In the past decades, many studies have proposed urban greening as a method to mitigate the rising temperatures in cities and urban heat islands. The cooling effect of urban green spaces can be divided into two components; cooling intensity and cooling extension. These two components are affected by different factors. This paper provides a review of research on the impact of urban greening on temperature and on the parameters that have an effect on that. Based on this review, two categories that have an effect on cooling intensity and
cooling extension were identified: internal factors and external factors. These play an important role in the effectiveness of urban green spaces. As internal factors or indexes, the following were extracted; Size index, Shape index, Vegetation species and Tree canopy coverage are the most common indexes in most of the studies. The external factors can be divided into climate and surrounding properties. A discussion of the reviewed studies reflects the impact of each index on the cooling intensity and cooling extension. The existing methods and techniques for determining these indexes have also been considered in this paper. As such, this study is helpful for designers and planners for decision-making during the design phase.