How can precast concrete reduce the heat-island effect described in the LEED Sustainable Sites credit (SSc7.1)?

Sustainable Sites credit 7.1 is intended to reduce heat islands, meaning the thermal gradient difference between developed and undeveloped areas. The heat-island effect is partially attributed to the dark surfaces of roofing and paving, and the additional heat in developed areas increases HVAC loads and contributes to the creation of smog. Reducing heat islands minimizes impact on microclimate and human and wildlife habitat. Precast concrete parking structures that place at least 50% of the spaces under cover (for example, underground, under a building, or under a deck or roof) can reduce this effect. Any roof used to shade or cover parking must have a solar reflective index (SRI or albedo) of at least 29. In addition, high-albedo vertical precast concrete wall surfaces reduce the heat-island effect.  more