Sweet Potatoes beat Green Roofs at Sinking Heat Islands

In hot weather there is nothing like green roofs to help reduce the heat island effect, except perhaps this experiment by NTT Development in Japan. They planted a hydroponic garden of sweet potatoes because they evidently control the rise in heat by expanding their leaves and evaporating a large amount of water. If we read the translation correctly, the sweet potatoes were about 1.5 times as effective as a green roof at reducing the heat island effect . Of course it takes energy and equipment to run all of these hydroponics. Why not just grow sweet potatoes in a green roof and get the best of both worlds?::Japan for Sustainability and ::Garbagenews