Why do deserts sometimes get very cold at night even after scorching days?

Deserts often have low humidity, and water vapour is one of the main gases that slows heat loss from the ground. When skies are clear, the surface radiates heat directly into space more efficiently than under cloudy conditions. Because there is also little vegetation or water to store heat, daytime warmth does not linger for long. That is why many deserts have large day-night temperature swings, sometimes more than 20°C or 30°C in a single day.