Landscape Planning for Climatic Adaptation in hot arid climatic zones
Imad Kayyali
Preface:
There are not different “kinds” of architecture, but only different situations, which
require different solutions in order to satisfy man’s physical and psychic needs.
Man dwells when he can orient himself within and identify himself with an
environment, or, in short, when he experiences the environment as meaningful.
Dwelling therefore implies something more than “shelter”. It implies that the spaces
where life occurs are places, in the true sense of the word. A place is a space, which
has a distinct character. Since ancient times the genius loci, or “spirit of place”, has
been recognized as the concrete reality man has to face and come to terms with in
his daily life.
Christian Orberg-Schultz
This article summarizes a project research that has been conducted in some Gulf country. The site was
distinguished with its extreme dry and hot climate, in addition to the dust storms, which blow in spring
and summer each year, resulting sand erosion and very uncomfortable weather conditions. These
conditions may cause some problems for the labors that will be in site during construction.
Our team’s idea was to protect the site through the landscape planning, before any construction works
being curried out on site. Our main target that could become our main achievement was to minimize the
effects of the harsh climate generators, in addition to increase all those elements that may beco- me
moderating factors and provide comfort for the work site.
In response to Dubai Municipality’s plan on the continuous training program, this study has been enriched
recently, with additional text on the climate that distinguishes Dubai and a high percentage of the UAE
area while still part of the hot arid climate area, this climate witnesses high humidity.
The article manifests two parts: The first part demonstrates in summary the general topics of landscape
architecture. The second sheds lights on landscape planning for climatic adaptation, with special emphasis
for the hot arid climate zone.
Imad M. Kayyali
Dubai, 1999.
Part One: Landscape Architecture:
1.1 Introduction:
While architects are involved with the design of buildings and their immediate surroundings, landscape
architects are concerned with the design and preservation of the whole outdoor natural elements:
topography, vegetation, water surfaces, Ecology, etc, that should make man’s outdoor life more
comfortable, & afford him with means that help him to resist natural dangers such as: frost, floods, dust &
precipitation, etc. as well as man-made effective elements, such as: pollution & noise, land forms & water
features, beside facilitating man with recreational areas, pathways, street furniture & others.
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Landscape architecture has been developed through history, in parallel with architecture. Landscape
styles were related to regions, cultures or historical eras, such as: Ancient Egypt, Mesopotamia, Greece,
Romans, Islamic World, middle Ages, Renaissance, Baroque, China, Japan, India, etc.
New movements have appeared in the late 1960s in several regions, that concluded landscape types into
the following defined categories.
a- Formal Geometric Landscape b- Rustic Landscape
c- Natural and Desert Landscape. d- Transitional Landscape
e- Tropical Landscape f- Oriental Landscape.
g- Woody Landscape.
Eventually, Landscape Architecture comprises the following two parts:
a- Hard Landscape: which is concerned with man-made elements, such as paving, sidewalks,
streets, parapets, decks, gazebos, etc.
b- Soft Landscape: Which deals with plant materials and vegetation: trees, shrubs, vines, ground
covers, etc.
1.2 Plants:
The Plant Kingdom is usually categorized into the following:
a- Annuals, b- Non-flowering (ferns) & Herbaceous perennials (Bulbs) c- Biennials.
d- Woody Perennials- Flowering plants (Permanent).
For landscape purpose, plant materials are sorted out into:
a- Trees b- Shrubs c-Bushes
d- Vines e- Ground Covers and Lawns f- Bulbs, Ferns & Annuals.
Trees and shrubs are usually either Deciduous or Evergreen, where deciduous stands for those species
which loose their leaves in winter.
1.3 Site Analysis:
Prior to the design process get started, a full site analysis shall be conducted, comprising site geology,
slopes, ecology, soil, vegetation, climate, aquifers & infrastructure. Analyzing this information shall lead to
the best adaptation to site restrictions, potentials & requirements.
Part Two: Landscape Planning for Climatic Adaptation in Hot Arid Climate.
2.1 Introduction:
In the ancient times, it was said that man’s life pattern is dependent upon the climatic conditions
in which he finds himself. Environment dictates man’s means of livelihood, home, food and
clothing
People believe that the proper climatic conditions were the main stimulus for the development
of civilizations, also it is believed that workers productivity declines in climates of excessive heat
or cold.
