More than half of the world's population now lives in cities and the proportion is only increasing. As the cities continue to grow, pavement and asphalt became indicators of the intensity of human activities and economic development. As a result, the global impervious surfaces have doubled since the 1980s.

Impervious surfaces are defined as surfaces that prevent surface water from penetrating into the ground. Multiple studies have confirmed that the more we pave, the more we contribute to the creation of urban heat islands and other problems.

80 percent of rainwater falling onto the city's pavement runs off into the rivers instead of the local soil. In a natural environment, only about 20 percent of rainwater flows down into the rivers. Ideally, rainwater would stay where it fell, evaporate, and cool the area. However, the lack of contribution to lowering the microclimate temperature is not the sole issue, as the excessive discharge of rainwater into sewer systems can overwhelm them and contaminate the rivers.

To address the issue, micro-scale urban solutions and practices for reconstruction have begun to emerge. Green roofs, permeable pavement, or rainwater harvesting gardens solve many of the problems outlined above, bringing numerous environmental, social, and economic benefits to cities.

Extensive research has proven that solutions like green roofs can help mitigate the effect of urban heat islands, save energy, reduce noise and urban air pollution, retain water, prevent various particles from polluting the portion of rainwater which runs off, etc. Plants are helpful because they have the ability to use energy from the sun for their biological functions such as photosynthesis, or evaporation, and create a milder microclimate as evapotranspiration cools both the plant foliage and the air around it.

Compared to ordinary black roofs, green roofs provide additional thermal insulation, because of the substrate thickness and the plants help reduce the roof's temperature through evapotranspiration. Energy savings during the cooling season compared to black roofs can reach up to 54 percent in warmer areas but are also effective in cold climates. Apart from reducing water runoff and decreasing the impact on sewerage systems, green roofs also contribute to runoff water quality, decreasing the amount of dust and pollutants that would be sent to the sewer system and the receiving stream.