Indeed the protection of the ground surface by a layer of gravels from the solar rays makes it possible to cool the soil
while allowing evaporation. In arid regions, the difference between the maximum temperatures of the outside ambient air and the cooled temperature of the earth at a depth of one meter may attain 15°C in mid-summer season 3.
The temperature of the ground surface is characterized by broad diurnal and annual variations, which are determined
by the absorbed solar energy and the temperature of the ambient air. The range of daily surface temperature is
usually larger in summer, especially in arid regions, when the solar radiation impinging on the surface is higher. It is
shorter in winter, mainly in cold regions.