Using nearly 100,000 images extracted from Google Street View, a team of researchers has developed a method to map and quantify how street trees regulate ecosystem services.With urban populations exploding in megacities like Tokyo, Shanghai and Delhi to well over 20 million people, it is important to understand how green spaces contribute to urban sustainability, said the researchers from the Future Cities Laboratory at the Singapore-ETH Centre, a research outpost of the Swiss Federal Institute of Technology in Zurich (ETH Zurich). "In addition to cooling urban microclimates, these trees, which are integrated within dense urban street networks, also provide other benefits such as reducing the risk of flash flooding and cleaning the air," explained Peter Edwards, Principal Investigator and Director of the Singapore-ETH Centre.
Trees and plants offer some relief, especially in urban areas with higher ambient temperatures, by providing shade and increasing evaporative cooling.Urban green spaces such as parks, gardens and urban river networks deliver ecosystem services to cities reducing flood risk, cooling urban micro-climates, and creating recreational spaces. To decode this further, the team analysed hemispherical photographs using an algorithm to quantify the proportion of green canopy coverage at 50 metre intervals across more than 80 per cent of Singapore's road network. Google Street View's technology allowed researchers to tap into a standard dataset of panoramic photographs and streetscapes that use a global positioning system (GPS) to map images to specific locations. The high resolution images allowed researchers to estimate the amount of solar radiation that reaches the Earth's surface.
The team found that increasing the cover of the street tree canopy could reduce ground surface and air temperatures on Singapore's streets.In addition, the relative quantity of the canopy may also serve as an indicator of evaporative cooling from leaves and rainfall interception."The study shows that trees are extremely important in providing shade in Singapore and this shade could improve thermal comfort for people," said Dan Richards, a postdoctoral researcher at the Future Cities Laboratory. Since Google Street View covers many of the world's cities, the method could be readily applied to quantify the proportion of canopy coverage and solar radiation in other tropical cities. If Google Street View images were collected during the growing season, the method may also be adapted to assess cities in temperate zones that experience a seasonal loss of tree leaves, the team noted in a paper appeared in the journal Ecological Indicators.