TOEFL Integrated Writing

📖 Reading Passage

The expansion of urban areas often leads to the loss of natural habitats, but a growing trend in city planning is the creation of green roofs—rooftops covered with vegetation. Proponents argue that green roofs offer significant environmental and economic benefits. First, they mitigate the urban heat island effect. Traditional dark rooftops absorb sunlight and re-radiate heat, raising city temperatures. Green roofs, by contrast, reflect less heat and cool the air through evapotranspiration, potentially lowering ambient temperatures by several degrees. Second, green roofs reduce stormwater runoff. They absorb rainfall, slowing the flow into sewer systems and decreasing the risk of flooding during heavy storms. This can also reduce the burden on municipal water treatment facilities. Third, green roofs extend the lifespan of roofing materials. The vegetation layer protects the underlying membrane from ultraviolet radiation and extreme temperature fluctuations, which are primary causes of roof degradation. Studies suggest that a green roof can last twice as long as a conventional roof, ultimately saving building owners money on replacements.

🎧 Listening Lecture

While the idea of green roofs sounds appealing, the claims made in the reading are overstated and often fail under real-world conditions. Consider the urban heat island effect. Green roofs do cool the immediate surface, but their impact on the overall city temperature is negligible. A single green roof covers a tiny fraction of an urban area, and the cooling effect is localized. To meaningfully lower city-wide temperatures, you would need to cover an impractically large percentage of rooftops. Furthermore, in hot, dry climates, green roofs may actually warm the air because the dark, moist soil can absorb heat during the day and release it at night. Second, regarding stormwater management, green roofs are not a reliable solution. They only absorb light rainfall. During intense storms, which are becoming more frequent due to climate change, the soil quickly becomes saturated, and runoff is almost as high as from a conventional roof. In many cities, the cost of retrofitting existing buildings with the structural reinforcement needed to support the weight of a saturated green roof far exceeds the savings from reduced flooding. Third, the claim about roof longevity is misleading. While a green roof protects the membrane from UV light, the constant moisture and root penetration can damage the roof structure over time. Leaks often develop, requiring expensive repairs. In fact, many case studies show that green roofs need more frequent maintenance and replacement of waterproofing layers than traditional roofs, leading to higher lifecycle costs, not savings.