CLIMATIC ELEMENTS AND CLIMATIC ZONES

Objectives

1. Explain the different climatic zones with their defining elements.

2. Understand the effect of climate on human comfort and hence on design.

Climate Macroclimate Microclimate Room Climate

Precipitation Temperature Humidity Wind

Weather is the state of the atmosphere, or the sequence of the states of

the atmosphere at any given time.

Climate the weather conditions prevailing in an area in general or over a

long period

Macroclimate the overall climate of a region usually a large geographic

area —distinguished from microclimate.

Microclimate the climate of a very small or restricted area, especially

when this differs from the climate of the surrounding area.

Wind is simple air movement

In the same way as the earth has a climate, the insides of a buildings also have

climate, room climate, with measurable values for air pressure,

humidity, temperature, velocity of air circulation and ‘internal

sunshine’ in the form of radiated heat.

Efficient control of these factors leads to optimum room comfort and

contributes to man’s overall health and ability to perform whatever tasks

he is engaged in.

Factors in weather

Weather is an collection of all meteorological variables. At any given moment the

elements appear in combination, and it is difficult to determine their relative

importance in the thermal interplay.

The architectural solutions to individual climatic elements should be similarly

blended in a climate balanced structure. To achieve this the importance and

relationships of climatic elements as temperature, radiation and wind effects, which

affect comfort should be established and adapted to the needs of building

practice.

Air temperature

the variation of the diurnal temperature depends on

the state of the sky.

On clear days a large amount of incoming radiation

and a free path for outgoing radiation

produce a wide daily temperature range.

on overcast days the variation is less.

On a seasonal basis the same holds true: clear days in summer are

warmer because more solar energy is received; but a clear day in

winter is usually cooler than a cloudy one, because in the longer

period of nocturnal outgoing radiation heat escapes more easily

through clear atmosphere.

Radiation effects—part of the radiation received at ground level is reflected by

the earth’s surface, but most of the energy is absorbed; it changes to heat and

raises the temperature of the air, the ground and the surrounding objects.

Wind—the effects of wind on housing have to be considered both on the outside and

within the dwelling itself. For comfort balance, air movements have to be evaluated both

as negative and positive. They should be blocked from penetrating structures during

under heated periods but should be admitted and utilized at overheated times.

Climate elements’ basic principles

There are four basic climatic elements. These are:

1. Precipitation includes rain, snow, sleet, hail, drizzle, fog and mist.

2. Temperature is the most important element since it influences other

elements, It depends on geographical factor such as distance from the

equator (latitude) the closer the location to the equator, the warmer the

temperature.

The curve of the earth’s surface affects the angle of the sun’s rays and

how much heat is received. The higher the land (altitude), the colder the

temperature. The temperature increases at 6.5°C every 1,000m above

sea. Air is less dense as it rises and loses heat. The nearer the location

the land is from the sea, the cooler (than average) the temperature is in

summer and warmer in winter, Land heats up and cools down more quickly

than the sea, places inland are warmer in summer and colder in winter,

3. Pressure and winds , winds - the greater the wind, the cooler the temperature,

air pressure is the weight of air resting on the earth’s surface, high pressure occurs

when warm air gets cold, contracts, becomes heavier (denser) and sinks (falls), low

pressure occurs when air is warm, expands, gets lighter and rises, air moves from high

pressure areas and low pressure areas.

This movement of air is wind. The greater the difference between the high and low

pressure, the greater the wind speed. South, facing slopes are exposed to more direct

sunlight than opposite slopes and warmer for a longer period of time.

4. Humidity – the amount of water vapor in the atmosphere. Air can only

hold a certain amount of water before condensation and precipitation

occurs.

Climatic Zones and Building Forms

Architectural buildings must be viewed not only as products in their own right,

but as integral part of the larger environment. That is to say such buildings are

not deemed to be single units, but their functional relationship with man-made

environment, with the natural environment, the surrounding, is solved in a unified

fashion.

Nature adapts from to climate and so do traditions in buildings. The adaptation

stems from the fact that a building heat loss or gain must increase with the area

of surface it exposes to the air outside and there is a thermal argument for

keeping this to a minimum for the volume enclosed. This means a hemispherical

building theoretically, when the environment is to be kept at bay, but practically

for difficulty of other considerations something approaching a cube is an ideal

solution.

