Macro and micro climate

CLIMATOLOGY - I
DEPARTMENT OF ARCHITECTURE
NORTH-EASTERN HILL UNIVERSITY

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Macro and Micro Climate ……
CLIMATE
The climate of the Earth consists of a series of interlinked physical
systems powered by the sun. In the built environment we are generally
concerned with local climatic systems in particular.
• Macro – Climate the climate of a larger area such as a region or a
country
• Micro – Climate the variations in localized climate around a building

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Macro and Micro Climate ……
• The macro and micro climate has a very important effect on both the
energy performance and environmental performance of buildings –
both in Summer and Winter season.
• The site and design of a building can have a profound effect upon
the interaction between a building and its environment.
• The building site affects exposure to the prevailing wind, pollution
levels, solar radiation that the building receives, temperatures and
rain penetration.

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Site and Macro Climate ……
• The orientation of the building affects solar gains and exposure to
the prevailing wind (ventilation).
• The location of neighboring trees and buildings affects the solar
gains (shading) and wind patterns.
• Neighboring trees and buildings also protect the building from
driving rain.

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Macro Climate ……
• The macro climate around a building cannot be affected by any
design changes.
• The building design can be developed with a knowledge of the
macro climate in which the building is located.
• General climatic data give an idea of the local climatic severity:
Seasonal accumulated temperature difference (degree day) are a measure
of the outside air temperature, though do not account for:
a. Available solar radiation.
b. Typical wind speeds and direction.
c. Annual totals of Global Horizontal Solar Radiation.
d. The driving rain index (DRI)

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• This Meteorological data gives a general impression of the climate
at the site of a building and the building design can be planned
accordingly.
• However the building itself and surrounding geography will affect the
local climate.

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• This Meteorological data gives a general impression of the climate
at the site of a building and the building design can be planned
accordingly.
• However the building itself and surrounding geography will affect the
local climate.

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Micro Climate ……
• The site of a building may have its own micro climatic conditions
caused by the presence of hills valleys, slopes, streams and other
buildings.
Micro Climate - Effect of Local Terrain
• Surrounding slopes have important effects on air movement,
especially at the bottom of a hill. In the hills air warmed by the solar
radiation rises upwards due to buoyancy effects (Anabatic flow), to
be replaced by cooler air drifting down the slope (Katabatic flow).
• The result is that valley floors are significantly colder than locations
part way up the slope.

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Micro Climate - Effect of Local Terrain
• Katabatic flows often result in frosts
persisting for longer in low lying
locations.
• The most favorable location in a
valley is known as the thermal belt,
lying just above the level to which
pools of cold air build up, but below
the height at which exposure to wind
increases.
• The crests of hills and ridges have
unfavorable wind velocity profiles,
the wind flow is compressed (as
happens with an aero foil) leading to
high wind velocities.

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Micro Climate - Effect of Buildings
• Buildings contribute to create micro-climatic conditions by shading the
ground, changing wind flow patterns.
• One example of how buildings affect the local climate is the heat island
effect in large cities where the average temperature is higher than the
surrounding areas.
• Solar energy absorbed and re-emitted from building surfaces,
pavements roads etc. creates a warming effect on the surrounding air.
• Also the large quantities of buildings break up the wind flow, reducing
wind speeds and causing the warm air to remain stagnant in the city.
• This also causes increased pollution as well as temperatures.

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Micro Climate – Urban Heat Islands
• “An urban heat island (UHI) is a city or metropolitan area that is
significantly warmer than its surrounding rural areas due to human
activities.”
• The phenomenon was first investigated and described by Luke
Howard in the 1810s, although he was not the one to name the
phenomenon.
• The main cause of the urban heat island (UHI) effect is from the
modification of land surfaces, which use materials that effectively
store short-wave radiation.
• The less-used term heat island refers to any area, populated or not,
which is consistently hotter than the surrounding area.

