Climate change is altering the thermal conditions of Mediterranean cities and territories, and these changes do not affect all parts of the urban territory in the same way. Between the consolidated city and the open countryside lies a broad and heterogeneous space composed of agricultural land, dispersed settlements, infrastructures, residual open spaces, and fragments of ecological systems. Although these territories play an important role in the regulation of local microclimates, planning practice has often treated them as reserves for future urbanization or as spaces lacking a clearly defined role. This research focuses on the peri-urban fringe of Lecce, in the Salento peninsula of Puglia, and investigates the relationship between its ecological and morphological condition and the distribution of thermal vulnerability across the wider urban region.