For example, in the cold latitudes, the conifer with its short spines is

compact, ’introverted’ sort of tree, closing itself away from the air around it.,

just as the log cabin is compact. In temperate climates, vegetation can merge

more freely with its surroundings, and so can buildings there. Freer planning

still involves some thermal penalty, especially in winter, but it is less severe

and, hence, acceptable if other planning advantages result.

Hot humid climates, the cactus and desert buildings are emphatically back in

compact form. But even in temperate regions, a two-story, i.e. cubic small

house, could be around 20% cheaper to heat in winter than the flatter single-

story version with the same floor area.

Thermally speaking, the house should have no projections on plan, no small

extensions.

Flora Building Form Recommended Layout

Polar zone—igloo

Cold—compact closed

Temperate—can be

more expansive

Hot dry– compact

closed

Hot humid—

expansive, shaded,

ventilated

Microclimate

At ground level multi fold minute climates exists side by side varying sharply with the

elevation of a few feet and within a distance of a mile. Nature demonstrate this in

late winter with melting snow cover patterns, and in early spring when north sides of

hills ,ay be frozen and brown while southerly slopes turn green with awakening

vegetation. Plants are sensitive indicators of favorable circumstances. This effect is

well known to farmers,

Topography and Microclimate

Temperature and the atmosphere decreases with altitude, temperature drop in the

mountains can be approximated as 1°F for each 330’ rising summer and for each 400’ rise

in winter. This effect is important in tropical lands where temperature become more

favorable at high altitude.

As mountains affect the microclimate, small differences in terrain can create remarkably large

modifications in the microclimate. Cool air is heavier than warm, and at night the outgoing

radiation causes a cold air layer to form near the ground surface. The cold air behaves

somewhat like water, flowing towards the lowest points. This “flood of cold air” causes “cold

islands” or “cold puddles”.

Accordingly, elevations that impede the flow of air affect the distribution of the nightly

temperature by dam action; and concave terrain formations become cold-air lakes at night.

Cool air pool

Warm slope zoneRadiating surface and air movement

Natural and Built up Surrounding

Water, having a higher specific heat the land is normally warmer in winter and cooler in

summer, and usually cooler during the day and warmer at night, than the terrain.

Accordingly, the proximity of bodies of water moderates extreme temperature variations,

and in winter raises the minimums, and summer lowers the heat peak. The natural cover

of the terrain tends to moderate extreme temperatures and stabilize conditions through

the reflective qualities of various surfaces. Conversely, cities and man made surfaces tend

to elevate temperatures, as the materials used are usually of absorptive character.

Effects of climate on man

Warm slope zone Radiating surface and air movement Cool air pool Man’s energy and

health depend in large measure on the direct effects of his environment.

It is a common experience to find that on some days the atmospheric conditions stimulate

and invigorate our activities, while the other at times they depress the physical and mental

effort. It is also well known that in certain climatic areas, where excessive heat or cold

prevails energy is diminished by biological strain of adaptation to the extreme conditions

Room Climate

In the same way as earth has a climate, the insides of buildings also have a climate, with

measurable values for air pressure, humidity, temperature, velocity of air circulation and

‘internal sunshine’ in the form of radiated heat. Efficient control of these factors lead to

optimum room comfort and contributes to man’s overall health and ability to perform

whatever tasks he is engaged in.

Climatic Zones in Ethiopia

Ethiopia is a country of varied geographical features; physically the land ranges from sea

level up to 4,500mts above the sea. The altitude has a moderating effect on the climate.

The traditional climatic zones are reflections of the relationship between altitude and

temperature. The traditional climatic zoning does not consider the effct of humidity,

rainfall, and vegetation on comfort.

CLIMATIC ZONES

Zone I– Hot Dry

Lowland

Zone II– Dry Plateau

Zone III– Humid Plateau

Zone IV– Upland

Zone V– Wet Lowland

Location The Hot Dry Zone occupies the northern

Eastern, the extreme north –

Topography It is a vast area flat land within the altitude of

approximately 200-100mt. The depressed area (100mts

below the sea level) is found in this region

Vegetation It is a mixture of desert and semi desert. .In

the lower parts nothing grows. On the higher grounds

some vegetation, like thorn bush, touch isolated grass

clumps with bare patches are found.

