Google Street View reveals benefits of street trees
FCL researchers developed a method to quantify ecosystem services of street trees. Using nearly 100,000 images from Google Street View, the study helps further understanding on how green spaces contribute to urban sustainability.
Despite the known importance of trees in reducing air temperature by providing shade from the sun’s radiation, we know almost nothing about the actual extent and distribution of shade provided by trees in cities. Using Google Street View, researchers from the Future Cities Laboratory at the Singapore-ETH Centre have developed a method for measuring the shade provided by urban trees over whole cities.
Given the limited resources available to quantify urban ecosystem services in most tropical cities, we need an approach that uses existing datasets, such as those available online, and that provide costeffective assessments at a high spatial resolution over large spatial scales. In this respect, researchers at the Future Cities Laboratory (FCL) found their answer in the huge amount of data that is stored in Google Street View.
Tree-lined streets are a common sight in Singapore, and are very much a trademark of the country, as a part of the national greening strategy. While Google Street View is typically used to obtain panoramic images of city streets from known locations, looking directly upward in Google Street View also provides an image of the sky view, including the canopy of trees in the area.
In this study, the researchers analysed almost 100,000 images extracted from Google Street View, covering over 80% of the street network in Singapore. An algorithm was then applied to each image to quantify the green canopy area. Finally, a model of solar radiation was applied to estimate the amount of shade provided by the tree canopy by quantifying the total amount of solar radiation making it to ground level.
The new method allows the researchers to rapidly estimate how much shade trees are providing across the city. The results show that over 70% of the shade in Singapore’s streets is provided by vegetation. The researchers found that, on average, the tree canopy intercepted 8% of incoming solar radiation. At some locations, the tree canopy intercepted more than 50% of incoming solar radiation.
“The study shows that trees are extremely important in providing shade in Singapore, and this shade could improve thermal comfort for people. Providing trees to help cool the environment is particularly important in tropical cities like Singapore, which suffers heavily from the urban heat island effect,” says Dr Dan Richards, postdoctoral researcher at FCL.
Indeed, Singapore receives an average of 1.8kWh of direct radiation and 3.1kWh of diffuse radiation from the sun. By intercepting solar radiation, trees mitigate the urban heat island effect by reducing the energy stored in concrete and re-radiated during the night.
“In addition to cooling urban microclimates, these trees, which are integrated within dense urban street networks, also provide other ecosystem services,” says Prof Dr Peter Edwards, principal investigator at FCL. “Mapping the provision of ecosystem services by street trees could help city planners to prioritise areas for new planting by identifying streets or street sections with low shading.”
The paper ‘Quantifying street tree regulating ecosystem services using Google Street View’, coauthored by Dr Dan Richards and Prof Dr Peter Edwards, is published in the journal Ecological Indicator Beyond Singapore, this method can be readily applied in other tropical cities and even in temperate cities by collecting Google Street View photographs during summer.