Climate change is one of the most challenging
global environmental issues facing humanity in this century. Climate change
mainly arises from global warming that is created by societal activities such
as combustion of fossil fuels and land use changes that also have wide-ranging
consequences to our natural world and to human settlements all around the
world. With all of its manifestations and components, global warming is profoundly
a local issue and can have its effects in urban as well as rural areas. It is
in this context, that urban centres play a crucial role in the climate change
arena (Satterwhite, 2008).
According to Patz
and Balbus, (2003), numerous cities will probable face more problems with
certain air pollutants as concentrations of air pollutants change in response
to climate change because a portion of their formation depends, in part, on
temperature and humidity. ConcerningBN1
urban heat islands, higher temperatures occur in urban areas than in outlying rural
areas because of diurnal cycles of absorption and later re-radiation of solar
energy and (to a much lesser extent) heat generation from built/paved physical structures
increasing the frequency and severity of heat-stress events in cities.
Beyond the risks and vulnerabilities that
climate change brings about in urban centres, these same urban centres play a
pivotal role in the mitigation and adaptation efforts as well. They are hubs of
development, sources of innovations and policy responses to reduce the
emissions of heat trapping gases and adapt to the impacts of climate change. It
is this combination, within urban areas, of increased vulnerabilities along
with increased opportunities that can incubate important synergies and resources
for creating innovative climate change adaptation and mitigation strategies.
The urban environment offers distinctive
biophysical features in relation to the surrounding rural areas. These include
an altered energy exchange that create urban heat island, as well as changes to
hydrology such as increased surface runoff of rainwater. Such changes are, in
part, a result of the altered surface cover of the urban area due to overall
urbanization process. For example, less vegetated surfaces lead to a decrease
in evaporative cooling, whilst an increase in surface sealing results in
increased surface runoff and climate change is set to amplify these distinctive
biophysical changes are, in part, a result of the altered surface cover of the
urban area (Whitford et al., 2001). Urbanization replaces vegetated surfaces,
which provide shading, evaporative cooling, and rainwater interception, storage
and infiltration functions, with impervious built surfaces. However, urban
greenspaces provide areas within the built environment where such processes can
take place (Whitford et al., 2001).
changing climate, the benefits provided by urban greenspace becomes
increasingly important. For example,
trees are felled for the perceived threat they pose near highways and buildings
(Biddle, 1998), infill development takes place on former gardens, front gardens
are paved over to provide parking spaces for cars, and biodiverse urban
‘wasteland’ is earmarked for redevelopment (e.g. Duckworth, 2005; GLA, 2005;
Pauliet et al., 2005). Urban green space has far greater contribution
to mitigating against future climate change, which is currently underdeveloped.
Urban green spaces presently produce enormous environmental benefits, which are
currently undervalued. These benefits include improving air quality and
temperature by creating cooling effects through evapotranspiration, storing and
reradiating less heat than built surfaces, and through direct shading (Gill,
2006), promoting biodiversity; and many others. Increasing the green space,
especially in densely built-up areas is considered a valuable adaptation
response in order to reduce the threat extreme and high temperatures to human
health and comfort.
development has to meet the challenge of establishing adaptation strategies in
response to climate change. In view of its potential to regulate urban
climates, green infrastructure will assume a critical role in these strategies.
In addition to their positive microclimatic effects, as a source of cooling in dense,
hot cities urban green spaces can contribute to mitigation. They can operate as
carbon sinks or can reduce energy consumption for air conditioning by providing
shade by urban trees or rooftop greenery. Thus, urban green spaces should be
incorporated as a significant component into both adaptation and mitigation
study will focus on investigating the role-played by urban green spaces in
climate change adaptation and mitigation. It will focus on modelling of
temperatures and green space cover, assessing the opportunities and vulnerability of urban greenspace to influence
climate change at the city and neighbourhood level, more
specifically in the reduction or mitigation urban heat island.
