Urban heat islands

Delhi 2050 Workshop, Delhi, 30 Jan – 3 Feb 2012

Assessment of Urban Heat Island Effect in
Megacity Delhi

Manju Mohan,
Professor
Centre for Atmospheric Sciences
Indian Institute of Technology, Delhi
India
mmohan6@hotmail.com
1

Urban Heat Island: Introduction
• The urban heat island effect is defined as any urban area which has a
tendency to be warmer than a surrounding rural/lesser developed
area.
• Some of the earliest incidences of urban heat island effect were
observed in late nineteenth century in cities such as London , Paris,
Berlin and other European cities which were major centers of
industrial activity.
• Today, the phenomenon of urban heat island is an existent issue of
concern in many cities of both developed and developing nations of
the world.

Prof. Manju Mohan, IIT Delhi 2 Delhi 2050 Workshop, 30 Jan – 3 Feb 2012

Classical representation of temperature profile of an urban area


Heat Island Effect: Causes
• Absorption of heat by urban infrastructure
– Urban areas are characterised by concrete surfaces, high rise
buildings and dense human as well as vehicular population.
– Man made structures such as roads absorb solar radiation during
the day resulting in increase of temperature of those surfaces and
the air in contact with them.
– As the day progresses, a dome of warm air forms over the urban
areas.
– After the sun sets, the buildings form a canopy structure
preventing the heat loss to the upper atmosphere. Thus
temperatures remain elevated, and so the heat island effect
persists during the night as well.


• Lack of vegetation surface
– Vegetated surfaces provide moisture for evaporation. Thus lack of
moisture restricts heat dissipation.



• Apart from changes in LULC, Anthropogenic Heat adds to the urban
heat island effect.

– Heat released by electrical equipments and air conditioners, and
heating systems
– heat released by vehicle exhaust


Urban Heat Island Effect in Delhi


Introduction

• Delhi, the capital city of India, has witnessed a consistent
decennial population growth at the rate of over 45 % for last six
decades.
• The corresponding urban infrastructure development is steadily
increasing the resource dependency and anthropogenic heat
emissions.
• Most of the studies on UHI in Delhi were conducted in 1980’s and
thus there exists a dearth of recent studies regarding urban
climatological assessment in Delhi.


Land Cover Changes in Delhi: 1997-2008*

Land Cover changes for different classes from 1997-2008 (Sq. km in Total area)

*Mohan et al, JEP, 2011

Prof. Manju Mohan, IIT Delhi Delhi 2050 Workshop, 30 Jan – 3 Feb 2012

Land Cover Changes in Delhi: 1997-2008*
• An overall net increase of 251.18 km2 (16.87 %) in built–up area has
been observed in last decade.

• On the other hand there is a decrease in agricultural area of 146.75
km2 by combining the decrease in crop and fallow land.
• There is another significant decrease in wasteland by 80.62 km2 by
combining scrub-land and sandy areas.

• Area covered by water bodies reduced from 58.26 km2 in 1997 to
27.43 km2 in 2008 which is about 52.9% decrease in a ten year period.



Land Cover Changes in Delhi: 1997-2008 contd..

• Thus increase in built-up area in the city has been on the expense of
majorly from the agricultural and waste land together with the
shrinking water bodies.

• As the city developed, the built-up category replaced most of the land
classes like sandy areas, fallow land and scrub land. The changes in LU-
LC classes are more from population pressure as the population
growth is very high in Delhi.


Temperature trends in Delhi*
• An increasing trend shows impact of urbanisation in form of increase
in built up area.
• increasing warming trends in the night-time temperatures reflect the
contribution of changing land-use patterns and additional
anthropogenic heat.


Temperature trends as proxy to urbanization
• The association of increasing temperatures with urbanization was
further strengthened by the trends of differences in annual mean
minimum temperature of the two stations within the city namely
Safdarjung and Palam.

