Reading: True / False / Not Given: Question 2

The urban heat island effect describes the tendency of cities to register significantly higher air temperatures than the rural areas that surround them, a difference that can exceed seven degrees Celsius during still, clear nights in large metropolitan areas. Several interacting factors are responsible for this phenomenon. Dark, impervious surfaces such as asphalt roads and roofing materials absorb a much greater proportion of incoming solar radiation than vegetated or unpaved ground, and because these materials also have a high thermal mass, they release this stored heat slowly after sunset, keeping nearby air warmer well into the night. At the same time, the removal of trees and other vegetation during urban development eliminates a natural cooling process known as evapotranspiration, in which plants release water vapour that absorbs heat from the surrounding air as it evaporates.

The dense arrangement of tall buildings compounds these effects by altering airflow: narrow streets flanked by high walls trap warm air and reduce the wind speeds that would otherwise disperse it, while the vertical surfaces of buildings reflect additional solar radiation back and forth between structures rather than allowing it to escape upward. Waste heat released directly by vehicles, industrial processes and air conditioning units, though a comparatively minor contributor in most cities, adds a further, constant source of warming that has no rural equivalent.

City planners in a number of countries have begun testing methods intended to counter the effect, including the installation of reflective "cool roofs" that are coated with light-coloured materials to reduce solar absorption, and the expansion of urban tree canopy along streets and in newly designed public parks. Early results from several pilot schemes indicate that surface temperatures on treated rooftops can fall noticeably compared with untreated roofs nearby, though researchers caution that citywide temperature reductions depend on how widely such measures are adopted and are difficult to measure precisely across an entire urban area, since air temperature is also affected by unrelated factors such as regional weather patterns and background climate trends that vary from year to year.

Do the following statements agree with the information given in the passage? Write TRUE, FALSE or NOT GIVEN.

1. Cities can be more than seven degrees Celsius warmer than surrounding rural areas on some nights.
2. Vegetated ground absorbs more solar radiation than dark, paved surfaces such as asphalt.
3. Evapotranspiration is a natural process that cools the air as plants release water vapour.
4. Narrow streets between tall buildings tend to increase wind speeds, helping disperse warm air.
5. Waste heat from vehicles and air conditioning is, in most cities, the single largest contributor to the urban heat island effect.
6. Cool roofs are coated with light-coloured materials to reflect more sunlight.
7. Cool roofs cost more to install than standard dark roofing materials.
8. The urban heat island effect was first documented in the twentieth century.