heat islands urban heat islands air pollution and control global effects of air pollution

1. Urban Heat Islands
Ravi Kumar GARRE

2. Heat Islands
• Heat island is an urban area (or) metropolitan
area that is significantly warmer than its
surrounding rural areas. Heat islands also termed
as urban heat island (UHI).
• The difference is usually larger at night during the
day, and is most apparent when winds are weak.
• The air in an urban heat islands can be as much
as 11˚C higher than rural areas surrounding the
city.

3. Urban Heat Island

6. Causes for UHI
• The main cause off UHI is from the modification
of land surfaces. Waste heat generated by energy
usage is a second most contributor.
• Dark materials and concrete absorbs solar energy
and release it back the surrounding air as heat.
This contribution causes the temperature in
urban areas to be much better than rural areas.
• As population centres grow they tend to modify a
greater and greater area of land and have a
corresponding increase in average temperature.

7. Causes for UHI
• Especially for that night time warming, the
principal reason is buildings block surface heat
from radiating into the relatively cold night sky
thermal properties of surface materials, and
lack of evapotranspiration in urban areas.
• The tall buildings with in urban areas provide
multiple surfaces for the reflection and
absorption of sun light, increasing the
efficiency with which urban areas are heated.

8. Causes for UHI
• Waste heat from automobiles, air
conditioning, industry and other sources also
contributes to UHI.
• High levels of pollution in urban areas can also
leads to UHI, as many forms of pollution
change the radioactive properties of the
atmosphere.

10. Effects of UHI
• The buildings (congested/tall), blocks the wind
and become effective heat traps for solar
radiation. This results in number of socio-
economic-environmental effects such as greater
energy usage (power consumption), potential
water shortage and high mortality rates.
• Due to the large heat, the UHIs will receive less
precipitation than surroundings. This leads to
increase in water demand, reduced rainfall.

11. Effects of UHI
• Due to impervious surfaces the UHI can modify
urban air and water resources. Reduces the
dissolved oxygen in streams and makes aquatic
life harder.
• Reduces the urban vegetation, ecological
productivity and interrupt atmospheric carbon
cycling.
• Increased temperatures lead to formation of
ozone and also contribute to worsened air
quality.

12. Effects of UHI
• Due to concrete surfaces and pavements, the
infiltration will be zero. So, the ground water
quantities will be reduced.
• Due to usage of A.C.s and refrigerators, the
concentration fo greenhouse gases will be
increased in UHIs. This leads to global
warming.

13. UHI mitigation
• Increasing trees and vegetative cover
• Installing green roofs (roof top gardens, Eco
roofs, etc.)
• Using cool roofs/ cool pavements

14. UHI mitigation
Trees and vegetation
• Trees and other plants help to cool the
environment.
• It is an effective way to reduce urban heat
islands.
• Trees also reduce air pollution, higher demand
on cooling systems the problems related to
heat and pollution.

15. UHI mitigation
Green roofs
• Green roof provide shade and remove heat
from the air through evapotranspiration.
• Reduces temperatures on the roof and
surrounding air as well as inside of rooms.
• On hot summer days the surface temperature
of a green roof can be cooler than the air
temperature.

16. UHI mitigation
Cool roofs
• Painting roof tops with white is best strategy
to reduce UHI effect. White roof tops allow
high solar reflectance.
• The roofs made up with slate, terracota, dutch
seam panels, advanta shingle, etc. will act as
cool roofs and reduces the effects of UHI.

17. Thank you