi. However, the temperature trends in annual mean minimum temperatures reported in various countries (USA,
Turkey, Italy, etc.) across the world showed warming trends to be associated to the urbanization process of the cities
also. The current warming trends in temperature in the NCR Delhi based on the annual mean minimum temperatures
have thus been supported by the trends in other parts of the world and could b e utilized to infer the development proc-
ess in this region. The urbanization pattern within Delhi is reflected by the trends of differences in annual mean mini-
mum temperature of the two stations within the city namely Safdarjung and Palam. The significance of the warming
trends of the annual minimum temperature for the urban heat island effect is also discussed.
Keywords: Urban Heat Island, Temperature Trends, Urbanization, National Capital Region Delhi
1. Introduction
Urban Heat Island (UHI) is considered as one of the ma-
jor problems in the 21st century posed to human beings as
a result of industrialization and urbanization [1]. No
doubt, industrialization and urbanization improves our
material lives and comfort; however, many problems are
induced by these processes such as urban heat islands,
global warming, air pollution, etc. Significant research
efforts have been undertaken to evaluate the impact of
UHI on the urban environment in different parts of the
world [2-5]. The deterioration of the living environment,
increase in the cooling energy requirements [6], elevation
in the ground level ozone [7] and even an increase in the
mortality rates [8] are some of the few ill effects of urban
heat islands. The mass scale deforestation, the reduction
in the green cover, the increase in the built-up land, the
use of materials like concrete, asphalt, tar, etc. have sig-
nificantly altered the energy balance of the urban area
often causing the temperature to reach relatively higher
value than its surroundings. It is also believed that air
pollutants, in particular aerosols, can absorb and re- radi-
ate long wave radiation and inhibit the corresponding
radiative surface cooling producing a pseudo-green
house effect that may contribute towards the urban heat
island effect [1]. Kadioglu [9] studied the surface air
temperature trends in Turkey and concluded that night
time temperatures have a comparatively significant in-
crease while day time temperatures remain unchanged
over the study area. Cayan and Douglas [10] studied the
urban influences on surface temperatures in the South -
Western United States for the period 1930-1980 and
concluded that urban warming appears to be predomi-
nantly a night time phenomenon, with minimum tem-

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends 466
peratures displaying considerably more increase than the
maximum temperature. In another study, Thomas [11]
showed the urbanization effect based on climate record
for the period 1901-1984 across United States from the
analysis of mean seasonal and annual temperature time
series. The results indicated that annual mean tempera-
ture due to urbanization accounts for a warm bias of
about 0.06˚C in the US for this period. Another study
based on the mean annual surface air temperatures in
Rome during 1782 to 1975, found that the increasing
trend in urban temperatures was more conspicuous in the
minimum temperatures rather than in the maximum
temperatures [12,13].
Megacity Delhi, capital city of India located in the
northern part of the country (with semi-arid climatic
conditions) has experienced a rapid urbanization, espe-
cially in the past two decades i.e. 1990-2010. Tempera-
ture trends are studied earlier till 1986 [14,15] in Delhi
where a cooling trend was shown here in contrast to the
other cities such as Kolkatta, Mumbai and Bengaluru.
Focus on this city for the study arises due to its unex-
pected cooling trend and high pollution levels, significant
vehicular traffic (number of vehicles in the Delhi being
about sum total of vehicles put together of other three
megacities in India namely Mumbai, Chennai and Kol-
kata), highest population growth amongst all mega cities
etc [16]. Rupa kumar and Hingane [14,15] carried out the
long term variations of surface air temperature at major
industrial cities of India (Kolkata, Mumbai, Chennai,
Bengaluru, Pune and Delhi) using data for the past 86 to
112 years up to 1986. The mean annual temperature of
Delhi showed an overall decreasing tendency, with a
relatively warmer period during 1940-1960. Sahai [17]
carried out a case study for Nagpur, a centrally located
city in India to understand the cooling or cessation of
warming. Data from 1901-1992 was used for the subur-
ban site and from 1950-1992 for the urban site at Nagpur
city. This study on the diurnal asymmetry in maximum
and minimum temperature indicated that the role of sus-
pended particulate matter dominated that over green-
house gases. Gadgil and Dhorde [18] investigated the
annual and seasonal temperature trends over Pune using
temperature data of 100 years during the period
1901-2000. They reported a significant decrease in the
mean maximum temperature which was more predomi-
nant during the winter season. This study also empha-
sized the significant role of the suspended particulate
matter (SPM) in the ambient air for the cooling trend.
