NATURAL FACTORS AFFECTING SITE PLANNING

CLIMATOLOGY (FACTORS AFFECTING CLIMATE) 

Both weather and climate are characterized by the certain variables known as climatic

factors. They are as follows:

(A) Solar radiation

(B) Ambient temperature

(C) Air humidity

(D) Precipitation

(E) Wind

(F) Sky condition

(A) SOLAR RADIATION

• Solar radiation is the radiant energy received from the sun. 
• It is the intensity of sun rays falling per unit time per unit area and is usually expressed in Watts per square metre (W/m2). 
• The radiation incident on a surface varies from moment to moment depending on its geographic location (latitude and longitude of the place), orientation, season, time of day and atmospheric conditions . 
• It is the most important weather variable that determines whether a place experiences high temperatures or is predominantly cold. 
• The instruments used for measuring of solar radiation are the pyranometer. 
• The duration of sunshine is measured using a sunshine recorder.

(B) AMBIENT TEMPERATURE

• The temperature of air in a shaded (but well ventilated) enclosure is known as the ambient
• It is generally expressed in degree Celsius (ºC).
• Temperature at a given site depends on wind as well as local factors such as shading, presence of water body, sunny condition, etc. 
• When the wind speed is low, local factors strongly influence on temperature of air close to the ground. 
• With higher wind speeds, the temperature of the incoming air is less affected by local factors.
  
  
  
  
  
  
  

(C) AIR HUMIDITY

• Air humidity represents the amount of moisture present in the air, is usually expressed in terms of ‘relative humidity’. 
• Relative humidity is defined as the ratio of the mass of water vapour in a certain volume of moist air at a given temperature, to the mass of water vapour in the same volume of saturated air at the same temperature; it is normally expressed as a percentage.
• It varies considerably, tending to be the highest close to dawn when the air temperature is at its lowest, and decreasing as the air temperature rises.
• The decrease in the relative humidity towards midday tends to be the largest in summer. In areas with high humidity levels, the transmission of solar radiation is reduced because of atmospheric absorption and scattering. 
• High humidity reduces evaporation of water and sweat. Consequently, high humidity accompanied by high ambient temperature causes a lot of discomfort.
  
  
  
  

(D) PRECIPITATION

• Precipitation includes water in all its forms rain, snow, hail or dew. It is usually measured in millimeters (mm) by using a rain gauge. 
• The effects of precipitation on buildings are illustrated in figures.
  
  
  
  

(E) WIND

• Wind is the movement of air due to a difference in atmospheric pressure caused by differential heating of land and water mass on the earth’s surface by solar radiation and rotation of earth. 
• Wind speed can be measured by an anemometer and is usually expressed in metres per second (m/s). 
• It is a major design consideration for architects because it affects indoor comfort conditions by influencing the convective heat exchanges of a building envelope as well as causing air infiltration into the building .
  

(F) SKY CONDITION

• Sky condition generally refers to the extent of cloud cover in the sky or the duration of sunshine. 
• Under clear sky conditions, the intensity of solar radiation increases; whereas it reduces in monsoon due to cloud cover. 
• The re-radiation losses from the external surfaces of buildings increase when facing clear skies than covered skies.