Temperature The average daily temperature is 38°C and at night it drops into 21°C . The comfort zone lies

between 23°C and 27°C

Humidity The Humidity is rather low. The average humidity for the dry and wet seasons is 20% and 50%

respectively.

Rainfall The rainfall appears for shorter time, usually two times. During the rainy season, the average rainfall in a

month slightly exceeds 130mm

Radiation The impact of solar radiation is quite high, due to little or no cloud coverage

Towns of the Zone Agordat,, Diredawa,, Kebri, Dar and Awash

Location Dry plateau occupies northern and north-westrn

and the eastern

Topography It is a land with varied geographical

composition. It is a land bisected by rivers and broad valleys,

gorges and steep hills. Its altitude ranges from 1000mts-

2000mts above the sea level.

Vegetation The vegetation comprises tough grass, acacia

forest and thorn scrub

Temperature The yearly average temperature is between

13°C and 28°C. The nights are cooler. The comfort zone is

20°C -25°C .

Humidity The humidity is low. The average highest and lowest are 60% and 35% respectively.

Rainfall The rainfall during the wet season, usually three months, reaches 320mm in a month.

During the dry months, no rainfall appears.

Radiation The radiation impact increases by about 15% more than the impact at sea level.

Towns of the Zone Axum, Mekelle, Gondar, Bahr Dar and Harar.

Location The Humid plateau lies in the western, south and south

western part

Topography The land has varied geographical features and rich

cultivation soil. It has beautiful contrasting scenery. This zone within

the altitude of 1000mts– 2300mts above sea level.

Vegetation It has subtropical, and at lower altitudes, a tropical

vegetation is experienced. Further south, Savanna grassland can be

found with acacia forest

Temperature The average annual temperature is 26°C -13°C . The

comfort zone is between 25°C and 20°C .

Humidity The average annual humidity for the wet and dry season is 80% and

50% respectively.

Rainfall The rainfall is distributed throughout the year, but during the wet season the

monthly average is 310mm. There is at least 25mm of rainfall monthly during the dry

season.

Radiation Due to the altitude, the radiation increases by 15% more than the impacts at sea

level. Towns of the Zone Jimma, Neghelli and Bacco

Location The upland starts from the central part of Ethiopia and

run all along to the north. It forms a pool of high mountains of over

4000meters, at the western, north western, and eastern parts of

the country

Topography This part of the country is called the core of the high

lands. Extensive high plateaus, from which higher mountain groups

stand out, are dissected by small big rivers. It lies above

2300mts from the sea

Vegetation It can support high mountain vegetation, including

coarse grass and giant coniferous forests

Temperature The average annual temperature is 24°C –9°C. the

nights and the earl hours of the day is generally cool. The comfort

in this region lies between 19°C and 24°C

Humidity During the wet season the average is over 80%. But in dry periods it drops to 50%

Rainfall The rainfall is distributed over the year. The average monthly rainfall

Radiation There is an average increase of 20% more in this area than at the sea level

Towns of the Zone Addis ababa, Dessie and DebreMarkos

Location The wet low land holds the extreme western border

of the country

Topography It is generally flat land lying between the plains

of Sudan and the western Ethiopia High lands. This zone is

approximately between the altitudes of 1000mts and 500mts

above the sea level.

Vegetation Broad leaved tropical forest grows in the

highlands and lower river valleys. Its vegetation is

characterized by very tall trees which form a forest canopy.

Temperature The average annual temperature is 33°C-21°C.

Humidity The average maximum humidity is over 70%, and the minimum is about .60%

Rainfall The rainfall is both high and distributed throughout the year. In the wet season, the

monthly average rainfall is about 380mm and during the rest of the year, there is a distributed

monthly rainfall of 75mm

Radiation Due to the fair amount of cloud cover, humidity and vegetation, the extent of the

radiation impact is not very high as in the uplands.

Towns of the Zone Gore, Gambella

Assignment

Choose one of the zones and study the impact of climate on the

• On the design considerations that there are and that need to be made

• Available materials and how they influence building environments

• What are the key characters of that specific zone that make it unique

Submission and presentation will be on the 17th

may 8:30pm