The average degree of global warming is 1.5°C, which means higher levels of warming. If greenhouse gas emissions increase to a high level, the global warming issue will be more serious. In addition, the urban heat island phenomenon positively affects urban energy consumption and greenhouse gas emissions. However, a simple and accurate calculation process is still lacking to analyse the intensity of the urban heat island (UHI). Therefore, this study proposed an innovative urban heat island calculation workflow to exploit the urban heat island change in city centres. This workflow was built by a 3D computer-aided design tool Rhinoceros with Grasshopper, and a visual programming language running within Rhinoceros. Five steps of the workflow are described. A case study in Osaka, Japan city centre, was conducted to assure the operability of the workflow. The results showed the intensity of the average annual UHI in Osaka city centre was around 0.73°C while the average summer UHI was 0.58°C. However, the summer UHI increased quickly in Osaka city centre, and the intensity is expected to increase to 0.71°C by 2040. The results could provide valuable guidance to local authorities, city planners and policy makers for achieving a more sustainable future in city centres.