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Hence, we are getting closer to the question: can man control his environment? In spite of the
great choices offered by modern technology in order to facilitate man with means so as to
sustain excessive climatic conditions, it became quite improper to rely on those artificial means
that have side effects upon man’s environment. Beside, communities are loosing natural
resources through the extensive use of modern technology.
During last decades, man began to look for natural elements those can modify his micro-climate.
The relatively new expression of “micro-climate” describes the climatic conditions of a very local
area or place, such as a hillside or an in-house courtyard, which are smaller in scale than the
Mesoclimate and the Macroclimate scales. The micro-climate shall not confuse the reader with
the microclimate expression, which describes the microscopic scale of climatic conditions.
The following table illustrates the principal climatic scales:
Climate Scale Example
Macro-climate Extremely Large Continent, Country
Meso-climate Country, City
Moderate
Micro-climate Small City block, Lot, Garden
Microclimate Extremely small Leaf, sidewalk crack
2.2 Climatic Impact of Natural and Man-made Elements:
2.2.1. Climate Generators:
Before discussing the natural elements affecting micro-climate areas, it’s quite helpful
to have a look on the main generators of climate affecting man’s comfort. These
generators are:
i- Solar Radiation: moving through the atmosphere, solar radiation may:
a- Reflected back into space.
b- Dissipated within the atmosphere.
c- Diffused through the atmosphere.
d- Strikes the earth’s surface.
Energy is transferred through, Radiation, Conduction
and Convection. Radiated Heat transfers at the
speed of light in the form of electromagnetic waves.
The other forms of heat transfer are much slower
and need a media to transfer.
The dynamics of the solar movement shall be
analyzed for best shading.
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ii- Winds: Moving over the earth’s surface, they encounter of impediments which:
detract, deflect, obstruct and lessen the impact of speed of the flow of the
unobstructed wind.
Wind movement can be (a) Laminar (Steady), (b) Turbulent (Random Pattern and
unpredictable) or (c) Separated. Air movement is affected by its inertia, friction with
surrounding elements and differences in pressure and temperature.
The major groups of winds are:
a- Tropical Easterly of Trade Winds.
b- The Mid-latitude Westerly.
c- Polar Winds.
iii- Precipitation and Humidity: Rain, Snow, Moisture, Evaporation, Dew and Frost.
Atmospheric Humidity can be measured in three different ways:
a- Absolute Humidity: g/m3 of air
b- Specific Humidity: g/kg of air.
c- Vapor Pressure: Bars of Water Weight.
d- Relative Humidity RH: Actual/ Saturated %
2.2.2 Man Made Elements (Hard Landscape Materials)
Different Materials have variable responses to sun radiation, in what we call “Specific
Heat”. On the other hand, some of the material’s properties may alter the material’s
response against sun radiation. Those properties are, Mass, color, texture, exposed area,
location, orientation, etc.
Therefore, our landscape materials are categorized according to their abilities to reflect,
radiate and transmit solar radiation.
We hereby list some selected materials together with their relative reflectivity % of sun
radiation, taking into consideration that these figures may vary as mentioned above in
connection with other parameters such as color and texture:
Asphalt 12% Brick
50%
Concrete 40% Dark Forest 05%
Desert 25% Dry Grass 30%
Green Forest 09% Oak woodland 17%
Green Leaves 30% Green Fields 12%
High Fresh Grass 25% Rock 12%
Dry Sand 27%
2.2.3. The Natural Elements:
Landforms and vegetation are considered to be the major natural elements that may
affect the micro-climate:
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a- Landforms: Landforms can be either of large, medium or small scale.
Landforms may affect air movement through deflection, impeding airflow pattern, velocity, quality
and quantity.
b- Vegetation: The effectiveness of special plant materials in climate
control depends upon the forms and character of the plant, the climate
of the region and the specific requirements of the site.
 Vegetation may absorb 90% of the light falling on it.
 Vegetation can filter, guide, obstruct, reduce or accelerate winds.
 The optimum density of vegetation for wind control (by ASLA) is 50-60%
 Vegetation may reduce wind speeds in an area to less than 10% of that in
the open, or increase them, reduce day time temperature by as much as
8.5°C, and in certain situations, raise night time temperature.
The main uses of vegetation of special importance to the energy- conscious
designers are:
1- Large trees and shrubs: screen out undesirable winds and evergreen trees of high
dense leaves should be used to control winter winds.
