Green roofs, living rooftops with layers of insulation, waterproofing and drainage that support plants, can help cool cities by shading buildings, releasing water vapor and capturing rainfall. Cities such as Chicago and Philadelphia encourage them with zoning incentives and tax credits, and famous examples include the rooftop gardens at Rockefeller Center and the wildflower roof of the California Academy of Sciences in San Francisco. A study of 46 green roofs in the southeastern United States found that nearly half were no longer working as intended, with nine abandoned and twelve removed entirely. Surprisingly, certification and ownership type made little difference. What predicted failure was a change of building ownership, which often brought loss of knowledge and budget cuts. Maintenance can cost from a few cents to more than $3 per square foot each year, and it involves watering, weeding, fertilizing and inspecting drainage. The authors argue that cities should plan long-term maintenance, clear ownership responsibilities and stewardship funding, not just installation grants. Without that care, the benefits that justified the investment can disappear within years.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.