1.2 Statement of the problem
One of the
main problem in Nairobi today is the uncontrolled, haphazard development of the
city. According to EPA (2005), the temperatures in urban areas are higher to
suburban areas. As cities develop, natural landscapes are replaced with paved
areas, surfaces and buildings. Impervious surfaces such as parking lots, roofs
and roads attract the greatest amount of heat as well as the large masses of
reinforce concrete, steel structure buildings absorb and produce huge amounts
of heat which in turn is radiated to the surroundings.
intensity of UHI varies from one city to another or from one part of the city
to another. Commercial centers are mostly experience some degrees warmer than
the areas around the cities. The situation in cities/urban areas is obviously
more complex, following modification of the atmosphere by urbanization,
pollution dispersion takes place in a different manner from that of observed in
physical expansion has fueled the increasing population; in the last two
decades making Nairobi to be one of the most extensive of any city in
sub-Saharan Africa, with probable no further room for spreading out. The rapid
horizontal expansion has created vast and a chaotic urban sprawl that has and
is putting severe constrains on an already creaky city infrastructure and
resulting in serious environmental degradation. Consequently, the city has/is
being occupied by multi-storey buildings and high commercial buildings that
dominate the skyline creating an intense effect on the city microclimate. These
continuous constructions in the city have replaced its lush gardens and
greenery. Furthermore, human activities (urbanization) in Nairobi intensify the
amount of heat produced due to the transportation systems, industrial plants,
and heating ventilation and air conditioning (HVAC) systems that are installed
for cooling the building to lower the internal temperature to suit human
thermal comfort inside the buildings. As a result, the urbanization and human
activity are major factors in increasing the intensity of UHI and contribute
significantly as one of the reason of the UHI.
today is under the pressure of urbanization and climatically factors.
Especially in summers, raised temperatures derive from the using of low albedo
material in urban spaces and increasing numbers of buildings and construction
in city causes decrease in trees and vegetation. Therefore, in high-density
areas air temperatures increases beyond the norm. Lack of greenery, generally
and low quality of albedo facades in urban spaces are quite important issues of
the HI intensity in the city of Nairobi.
Aims and Objectives
The two principal aims of this research
are to; i) assess the opportunities and vulnerability of urban greenspace in
mitigation and adaptation to climate change at the city and neighborhood level,
more specifically in the reduction or mitigation of urban heat island through utilizing remote sensing and GIS tools to detect,
analyse and map spatial patterning and attributes of UGS,
calibrating the surface temperatures in relation to greenspace patterns and
attributes and ii) to test options for soft engineering to utilize the
moderating influence of greenspaces to reduce climate change impacts on people
To achieve these aims, the research will
be broken down into four objectives
1. Determine the dynamics and extent of urban
greenspaces in the study area over a period of 32 years in three-time periods
with base year of 1986.
2. To estimate quantitatively the continuous
air temperatures in the study area over a period of 32 years in three-time
periods with base year of 1986.
3. Investigate the opportunities and
challenges of urban green spaces in mitigation and adaptation of urban area to
4. Investigate the mitigation and adaptation
responses of utilizing urban green spaces in urban areas.
Previous studies have largely focused either on heat island intensity or
on the physical determinants of urban heat islands, or on the spatial
distribution of heat-vulnerable across populations (Taha 1997, Simpson &
McPherson 2007, Arnold &Gibbons2007, Jones et al. 2007, Grimm et al. 2008, Grimmond,
2007, Watkins et al. 2007, Howard 1833, Ongoma et al, 2016,) .These studies revealed that temperature
differential is largely attributed to the historic discovery that the increased
vertical dimension of cities such as taller buildings promotes an increased
absorption of latent heat, furthermore increasing the average temperatures of cities.
Changes in land-cover, from open grasslands
and woodlands to built cities increases the amount of impervious surfaces and simultaneously
decreases natural vegetation and soil coverage, thus decreasing the vegetative evaporative
cooling process. Additionally, higher thermal intensity increases energy
demands for air conditioning buildings creating a positive feedback loop that
relies on a continuously growing energy demand and subsequent temperature
increases, ultimately perpetuating UHIs vulnerability.
However, despite the existence of information on urban heat island effects,
there is limited information on measurement and monitoring of the mitigation
and adoption role played by urban green spaces in over most cities in
developing countries especially in Africa, the city of Nairobi and Kenya at large
(Ongoma and Muthama, 2014). Generally, limited urban climate studies have been carried
out in developing countries. Most studies that have been conducted in the
countries focus on urban and non-urban temperature differences; this is partly
explained by limited data. Studies on the impact of urban green spaces on
mitigating UHI are very few. Although Ongoma and Muthama (2014) reported that the
larger county of Nairobi does not experience heat stress throughout the year,
the study was carried out over a short period, and in the ongoing socioeconomic
development and global warming, there is need of continued study and monitoring
of thermal comfort in the city. The aim of this study is to assess the role of
urban green spaces in mitigating and adapting to UHI effects over Nairobi city.