Many other studies [19-25] have been made on the ef-
fects of urbanization and industrialization on the local
climate, which generally indicate that the industrial cities
get more precipitation and that they are smoggier,
warmer and dirtier than the countryside [14]. Thus, local
temperature is one of the major climatic elements to re-
flect the changes in the atmospheric environment brought
about by industrialization, increasing population and
massive urbanization.
The present study deals with temperature trends of
annual mean maximum and minimum, annual mean, sea-
sonal mean maximum and minimum temperatures; as
well as temperature anomalies at different time periods
during 1906-2005 in the National Capital Region (NCR)
of India. In NCR, the temperature data was available at
four sampling stations namely; Rohtak, Gurgaon, Palam
and Safdarjung established by the India Meteorological
Department. Seasonal and annual temperature trends and
anomalies are studied for mean, minimum and maximum
temperatures and their association to Urban Heat Island
is discussed. There has been accelerated growth of the
National Capital Region in past few decades especially
since 1990 and there is no systematic study undertaken
that could highlight the impact of this rapid development
on the atmospheric environment. With this background,
the present study is undertaken for an in-depth analysis
of the changes in atmospheric environment brought about
by the rapid urbanization and industrialization in Na-
tional Capital Region through long term time series of
temperature data (40-100 years).
2. Materials and Methods
2.1. Study Area
The study area for the present study is National Capital
Region (NCR) of India as shown in Figure 1 which is
spread over an area of 33,578 sq. km. including National
Capital Territory of Delhi, and neighboring states of
Figure 1. Map of national capital region of India [26].

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends467
Haryana, Rajasthan and Uttar Pradesh (UP). The popula-
tion of NCR, as per 2001 census, was 11.5 million with
an average decadal rate of growth of about 29 % in the
last three decades. UP accounts for 31.2% of the total
NCR population while National Capital Territory, Delhi
contributes 37.2%, Haryana contributes 23.5% and Ra-
jasthan contributes 8.1%, as per 2001 census. A brief
description of the stations in study area is given here.
Gurgaon is the sixth largest city in the Indian state of
Haryana. According to the 2001 India census, Gurgaon
has a population of about 172,955. Gurgaon has grown
extensively during the last decade due to its proximity to
West Delhi and South Delhi and its emergence as a ma-
jor outsourcing destination and as a real estate market in
northern India. Rohtak district is located in southeastern
part of Haryana State and constitutes a major part of
eastern Haryana plain. Due to proximity to National
capital, the developmental activities are taking place very
rapidly. The district has witnessed rapid industrialization,
urbanization, diversification in agriculture and change in
occupation structure. Palam is a bustling residential area
located about 18 km south-west of Connaught Place, in
South West Delhi District. Dwarka - Asia’s largest resi-
dential colony is located next to Palam. Indira Gandhi
International Airport is located at Palam. Safdarjung is
also a residential area. Colonies are primarily residential,
and are bases for the affluent upper class. Safdarjung
airport, formerly Delhi’s main airport and now used for
trainees and small flights, is also located in this area.
The climate of NCR is mainly influenced by its inland
position and the prevalence of continental air during a
major part of the year and has extreme climatic conditions.
Delhi has three distinct seasons namely; summer, mon-
soon and winter. The summer season (March, April, May
and June) is governed by high temperature and hot, high
speed winds. The monsoon (July, August and first half of
September) is dominated by rains and high humidity lev-
els in air. The winter season starts in late November and
ends with the month of early February. This period is do-
minated by cold, dry air and ground-based inversion with
low wind conditions. The months of February and March
are also referred to as spring period and the months of
October and November constitutes postmonsoon season.
2.2. Data
Historical data in NCR for four meteorological stations
(one each at Rohtak, Gurgaon, Palam and Safdarjung)
was made available by Indian Meteorological Depart-
ment (IMD). For Safdarjung station, monthly average
data (both maximum and minimum) was available form
1906-2005, for Gurgoan it was from 1968-1999 while for
the remaining two stations i.e. Rohtak and Palam it was
from 1968-2005. The extent of the data availability was
nearly 100% for both Safdarjung and Palam while it was
86% for Rohtak and 82% for Gurgoan. The meteoro-
logical stations were at the same place throughout the
mentioned time period respectively.