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What is an Urban Heat Island ?
As urban areas develop, changes occur in their landscape.
Buildings, roads, and other infrastructure replace open land and
vegetation. Surfaces that were once permeable and moist become
impermeable and dry. These changes cause urban regions to
become warmer than their rural surroundings, forming an "island"
of higher temperatures in the landscape.

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Micro Climate …… Heat Island

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Micro Climate …… Heat Island

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Where does Heat Island occur ?
Heat islands occur on the surface and in the atmosphere. On a hot,
sunny summer day, the sun can heat dry, exposed urban surfaces,
such as roofs and pavement, to temperatures 50–90°F (27–50°C)
hotter than the air, while shaded or moist surfaces—often in more
rural surroundings—remain close to air temperatures. Surface urban
heat islands are typically present day and night, but tend to be
strongest during the day when the sun is shining.

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Micro Climate …… Developed Environment
• Urban, suburban, and rural communities are the three main types of
developed environments.
• All three of these environments have both common and unique land
cover types. Each land cover may affect local air temperatures
differently because of unique thermal properties.
• These areas have natural surfaces and impervious surfaces.

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Micro Climate …… Developed Environment
Impervious surface: A hard surface area that either prevents or retards
the entry of water into the soil as under natural conditions prior to
development
and/or
a hard surface area that causes water to run off the surface in greater
quantities or at an increased rate of flow from the flow present under
natural conditions prior to development.
 Common impervious surfaces include, rooftops, walkways, patios,
driveways, parking lots, storage areas, concrete or asphalt paving,
gravel roads, packed earthen materials, and oiled, macadam, or other
surfaces that similarly impede the natural infiltration of urban runoff.

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Why do we care about Heat Islands ?
Heat islands can affect communities by increasing
summertime peak energy demand, air conditioning costs,
air pollution and greenhouse gas emissions, heat-related
illness and mortality, and water quality.

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High energy demands
Increased energy consumption: Higher temperatures in
summer increase energy demand for cooling and add pressure
to the electricity grid during peak periods of demand. One study
estimates that the heat island effect is responsible for 5–10% of
peak electricity demand for cooling buildings in cities.

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Increased Emissions
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.

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Quality of life
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.

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Water Quality
Impaired water quality: Hot pavement and rooftop
surfaces transfer their excess heat to storm water, which
then drains into storm sewers and raises water
temperatures as it is released into streams, rivers, ponds,
and lakes. Rapid temperature changes can be stressful to
aquatic ecosystems.

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What can be done ?
Communities can take a number of steps to reduce the
heat island effect, using four main strategies:
• Increasing tree and vegetative cover
• Creating green roofs (also called "rooftop gardens" or
"eco-roofs")
• Using cool or green pavements
• Installing cool or reflective roofs

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GREEN ROOF
• A GREEN ROOF is a roof of a building that is partially or
completely covered with vegetation and soil, or a growing
medium, planted over a waterproofing membrane.
• The term "GREEN ROOF" may also be used to indicate roofs
that utilize some form of "green" technology, such as solar
panels or a photovoltaic module.
• Green roofs are also referred to as eco-roofs, vegetated roofs,
living roofs, and green roofs.

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GREEN ROOF
R E N Z O P I A N O

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CALIFORNIA ACADEMY OF SCIENCES
OR REENE PAIN RAE
BIIN - EE

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HE IVIN ROOF

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COOL PAVEMENTS – pervious pavements
• The term refers to materials chosen to reduce pavement
temperature by increasing pavement reflectivity (Albedo
Effect) or controlling temperature by other means through
choice of materials and engineering design.
• Pervious pavements can be made of concrete, asphalt, open-
celled stones, and gravel, that are mixed in a manner that
creates an open cell structure allowing water and air to pass
through.

