Many new residential blocks are small, and the house, driveway and garage occupy most of the land, leaving very little room for plants. Although earlier subdivided land sizes are bigger, many people have turned the non build-up areas into rock gardens or concreted outdoor area due to busy life style. Rain is not absorbed, and goes down to the drain literally. With fewer plants, absorption of carbon dioxide is reduced, and in the meantime, emission of oxygen is reduced as well.