2.3. Methodology for Trend Analysis
Seasonal and annual temperature trends and anomalies
are studied for mean, minimum and maximum tempera-
tures. For seasonal analysis, the monthly data was further
averaged with respect to the season. For trend analysis,
polynomial trend line of order 5 was used that is selected
based on trial and error method for various orders of
polynomial fitting and the resulting correlation coeffi-
cients. Temperature anomaly was calculated by the for-
mula Δt = T0 - Tavg where Δt is the temperature anomaly,
T0 is the annual average temperature (either maximum or
minimum as the case may be) and Tavg is the overall av-
erage of the temperature for the study period for maxi-
mum or minimum. Mean temperature is based on the
average of the mean minimum and mean maximum tem-
peratures. Significance test at 95% confidence level was
performed to assess the usability of the trends in data.
3. Results and Discussion
It is concluded from various studies discussed in section
1 of this paper that urban warming appears to be pre-
dominantly a night time phenomenon, with minimum
temperatures displaying considerably more increase than
the maximum temperature. Further, it was shown that
increasing trend in urban temperatures was more con-
spicuous in the minimum temperatures rather than in the
maximum temperatures [13].
It is noted from the significance test (at 95% confi-
dence level) that there is presence of trend in minimum
temperatures while no specific trend in the maximum and
mean temperatures exist. The significance test showed
autocorrelation coefficients between 0.524 to 0.738 for
the minimum temperatures for the four stations while
that for maximum temperatures and mean temperatures
these values are low and ranged from 0.011 to 0.254 and
0.054 to 0.398 respectively. Therefore further discussion
considers all trends based mostly on minimum tempera-
tures. Furthermore, due to the availability of complete
data as long time series of two stations within Delhi i.e.
Safdarjung and Palam, the temperature anomalies amongst
these stations has also been studied and detailed infer-
ences are discussed separately. Seasonal and annual
analysis of the temperature trends based on the data de-
scribed in section 2.2 is discussed below:
3.1. Temperature Trends at the Four
Meteorological Stations of NCR
The following text describes the temperature trends and

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends 468
anomalies based on annual mean minimum temperatures
and that of the four seasons respectively in National
Capital Region at Safdarjung, Palam, Gurgaon and
Rohtak. The trends are depicted through figures as well.
Figure 2(a) and Figure 2(b) describe the annual mean
minimum temperatures along with the trend line (as
shown by the dotted line in the figure) at Safdarjung and
Palam respectively while Figures 3, 4, 5 and 6 describe
the annual and seasonal mean minimum temperature
along with the trend line at Safdarjung, Palam, Gurgaon
and Rohtak respectively. The annual and seasonal trends
at each of these stations are discussed below:
1) Safdarjung:
 The annual mean minimum temperature trend indi-
cates, in general, a warming trend since 1950 barring
few years in mid eighties.
 In general summer and winter seasons show a warm-
ing trend except few years in summer season in early
eighties and in late nineties during winter season.
 A consistent warming trend was observed while ana-
lyzing the seasonal mean minimum temperature for
the monsoon season during 1968-2005.
 A warming trend was observed for the seasonal mean
minimum temperature for the post-monsoon season
after 1992 barring past few years.
 Out of the four stations covered in the present study,
Annual Mean Minimum Temperature at Safdarjung
1906-2005
17.00
18.00
19.00
20.00
21.00
1906 1911 1916 1921 1926 1931 1936 1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001
Years
Temperature (deg C
)
Safdarjung Poly. (Safdarjung)
years
Temperature (deg C)
(a)
Annual Mean Minimum Temperature at Palam 1968-2005
16.0
17.0
18.0
19.0
20.0
1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Years
Temp e ratu re (d eg C)
Palam Poly. (Palam)
years
Temperature (deg C)
(b)
Figure 2. (a). Annual mean minimum temperature at saf-
darjung during 1906 - 2005; (b) Annual mean minimum
temperature at palam during 1968 - 2005.
Annual and Seas onal Minimum T emperature Vari at ions a t
Safdarjung (1968 - 2005)
5.00
10.00
15.00
20.00
25.00
30.00
1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Y
Temperature (deg C
)
Winter Summer Monsoon Post MonsoonAnnual Average
Temperature (deg C)
years
Figure 3. Annual and Seasonal Mean Minimum Tempera-
tures at Safdarjung during 1968 - 2005
Annual and Seasonal Minimum Tem
p
erature Variations at
Palam (1968 - 2005)
5.00
10.00
15.00
20.00
25.00
30.00
1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Year s
Temperature (deg C
)
Winter Summer Monsoon Post MonsoonAnnual Average
years
Temperature (deg C)
Figure 4. Annual and Seasonal Mean Minimum Tempera-
tures at Palam during 1968 - 2005.

