Abstract-Climate change is one of the main concerns of our times, and it became even more noticeable due to its impact on global temperature, precipitation patterns, and even arctic sea ice melting. Moreover, it has been proven that climate change is one of the main factors affecting the Urban Heat Island (UHI); which in its turn, increases the energy demand in sustainable cities, where reducing power costs still a major challenge. Furthermore, in order to keep a balanced environment, and contribute to temperature mitigation, the use of vegetation cover is definitely one remarkable strategy. It helps decreasing the temperature down to the values required in sustainable development, reducing energy consumption, and lowering Greenhouse Emission (GHE). In this work, we assess the impact of green-roofs on UHI, and we try to define a decision model that helps calculating the best green-roof/green-infrastructure ratio. Besides, we aim to identify the best practices and measures to take in order to mitigate the UHI in semi-arid climate areas.Our work involves the use of a Geographic Information System (GIS), which provides a support to estimate the greenery conditions. Our methodology is based on a probabilistic and comparative approach, and evaluated using different green-roof models. We select a residential area in Constantine, Algeria as our study subject, and we use ENVI-met as the software support. Among the findings of this study, providing proper, yet experimentally proven recommendations on how, how much and where to use green roofs, was our main contribution. In addition, the results of our study indicate not only the impact of green-roofs on UHI, but also the effect of large-scale green-roof installation on the liveable areas in sustainable cities.Index Terms-Climate change, geographic information system, green-roofs, sustainable development, urban heat island.