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COOL PAVEMENTS – pervious pavements
Advantage
• Pervious pavements allow rainwater to seep into the ground through
the pavement:
– Vegetation is watered, reducing the need for irrigation
– Ground water is recharged
– Water resources are preserved
– Storm water runoff is reduced
– Storm water runoff quality is improved

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Improving Micro Climate through Design
The aims of enhancing Micro-Climate around Buildings:
• Reduce costs of winter heating.
• Reduce summer overheating and the need for cooling.
• Maximize outdoor comfort in summers as well as winters.
• Improve durability of building material (reduced rain penetration).
• Encourage growth of plants.
• Facilitate open air drying of clothes.

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Means of enhancing the micro climate around a building include:
Solar Access:
• Allow maximum daylight into space and buildings.
• Allow maximum solar radiation into space and buildings (For Cold
areas).
• Shade open spaces and windows from prolonged exposure to
summer sun.
• Protect space and windows from glare.

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Means of enhancing the micro climate around a building include:
Wind Protection:
• Protect space and buildings from prevailing winds and cold winds.
• Prevent buildings and terrain features from generating turbulence
• Protect spaces and buildings from driving rain and snow
• Protect space and buildings from katabatic flows, while retaining
enough air movement to disperse pollutants.

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Means of enhancing the micro climate around a building
include:
Features:
• Provide thermal mass to moderate extreme temperatures.

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include:
Features:
• Use vegetation for sun shading and wind protection (transpiration
helps moderate high temperatures).

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• By altering wind movement, evaporation, moisture, and soil temperatures,
vegetation influences the microclimate of an area, especially near the
ground.
• Temperatures at ground level in the shade are lower than those in places
exposed to sun and wind.
• Vegetation reduces the steepness of the temperature gradient above the
ground surface and influences relative humidity and the height of the active
surface, the surface of any object that receives or is impacted directly by
solar radiation.
• Vegetative cover will also influence the extremes and daily maximum and
minimum temperatures.
Micro Climate …… The Importance of Vegetation

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include:
Features:
• Provide surfaces that drain readily.

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include:
Features:
• Provide water for cooling be evaporation (pools & fountains).

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Factors Affecting Micro Climate
WITHIN DESIGNER’S LIMIT BEYOND DESIGNER’S LIMIT
• Spacing and orientation of buildings • Area and local climate
• Location of open spaces • Site surroundings
• Form and height of buildings • Site shape
• Fenestration • Topographic features
• Tree cover , Ground profiling, wind
breaks, surrounding surfaces (grass
pavers etc.)
• Surrounding buildings

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Two main possibilities for influencing Micro Climate are Solar Access and
Wind Control.
Solar Access:
• Solar access to a site is often a case of minimizing solar overheating in
summer while maximizing solar access during the winter.
• Buildings with a heating requirement should be orientated north south with
maximum glazing on the south face.
• Deciduous trees offer an excellent means of site shading, with shading
being reduced in winter when the trees lose their leaves.
• The colour of surrounding surfaces will have a pronounced effect on the
solar radiation available to the building – Albedo Effect

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Two main possibilities for influencing Micro Climate are Solar Access
and Wind Control.
Solar Access:
• Light coloured paving will increase the radiation reflected from the ground
into the building.
• Paving stones will also provide external thermal mass, moderating
temperature swings immediately adjacent to the building.
• Grass planted outside a building will reduce the ground reflected solar
radiation – thus trapping heat – Heat Island Effect
• Use of courtyards and water can also moderate the effects of high
temperatures on summer.

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Two main possibilities for influencing Micro Climate are Solar Access and
Wind Control.
Wind Control – The form of the building can have a great effect on the impact of
wind.
• Avoiding of funnel-like gaps between buildings.
• Avoiding abrupt changes in building heights.
• Orientate long axis of the building parallel to the direction of the wind
• Use pitched rather than flat roofs and stepped forms for higher buildings
• Groups of buildings can be arranged in an irregular patterns to avoid wind
tunneling.
• Coniferous trees and fencing and other landscape features such as mounds of
earth and hedges can also reduce the impact of wind and driving rain on the
building.

Macro and micro climate

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