There are four types of drought based on agricultural criteria. They are:
  • Permanent drought
    There is a constant excess of evapotranspiration over precipitation. Vegetation is limited to desert dwelling plants causing agriculture to be impossible.
  • Seasonal drought
    This type of drought only occurs at the margins of great deserts where there are arid conditions for most of the year. Agriculture here is only successful during the wet seasons.
  • Contingent drought
    Contingent droughts are experienced in areas that normally have enough moisture. Problems arise in these regions from poor framing and irrigation.
  • Invisible drought
    There are no physical changes to the landscape from this drought even though evaporation and transpiration exceed precipitation. Vegetation lacks the moisture required for optimum growth. The potential agricultural yield of the land is reduces, but this problem is easily dealt with by the used of irrigation.