City as a Resource
What if, in the future, people prefer to live closer to nature, and the cities are repurposed. Old buildings and dense cities are converted into resource collectors, solar energy collection, wind collection, and water collection. Trees can be planted in old brick and concrete buildings, to be able to be studied and monitored as they grow. Once the trees are big enough to over take the building, getting water from the underground cisterns.
Open spaces will be porous, and connected to these new underground cisterns, where rainwater and melted snow can be collected. This water will be used by the trees and plants growing in the repurposed buildings.