Annual Mean Minimum
Temperature difference
between Safdarjung and
Palam during 1968 - 2005

• During the 1968-1985, it was Safdarjung which had higher night time
temperatures because it was more built up than Palam. After 2000,
the two stations had almost the same annual mean minimum
temperatures as in subsequent years Palam had also urbanized.


Delhi: Usual Climate Scenario

• Delhi is located at 28.61 °N and 77.23 °E at mean sea level of 216 m.

• With a population of 22.4 million and daily influx of about 665
people, the city and its surrounding areas form fourth largest urban
agglomeration in the world.

• Delhi has four distinct seasons namely:
- Summer (March, April, May and June),
- Monsoon (July, August and first half of September),
- Post Monsoon (October, November) and
- Winter (December-February).


Study Area Network of Delhi (contd..)
• The national capital territory of Delhi covering an area of 32 x 32 km
was chosen as the study area as shown in Figure
• The entire area is divided in 16 major grid cells of 8 x 8 km where at
least one ground level station was allocated.
• Some of the grids with different land-use type had more than one
station so as to get a representation of the terrains therein.
• The locations and LULC categories of these stations is depicted in
Figure 1.
• LULC categories used for location of measurement sites can broadly be
classified into Urban Built Up areas, Green Areas, Open Areas and
Riverside categories.


Layout of field measurement points their LULC category in the study area

Classified Image of Study Domain

Study Area Network of Delhi (contd..)

• In all, 30 sites (including 3 weather stations and 27 surface
micrometeorological stations) were chosen throughout the city so
as to represent a wide variety of land use/land cover categories.

• Temperature and humidity measuring instruments were installed
at the micrometeorological stations and weather stations were
installed at the rooftop and were equipped with instruments used
for recording wind speed and direction, dry bulb temperature,
relative humidity, atmospheric pressure and direct solar radiation.


Site Classification

Built Up Area
Green Cover Open Area Riverside

Dense Urban
Canopy Medium
Dense
Medium Dense Canopy-1 Forests
[MDUC I]
Medium Dense Canopy- 2
[MDUC II]

Less Dense Parks and
Canopy Gardens


BUILT UP AREAS
Dense Urban Canopy GREEN AREAS
•Sitaram Bazar (30)
Medium Dense Forests
•Bhikaji Cama (7)
Medium Dense Urban Canopy •Sanjay Van (24)
•Dwarka (6) : MDUC-I
Parks & Gardens
•Lajpat Nagar (9) : MDUC-I
•Hauz Khas Distt Park (28)
•Noida Sec-19 (10 )
•Buddha Jayanti Park (8)
• Janakpuri (12)-MDUC-I
•CP (14): MDUC-I
•Kaushambi(16): MDUC-I Micro- OPEN AREAS
•Rohini (17) :MDUC-I Meteorological
•Adarsh Nagar(19): MDUC-I •IIT (2)
•Civil Lines (20): MDUC-I Stations •Loni2 (23)
•Neb Sarai (4): MDUC-II •JNU
•Moti Nagar (13) : MDUC-II
•Vasant Kunj (24): MDUC-II
•Chirag Delhi (26) : MDUC-II RIVERSIDE AREAS
•Yusuf Sarai (29): MDUC-II
Less Dense Urban Canopy •Majnu Ka Tila (11)
•Gurgaon,Sec-23(1) •Sailing Club, Jamia Nagar (21)
•IIT (2)


Data Collection and Experiment Description

(Indo-Japanese Cooperative Study: IITD, IITR and Meisei University,
Japan)*

*Mohan et al, ICUC-7, Yokohama, Japan, 2009


Experiment Description
• Field experiments were carried out during 25-28 May 2008 and were named
as DELHI-I.
• The month of May is a typical summer month in Delhi.
• Temperature and humidity measuring instruments were fixed at all
micrometeorological stations. The instruments were installed at a height of
about 1.5 m from the ground level such that the ‘immediate’ surroundings of
the instrument were open and not obstructed by any tree or building.
• These instruments were set facing the South Direction to receive the solar
insolation for maximum duration of the day.
• In addition, 3 weather stations at the rooftop level (15m approximately)
measured wind speed and direction, dry bulb temperature, atmospheric
pressure, and global solar radiation.


