Calculating cooling extents of green parks using remote sensing: Method and test

• The remote sensing method creates reliable estimates of the areas cooled by isolated green parks.
• The area around a park that benefits from the cooling effect increases with park size.
• Median values of cooling effects beyond park boundaries are between 85 m and 284 m.
• Remotely sensed land surface temperatures correlate closely with those measured on-site.
• The cooling effects of adjacent parks may influence each other, complicating temperature estimation.

A green park can be an effective contributor to the reduction of higher temperatures caused by urban heat island effects. A park's cooling effect extends beyond its boundary into the surrounding streets and buildings. Up to now, the measurement of the extent of the cooling effect beyond the park has relied mainly on on-site observations. An alternative method is to calculate the extent of cooling using remote sensing. The principle of the method is that the cooling effect will decline from the boundary into the surrounding areas to a distance at which the effect is longer felt. Analysis of Landsat TM/ETM+ images of Beijing revealed that cooling effects extend as much as 840 m away from the park in cone case, but as little as 35 m in another. While related in part to park size, the extent of the cooling effect is also influenced by the character of the area around each park. Remote sensing provides a viable alternative to ground temperature measurements, but attention has to be paid to the actual cityscape and characteristics of each park as well as to the resolution of the imagery.