Urban Atmosphere

Urban Heat Island (UHI):
The urban heat island effect refers to the increased temperature in urban areas compared to their rural surroundings. This effect is mainly caused by the concentration of buildings, roads, and other human activities, which absorb and retain heat, increasing local temperatures. Explanation of Statements:
(A) Urban heat island can exacerbate urban flooding by intensifying rainfall intensity.
This is correct because the increased temperatures in urban areas can cause more intense storms and rainfall, thus exacerbating the risk of flooding.
(B) Urban canyons increase ventilation by trapping heat and thus enhancing urban heat island effect.
This is incorrect because urban canyons (narrow spaces between tall buildings) typically reduce ventilation, leading to more heat being trapped, which intensifies the urban heat island effect.
(C) Program evaluation and review technique (PERT) is always used to estimate the economic impact of mitigation strategies for urban heat island effect.
This is incorrect because PERT is a project management tool used for scheduling, not directly for estimating economic impacts of environmental strategies.
(D) In general, land surfaces in urban areas emit more long wave radiation compared to those in rural areas, and thus contribute to higher night time temperature.
This is correct because urban areas, with their concrete and asphalt, absorb and emit more long-wave radiation during the night, keeping temperatures higher.
Thus, the correct answers are (A) and (D).