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends469
Annua l
and
Seasonal
Minimum
Temperature
Variations
at
Gurgoan (1968 - 1999)
4.00
9.00
14.00
19.00
24.00
29.00
1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998
Year s
Tem perature ( deg C
)
Winter SummerMonsoon Post MonsoonAnnual Average
years
Temperature (deg C)
Annual and Seasonal Minimum Temperature Variations at
Gurgaon (1968-1999)
Figure 5. Annual and Seasonal Mean Minimum Tempera-
tures at Gurgaon during 1968 - 1999.
p
Rohtak (1968 - 2005)
0.00
5.00
10.00
15.00
20.00
25.00
30.00
1968 1971 1974 1977 1980 1983 1986 1989 1992 1995 1998 2001 2004
Years
Temperature (deg C
)
Winter Summer MonsoonPost MonsoonAnnual Average
years
Temperature (deg C)
Annual and Seasonal Minimum Temperature Variations at
Rohtak (1968-2005)
Figure 6. Annual and Seasonal Mean Minimum Tempera-
tures at Rohtak during 1968 - 2005.
earlier work of Rupa Kumar and Hingane [14] in-
cluded only Safdarjung station till the year 1986 and
only mean temperatures were considered. The present
study confirms the findings of the previous study that
Delhi showed an overall cooling tendency till mid
eighties, with a relatively warmer period during
1940-1960, as evident by the annual mean tempera-
ture variation. However, based on the annual mean
minimum temperature variations, the present study
brings to light the fact that there is a significant
warming trend in Delhi observed after 1990 which
can be linked to the rapid growth of the city in this
period in terms of population, transportation and in-
frastructure development.
2) Palam:
 The annual mean minimum temperature analysis in-
dicates a warming trend till 1996 and thereafter a
marginal cooling trend.
 The seasonal mean minimum temperatures for win-
ters indicate a warming trend except 1994-2002.
 The seasonal mean minimum temperatures for sum-
mers indicate a consistent warming trend throughout.
 There was a consistent warming trend observed for
the seasonal mean minimum temperature for mon-
soon season as well.
 The seasonal mean minimum temperature for
post-monsoon indicates a warming trend till 1998 fol-
lowed by a cooling trend.
3) Gurgoan:
 The annual mean minimum temperature shows a con-
sistent warming trend after 1980.
 There is an overall warming trend prevalent in the
seasonal mean minimum temperatures for all the four
seasons.
4) Rohtak:
 The annual mean minimum temperature shows a
warming trend except during 1988-1991.
 The seasonal mean minimum temperatures for sum-
mers indicate a warming trend after 1982, while that
for winters it was after 1999.
 Considering missing data, monsoon season shows a
warming trend 1989 onwards while post-monsoon
shows a marginal cooling trend.
3.2. Inter Comparison of the Temperatures of
the Two Stations within Delhi:
An inter comparison of the temperature trends of the two
stations within Delhi i.e. Safdarjung (28.58 N, 77.20 E)
and Palam (28.57 N, 77.12 E) is also performed to un-
derstand the impact of urbanization on temperature. The
annual mean maximum temperature difference between
Safdarjung and Palam stations is shown in Figure 7(a).
Based on the annual mean maximum temperature it can

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends 470
be inferred that Palam is relatively warmer than Safdar-
jung throughout the study period. As pointed out in this
study and reported by others that annual mean maximum
temperature trend is not affected by the urbanization pat-
terns to a great extent. Figure 7(b) shows the annual
mean minimum temperature difference between the two
stations. It is interesting to observe the annual mean
minimum temperature differences between Safdarjung
and Palam which clearly projects the impact of urbaniza-
tion on night time temperature. During the 1968-1985, it
was Safdarjung which had higher night time tempera-
tures, however, during 1986-1999, it was generally
Palam which had the higher night time temperatures.
After 2000, the two stations had almost the same annual
mean minimum temperatures as Palam had also urban-
ized as most of the other areas in the city. The major ur-
banization in Palam area stated after 1986 with the com-
ing up of Asia’s largest residential colony namely;
Dwarka, a major new international terminal at the Palam
Airport which was renamed as Indira Gandhi Interna-
tional (IGI) Airport, etc.