Setting Up of Weather Stations

Calibration Phase

Calibration Set-Up of
Micrometeorological
Instruments


Weather Station installed at a roof


Setting Up of Micrometeorological Instrument at Site


Loni- Open Area

Sitaram Bazar- Dense Urban Canopy


Green Areas

Buddha Jayanti Park
Hauz Khas Distt Park
Natural Green Area
Natural + Cultivated Green Area
(Medium Dense Forest)

Sailing Club (River Bank)

Riverside Areas

Majnu Ka Tila (Near River Bank)

29

Weather Conditions during the Field Campaign

Parameter DELHI-I (25-28 May 2008)
Maximum Temperature 33.4 °C -37.2 °C
Minimum Temperature 19.6 °C -23.9 °C
Wind Speed 0-3.6 ms-1
Wind Direction WNW to SW
Rainfall Events 25 May, 26 May


Results: UHI Intensities in DELHI-I (May 2008)
• The dense commercial zone of Cannaught Place-Sitaram Bazar
observes higher temperatures on all experimental days.
• The heat island effect develops in the order of Cannaught Place-
Sitaram Bazar zone > Bhikaji Cama zone> Janakpuri Zone.
• The maximum UHI intensity of 8.3 °C was observed at Sitaram Bazar.
• All green areas (IIT-Hauz Khas-Sanjay Van and Buddha Jayanti Park)
fall under cooler pockets on all the days.
• Overall heat island intensity has been found to increase from 25th
May to 28th May.
• The riverside areas experience higher temperatures than green areas
but lower than those of urban canopies in vicinity.


32 32

30 30
22 22
28

19
23
Riverside 28

19
23

17 17
Areas
26 26
20 4 20 4
4
.2

24 21 24 21 3 .8

26 27
3 .6 3 .6
22 22 3 .4
3 .2 3 .2
13 13
M M
20 20 3
2 .8 2 .8
18 30 16 18 30 16 2 .6

12 14
2 .4
A A 12 14
2 .4
Y (k m )

Y (k m )
16 16 2 .2
8 2
8 2
14
1 .6 Y Y 14 1
1
.8
.6
12
6 12
6 1 .4

Dense
1 .2 1 .2
10 10
7 7
10 10 1
29 9 11 0 .8 29 9 11 0 .8
8 28
2
26
0 .4 Commercial 8 28
2
26
0
0
.6
.4
25
Areas 25
6 6 0 .2
24 27
0 24 27 0
4 T e m p e ra tu re 4 T e m p e ra tu re
1 4
( C) 1 4
( C)
2 2

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

32
X (k m )
UHI contours 32
X (k m )

30
22
23
(DELHI-I, 30
22
23
May 2008)
28 28

26 17 19 26 17 19
20 20
3:00 am
4 .6 5 .6
24 21 24 21 5 .2
4 .2
22 4 .8
22
3 .8
4 .4
13 13
20

18 30 16
3 .4

3
28 29 20

18 30 16
4
3 .6

12 14 M M 12
Y (k m )

14

Y (k m )
3 .2
16 2 .6 16
8 8
2 .8
14 2 .2

1 .8
A A 14 2 .4
2
6
Y
12
6
Y
12
1 .6
10 1 .4
10
10
7 10
7
29 9 11
Green
1 .2
1 29 9 11
8 28 8 28 0 .8
2 0 .6
2
26
Areas 26
0 .4
6 25 6 25
24 27 0 .2
24 27 0
4 T e m p e ra tu re 4 T e m p e ra tu re
1 4
( C)
1 ( C)
2 2
4

