The diurnal temperature range (DTR) is the difference between the maximum (typically mid-afternoon) and minimum (typically around sunrise) temperatures in a single day. It is a fundamental climate variable that reflects the balance between daytime solar heating and nighttime radiative cooling, modulated by cloud cover, humidity, wind, altitude, and distance from the coast.
Large DTR (15–25 °C or more) is characteristic of arid, continental, and high-altitude environments where clear skies allow strong daytime heating and rapid nighttime cooling: interior Spain, the Sahara, central Asia, and high deserts. Small DTR (2–5 °C) is typical of marine, coastal, and cloudy environments where the ocean moderates temperature extremes and cloud cover limits both daytime heating and nighttime cooling: the Canary Islands, the UK, and tropical oceanic islands.
The DTR has practical importance for agriculture (frost risk increases with large DTR), human comfort and health (large DTR with warm days and cold nights requires adapting clothing and heating), and energy demand (large DTR means greater heating and cooling requirements). Interestingly, DTR has been decreasing globally over recent decades as climate change causes minimum temperatures to rise faster than maximum temperatures — nights are warming more than days. In Spain, the meseta regions (Madrid, Castilla y León, Castilla-La Mancha) are famous for extreme DTR — the saying "nueve meses de invierno y tres de infierno" captures the seasonal extremes, while daily ranges of 15–20 °C are common in summer.