3.3. Temperature Trends across NCR
From the above inferences it can be concluded that the
annual mean maximum temperature did not show any
specific trend however the annual mean minimum tem-
perature indicates a warming trend in general over the
National Capital Region. The present study confirms the
findings of the previous study that Delhi showed an
overall cooling tendency, with a relatively warmer period
(a)
(b)
Figure 7. (a) Annual Mean Maximum Temperature differ-
ence between Safdarjung and Palam during 1968 - 2005; (b)
Annual Mean Minimum Temperature difference between
Safdarjung and Palam during 1968 - 2005.
during 1940-1960. However, based on the annual mean
minimum temperature variations, the present study brings
to light the fact that there is a significant warming which
has happened after 1990. The study infers a warming
trend at Safdarjung after 1990, while an overall warming
trend at all the other three stations. The inter comparison
of the two stations within Delhi also showed the impact
of urbanization on the annual mean minimum tempera-
ture. A warming trend based on the annual mean mini-
mum temperature in different countries across the world
has been reported by various authors. Kadioglu [9] con-
cluded that night time temperatures have a comparatively
significant increase while day time temperatures remain
unchanged over Turkey. Cayan and Douglas [10] have
also concluded that urban warming appears to be pre-
dominantly a night time phenomenon, with minimum
temperatures displaying considerably more increase than
the maximum temperature in the south western United
States during recent decades. Colacino and Rovelli [12]
based on the analysis of mean annual surface air tem-
peratures in Rome during 1782 to 1975 showed that the
increasing trend in urban temperatures was more con-
spicuous in the minimum temperatures rather than in the
maximum temperatures.
The causes for the increase in the night temperatures
and also the urban heat island effect are very complicated,
but include the energy stored by the denser urban surface,
decreased evapotranspiration in cities and anthropogenic
heat generation [11]. At various periods during a city’s
growth and development, any of these could be the major
cause for the increase in the temperatures of the urban
city centers or the so called Urban Heat Island (UHI)
intensity. Moreover, it is known that night temperatures
get warmer due to the very high levels of energy con-
sumption and significant amount of waste heat stored in
the walls of buildings, streets, etc.; which gets released
during the night. Rupa Kumar and Hingane [14] showed
cooling trends in annual mean temperatures in Indian
cities including Delhi in eighties while the trends in the
present study (post eighties or nineties) for annual mean
minimum temperature shows mostly the warming. Thus
annual mean minimum temperature trends in NCR Delhi
seem to show synchronization with the pace of develop-
ment in this region.
4. Conclusions
The present study of the temperature trends (annual and
seasonal) and temperature anomalies, both based on an-
nual mean maximum and minimum temperatures in Na-
tional Capital Region at Safdarjung, Palam, Gurgaon and
Rohtak lead to the following conclusions:
 There is a warming trend experienced in general over
the National Capital Region in past few decades.

Urban Heat Island Effect over National Capital Region of India: A Study using the Temperature Trends471
 The annual mean maximum temperature did not show
any specific trend however the annual mean mini-
mum temperature indicates a warming trend in gen-
eral over the National Capital Region indicating sig-
nificant urbanization process in past few decades.
 The inter comparison of the annual mean minimum
temperatures of two stations within Delhi (Safdarjung
and Palam) infers that the night time temperatures
trends have synchronized well with the pace of ur-
banization in the city.
 Except post-monsoon season, there is generally an
increasing trend in annual mean minimum tempera-
ture at all the stations and seasons.
 Annual mean minimum temperature time series can
provide useful information on the changing develop-
ment scenarios in a region and may indicate the likely
impact on the urban heat island effect especially
where time series of elaborate field campaigns are not
available.
 Increasing warming trends in the night-time tempera-
tures reflect the contribution of changing land-use
patterns and additional anthropogenic heat that may
enhance the urban heat island intensities in the city.
 Warming trends in temperature reflects local warming
and future studies are required to study it’s Impact on
global warming.
5. Acknowledgements
The authors acknowledge Indian Meteorological De-
partment for providing the necessary temperature data of
the four meteorological stations of the National Capital
Region. The financial support extended by Indian Space
Research Organization (ISRO) through their RESPOND
programme for carrying out this study is also gratefully
acknowledged. The help extended by Shweta Bhati, Re-
search Scholar at Centre for Atmospheric Sciences of IIT
Delhi is also duly acknowledged.
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