2- Trees: channel winds to increase ventilation.
3- Plantings: Reduce snow accumulations on ground.
4- Vegetation: Especially needle leave trees: capture fog, increase sunlight reaching
ground.
5- Deciduous Trees: Screen sunlight in summer, then reduce required cooling loads and
allow it to pass in winter, then reduce required heating loads.
6- Planted Areas: Will be cooler during day, then heat loss at night will be less, then
razing specific heat of area.
7- Precipitation increases in forest areas.
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2.3 Temperature Control:
a- Solar Radiation Control:
Vegetation provide solar radiation control through:
Absorbing, Reflecting, Radiating and Transmitting.
The Major effect of the forest on any climatic factor is
reduction of short wave radiation by 73-80%. The forest
can reduce monthly maximum air temperature in the
summer by 6.5°C, reduce annual rain fall (through
interception) by 15-30% and wind velocity by 20-60%.
b- Wind Control:
The most interest wind is that blowing at 1.8-2.5 m High.
But it is effective up to 18 m.
Planting affect air flow in the following ways:
1- Affecting Wind Movement.
2- Affecting amount of airflow.
3- Changing air direction.
4- Has no effect on lees side of a building, but may perform as an obstacle when applied on an
outlet opening.
Wind velocity control is a principal factor that needs to be modified so as to reduce energy used
in either heating or cooling. For example, heating load with a 36-km/h wind is 2.4 times as 10-
km/h wind (without protection). When protected, it would be twice only. For hot humid climate,
wind control is the vital factor that has to be considered for ventilation.
Notes on wind breaker trees and hedges:
 The taller the trees are, the more raws
required, as tree gets naked trunk taller as it is
taller, which allow for low height streams of
wind.
 Width affects only penetrability.
 Irregular windbreakers (mixture of trees) are
more effective.
 Trees of pitched edges are less effective.
 The most effective ratio of height to protected
length is 1:11.5.
 The optimum density for a shelter belt is about
50-60%.
 Parallel shelterbelts, spaced widely apart, have no acomm-ulative effect on reducing wind
velocity. But closer ones do.
 Plants should be located to protect buildings from expected directions.
2.4 Water
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Seas, Lakes and Rivers are preferable for people... for amusement, picnics, recreations and
adventures, in addition to transportation.
People like to be near water surfaces because they can enjoy skating, sailing, fishing, swimming,
sinking, etc. However, they like it also because of the cooling effect that water bodies provide in
the surrounding area.
Old Arabs have practiced another experience with water features, such as: fountains, ponds,
channels, etc. In order to modify the micro- climate of places like the “Dorqua” by adding
humidity to the dry air in summer and cooling it by investing the high specific heat of water,
which cause less variation of pattern of temperature between day and night, summer and
winter.
Therefore, it would be a right decision to use water bodies in the hot arid climate zones, so as to
modify the climate and reduce its extremes through the cooling effect of water and moisture.
Add to that, a small percentage of the solar radiation is radiated off water bodies, that is because
solar radiation is stored deeply underneath surface. Water bodies cause evaporation that would
reduce temperature in the surrounding space.
Airflow in day blows from cooled sea towards warmed land, and at night, from cold land to
cooled sea.
2.5 Hot Arid Climate and Human Adaptation
2.5.1 - Hot Dry Climate:
The main macro features of the hot arid climate are: Clear sky, dry atmosphere, extends
periods of overheating & high diurnal temperature range. Among the principle
parameters of overhea- ting is the formation of the dust particles in the air that absorb
solar radiation & radiates heat through atmosphere.
2.5.1.1 Objectives of Adaptation
1- Block dry dusty wind. Vegetation can clear air through reducing the formation of
clouds of dust and smoke by preventing formation of rising air due to reducing
overheating.
2- Maximize filtered air movement in summer.
3- Maximize humidity.
4- Provide maximum shade, especially in late morning and all afternoon.
5- Create cool and dark micro-climate.
6- Vegetation is desirable as a radiation absorbent surface and for it has evaporative and
shade giving properties.
7- Increase building density.
2.5.1.2 Adaptation
1- Building shouldn’t be sited in narrow valleys, but at lower hillside for maximum
cool airflow.
2- Use decks, as they are less reflective, less hot and allow air circulation
underneath.
