"Green Roofs" are rooftops designed to help manage rainwater in cities by holding onto some of it and letting it evaporate slowly. They can be a good way to deal with stormwater runoff in urban areas. In cold places, green roofs might not work as well because the water doesn't evaporate easily. Early green roofs didn't always help with water quality because they released nutrients into the environment. To keep green roofs working well, they need regular care to keep the plants healthy and prevent clogs in the drainage system. Some green roofs are also being used to grow food, making them even more beneficial.