Consequently, the study will serves as baseline for urban planners, structural
designers and local authorities to rethink the roles played by urban green spaces
in mitigation the effects of UHI to enhance human comfort in the city of
Nairobi by designing adequate mitigation strategies to climate related risks.
will focus on Nairobi city, the largest and capital city of Kenya, covering an
area of 696 km2 with an estimated population of 4,235,000
(UN Projections, 2012) inhabitants at the close of 2017. It lies in between
latitude 1?16’59” South: Longitude 36?49’00” East, with an elevation of 1684m
above the sea level.
a subtropical highland climate. At 1,684 meters above sea level, evenings may be
cool, especially in the June/July season, when the temperature can drop to 9 °C
(48 °F). The sunniest and warmest part of the year is from December to March,
when temperatures average the mid-twenties during the day. The mean maximum
temperature for this period is 24 °C (75 °F). There are two rainy seasons, but
rainfall can be moderate. The cloudiest part of the year is just after the
first rainy season, when, until September, conditions are usually overcast with
drizzle. As Nairobi is situated close to the equator, the differences between
the seasons are minimal. The seasons are referred to as the wet season and dry
season. The timing of sunrise and sunset varies little throughout the year for
the same reason.
The city is
considered to be fully urbanized with most surfaces covered with tarmac,
buildings and other impervious surfaces. There is maximum land use with minimum
vegetation cover compared to the surrounding area. The colonial 1948 Master
Plan for Nairobi still acts as the governing mechanism when it comes to making
decisions related to urban planning. The Master Plan at the time, was designed
for 250,000 people, allocated 28% of Nairobi’s land to public space inclusive
of the green spaces, but due to rapid population growth, much of the vitality of
public spaces within the city are increasingly threatened by private
Recent studies conducted in
Nairobi city indicates that is a reduction in wind speed and relative humidity
over the city, posing threat to human and animal comfort and the environment at
large. The city of Nairobi, just like other cities globally is observed to
experience urban heat island (UHI) with an observed increase in minimum
temperature as compared to maximum temperature signifying an overall warming
(Ongoma et al., 2016). The reflectivity of the city ranges between 0.12 and
0.15 (Ongoma, 2012). Muthoka and Ndegwa (2014) studied the dynamism of land use
changes on surface temperature over Kenya, focusing on Nairobi city. The study
showed a reduction in vegetation cover to bare land or built-up; an evidence of
a growing city.Njoroge et al. (2011) assessed the landscape change and
occurrence at watershed level in city of Nairobi. The study observed
significant changes in the spatial configuration of the landscape of Nairobi
city between 1976 and the year 2000. According to the study, land use related
to human activities such as built areas increased to the detriment of wetland
and vegetated areas, signifying the city’s growth. Ongoma et al., (2012, 2013a)
and Makokha and Shisanya (2010) observed increase in both minimum and maximum
temperature of the city of Nairobi
The study will employ a three-part
Firstly, an assessment of the land cover
characteristics to determine the extent and spatial patterns and attributes of
the urban green spaces. The land cover will be categorized into four surface
cover types (buildings, roads and other impervious surfaces, green spaces,
water and bare soil/gravel) using the AFRICOVER classification scheme, Landsat
Imagery and aerial photography of Nairobi. Interpretation of aerial photography
will enable the identification of the surfaces that potentially could be
greened either fully or partially in the future.
Secondly, continuous air temperature will
be investigated from satellite imagery, weather station ground observations
utilizing ArcMap and Erdas Imagine software. This process will entail four
of top of atmosphere, or at-sensor, brightness temperature;
of ground surface emissivity; and
of the mono window algorithm for land surface temperature retrieval. The mono
window algorithm to be used in this study was developed by Qin et al.
(2001), and was selected over other methods of surface temperature
estimation—such as the temperature-emissivity separation algorithm or the
split-channel method—due to its relatively negligible input data requirements.
an energy exchange model will be developed to analyze future projected surface
temperatures. The model will built based on the principles of the energy
exchange model developed by Tso (1990; 1991) that is based on an energy balance
equation, providing outputs of maximum surface temperature.
Thirdly, structured interviews will be
carried out with the urban experts comprising of environment experts, urban
planners within the city, and academicians in the fields of urban planning and
management, environmental studies as well as selected residents from different
parts of the city to investigate the influence of urban green spaces on climate
6. Research Timeline
STAGES OF STUDY
Problem Statement, Aim, Objective formulation
Data input and analysis
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