3- Winds are to be modified rather than blocked.
4- Streets should be East-West oriented and located to the building’s north side.
For ventilation, Streets shall be perpendicular to winds direction
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5- Orient active living areas to the southeast to collect early morning sun.
6- Optimum orientation is east of South.
7- Glass areas should face south with properly designed overhangs.
8- East and West windows should be avoided to minimize radiation with low sun
angles.
9- Cluster buildings and utilize solar panels for shade.
10- Use deciduous trees in southern elevation.
11- Minimize paved areas, abandon and locate them on the lee side. Color and
texture should be studied.
12- Use vines in south and west walls for shade.
13- Use north and east areas for outdoor activities.
14- Use low conductive, high reflective materials of light color in sun-exposed
surfaces & dark color in shaded surfaces
15- Use water body and locate buildings on the lee side.
16- Use balconies, overhead canopies, courtyards & canopy trees to slow
evaporation.
17- Use ground covers and extensive irrigation.
18- Use dust and draught resistance vegetation.
2.5.2 - Hot arid Climate with high humidity:
It should be understood that this clause sheds light on the Hot Arid Climate that
witnesses high humidity, which can’t be categorized under the Hot Humid (Wet). The
reason behind this confusion is that among the basic principles of climate classification
is the precipitation rates that categorize our two types of dry and humid arid zones
under Hot Arid.
The Main Macro Features that are to be added here are the Humid Atmosphere, Light Winds and Still
Air, Extends Periods of Even Overheating and low diurnal temperature range.
The high amount of water vapor in this climate absorbs more of solar radiation that causes the
uncomfortable feeling. Man can bear a much higher air temperature in the dry weather than he can
do in the humid weather.
2.5.2.1 Objectives of Adaptation
1- Maximize filtered air movement, Speed up Winds.
2- Minimize humidity.
3- Provide maximum shade, especially in late morning and all afternoon.
4- Create cool and dark micro-climate.
5- Vegetation is desirable as a radiation absorbent surface and for it has evaporative
and shade giving properties.
6- Low building density for better air movement.
2.5.2.2 Adaptation
1- Use decks, as they are less reflective, less hot and allow air circulation underneath.
2- Winds are to be modified rather than blocked.
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3- Orient active living areas to the southeast to collect early morning sun. For a
particular site, wind direction shall be considered.
4- Winds shall be enhanced through the use of natural and man-made forms, to
create air pressure differences, thus air movement.
5- Streets shall coincide with wind direction.
6- Optimum orientation is east of South, exact angle shall be studied for the particular
site, taking into consideration the breeze direction. This degree of deviation is
12º-25º.
7- Glass areas should face south with properly designed overhangs.
8- Avoid locating your structures in the low lands, as breeze can be stopped by
windbreakers.
9- East and West windows should be avoided to minimize radiation with low sun
angles. Wind direction shall be considered to catch the breeze.
10- Separate buildings and utilize solar panels for shade.
Use deciduous trees in southern elevation.
11- Streets should be East-West oriented and located to the building’s north side.
12- Minimize paved areas, abandon and locate them on the lee side. Color and texture
should be studied.
13- Use vines in south and west walls for shade.
14- Use north and east areas for outdoor activities.
15- Use low conductive, high reflective materials of light color in sun-exposed surfaces
& dark color in shaded surfaces.
16- Air should enter the building through shaded outdoor areas, avoiding passing
through heated surfaces.
17- Use overhead canopies and canopy trees for shaded pathways. Trees shall be of
high canopy to allow airflow for proper ventilation, as low canopy trees prevent
cooling breeze and trap humidity in pockets of dead air. Trellis has some
advantages on trees, as they don’t need to grow to give the full shade.
18- Use ground covers.
19- Shading Vegetation should not block ventilating winds. Trees shall be located in
parallel to wind direction.
20- Provide Parks in the downtown to reduce concentration of heated air.
21- Equilibrium shall be achieved between the desire of softening the heat load and to
provide unobstructed ventilation of a plot or building.
22- In sloped areas, High positions are more desirable to receive winds. Skyline of
Buildings formation shall be coping with the natural form of the hill that may allow
for a smoother air movement.
23- Parking lots shall be covered with pergolas and deciduous trees.
24- In flat areas, provide more building’s separation for free wind movement.
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