If urban areas experience a significant increase in heat during the summer months, which of the following factors is primarily responsible for this phenomenon in the context of sustainable urban development?

The main cause is the urban heat‑island effect, where city buildings, roads and concrete absorb and re‑emit heat instead of letting it escape. In sustainable urban development, the lack of trees, parks and green roofs means there are fewer surfaces that can cool air through shade or evapotranspiration. Because the heat‑absorbing materials dominate, daytime temperatures rise while nighttime cooling is delayed. For example, a downtown block with only concrete and asphalt will stay much hotter than a nearby park that cools itself with trees and soil. This heat buildup is the primary factor that makes urban summers noticeably hotter.