32
Prof. Manju Mohan, IIT Delhi
2 4 6 8 10 12 14 16
X (k m )
18 20 22 24 26 28 30 32
Delhi 2050 Workshop, 30 Jan – 3 Feb 2012
2 4 6 8 10 12 14 16
X (k m )
18 20 22 24 26 28 30 32

Summary Table of Maximum UHI (°C) in DELHI-I Experiments

Date Time 3:00 am 9:00 am 3:00 pm 9:00 pm
25 May 2008 - 4.6 6.3 2.8
26 May 2008 4.1 6.4 3.8 5.1
27 May 2008 4.2 5.1 7.6 4.2
28 May 2008 4.6 5.3 6.7 8.3
29 May 2008 5.6 - - -


The Indian Express, 25 September, 2009


The Hindustan Times,
26 September, 2009

36

Comparison with other international megacities

• Table 1 shows compilation of some reported UHIs in major cities of
the world based on various field observations.
• The average maximum daily UHI observed in DELHI-I measurements is
comparable to other cities like London, Beijing and Tokyo indicating
that urban heat island phenomenon in Delhi is of significant
importance as in other megacities of the world.
• With increasing urbanization, stronger heat island intensities are
expected to be observed here.


Table 1: UHI of some major megacites of the world
Heat Island Remarks
City Source
Intensity
Maximum: 5.4°C UHI in summer 2002
New York Gafﬁn et al (2008)
Mean: ~3°C
Maximum: 6°C Sarkar and Ridder 12 Day experiment in
Paris
Mean: 2.56°C (2011) June 2006
Maximum UHI in
London 8-9 °C GLA (2006) summer 2003 heat
wave episode
Wang and Hu Maximum UHI in July
Beijing 7.9 °C
(2006) 2002
Maximum: 8.1° C Nocturnal UHI in March
Tokyo Saitoh et al (1996)
Mean: 5.3° C 1992
Maximum 8.2 °C 25-28 May 2008
Delhi DELHI-I
Mean: 4.7 °C


Urban Heat Islands: Impacts
• Increased energy consumption:
– Higher temperatures in summer increase energy demand for
cooling and add pressure to the electricity grid during peak periods
of demand.
• Compromised human health and comfort
– Warmer days and nights, along with higher air pollution levels, can
contribute to general discomfort, respiratory difficulties, heat
cramps and exhaustion, non-fatal heat stroke, and heat-related
mortality.
• Elevated emissions of air pollutants and greenhouse gases
– Increasing energy demand generally results in greater emissions of
air pollutants and greenhouse gas emissions from power plants.
Higher air temperatures also promote the formation of ground-
level ozone.

Conclusions
• The urban heat island effect is prevalent in Delhi and its magnitude
has been observed to be of the order of about 8°C.
• Maximum UHI was observed at dense residential and commercial area
of Sitaram Bazar during nighttime. Other stations with highest UHI
were Bhikaji Cama, Connaught Place, and Noida.
• Comparison with maximum and average UHI of other cities of the
world revealed that UHI in Delhi is comparable to other major cities of
the world such as London, Tokyo and Beijing.
• More field campaigns at higher spatial resolution and longer duration
along with satellite data would provide greater insight .


References
• Mohan M, Pathan SK, Kolli NR, Kandya A, Pandey S. (2011) Dynamics
of Urbanization and Its Impact on Land-Use/Land-Cover: A Case Study
of Megacity Delhi, J Environ Prot 2: 1274-1283
• Mohan M, Kandya A, Battiprolu A (2011) Urban Heat Island Effect
over National Capital Region of India: A Study using the Temperature
Trends. J Environ Prot 2:465-472.
• Mohan M, Kikegawa Y, Gurjar BR, Bhati S, Kandya A, Ogawa K (2009)
Assessment of Urban Heat Islands Intensities over Delhi. The Seventh
International Conference on Urban Climate (ICUC-7), June 2009,
Japan.


Urban heat islands

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Urban heat islands

Ähnlich wie Urban heat islands (20)

Mehr von Delhi2050

Mehr von Delhi2050 (13)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Urban heat islands