Drought is a persistent problem in many areas, but the basic cause of all droughts is insufficient rainfall. Often this is prolonged over a period of several years. The land can become starved of nourishment or contaminated with mineral salts so that even when it does rain the ground cannot support much growth.

Regular irrigation is necessary for agriculture in those areas where there is not enough rainfall for natural vegetation or crops to thrive. Short term droughts can also be caused when high pressure systems persist over an area of land for several weeks. This blocks the passage of low pressure systems that bring rain. Find out more about dry climates.