Downdraught Effect

• India’s metropolitan cities are replete with:
  • High compound walls.
  • Podiums.
  • High-rise buildings of varying heights.
• These are often clumped together without adequate spacing, affecting the wind’s speed — rougher surfaces have a greater slowing effect — and direction.
• When a wind’s flow is interrupted by tall buildings, it can instead be funnelled through narrow spaces, where it accelerates and builds up into a gust before reaching the pedestrians walking around the buildings.
• This phenomenon is called the Venturi effect and has been observed in London and Jaipur, among other cities.
• When winds slam into high-rise buildings, they can be forced downwards along the structures in a phenomenon called the downdraught effect, which further pushes the wind lower down into stronger gusts.

Prelims Question

Q. Consider the following statements regarding the Downdraught Effect:

1. It occurs when winds hitting high-rise buildings are forced downwards along the structures.
2. It can push wind towards the lower levels of buildings into stronger gusts.
3. It is the phenomenon in which wind accelerates while passing through narrow spaces.

Which of the statements given above is/are correct?

(a) 1 and 2 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3

Answer: (a) 1 and 2 only

• Statement 3 describes the Venturi effect, not the Downdraught effect.