Diurnal temperature range (DTR) is the difference between the highest and lowest temperatures in a period. It is large in continental and desert climates (15–25 °C) and small in oceanic and humid tropical climates (3–8 °C).
In Spain
The Central Plateau shows diurnal ranges of 15–20 °C in summer, while the Mediterranean and Atlantic coasts rarely exceed 8–10 °C. A large range indicates clear skies and low humidity; a small one indicates cloud cover or proximity to the sea. The urban heat island reduces DTR by keeping minimum temperatures higher.