PDE Q74

Deserts have very low humidity, which means there is insufficient moisture in the air to support the formation of rain. Even if clouds are present, the lack of moisture prevents them from developing into rain-bearing clouds. Additionally, any rain that begins to fall may evaporate before reaching the ground due to the dry conditions.

• A. Maximum air velocity
  Incorrect. High wind speeds can affect cloud movement but do not directly prevent rainfall.

• B. Minimum temperature
  Incorrect. Deserts often have high temperatures; low temperatures are not the limiting factor.

• C. Minimum air velocity
  Incorrect. Wind speed is not the primary reason for lack of rainfall.

• D. Minimum humidity
  Correct. Low atmospheric moisture content is the key reason clouds do not produce rain in deserts.