The architectural configuration and urban development of cities have a considerable influence on the mitigation of overheating and the formation of urban heat islands. Integrating natural elements into urban landscapes offers a convincing solution for mitigating the effects of urban heat islands, while facilitating better management of the water cycle and improving inter-urban aesthetics. The purpose of this work is to investigate the way in which optimal control techniques can be used to design green spaces and deal with the mathematical environmental problems associated with the urban heat island that affects cities. A porous media based thermal model (Navier-Stokes-Forschheimer-Fourier system) is formulated for the assessment of urban heat island mitigation. The emphasis was on outlining the feasibility and relevance of a better combination of optimisation techniques and the optimal control theory of partial differential equations to ensure thermal comfort within urban spaces. To evaluate the methodology, we adopt a numerical scheme with a finite element method, the projected spectral gradient algorithm, and rely on the free software FreeFem++. The effectiveness and robustness of the approach are assessed on the basis of the quality of the results obtained with a realistic model.