Types of Drought
1. Based on Duration
a) Permanent drought - This is characteristic of the desert climate where sparse vegetation grows. It is adapted to drought and agriculture is possible only by irrigation during the entire crop season.
b) Seasonal drought - Found in climates with well-defined rainy and dry seasons. Most of the arid and semiarid zones fall in this category. The duration of the crop varieties and planting dates should be such that the growing season falls within the rainy season.
c) Contingent drought - Involves an abnormal failure of rainfall. It may occur almost anywhere, especially in most parts of humid or sub-humid climates. It is usually brief, irregular, and generally affects only a small area.
d) Invisible drought - Can occur even when there is frequent rain in an area. When rainfall is inadequate to meet the evapotranspiration losses, the result is borderline water deficiency in soil resulting in less than the optimum yield. This occurs usually in humid regions.
2. Based on Nature of the Users (NCA, 1976)
a) Meteorological drought - Defined as a condition where the annual precipitation is less than the normal over an area for a prolonged period (month, season, or year).
b) Atmospheric drought - Due to low air humidity, frequently accompanied by hot dry winds. It may occur even under conditions of adequate available soil moisture. Plants show wilting symptoms during the hot part of the day when transpiration exceeds absorption temporarily for a short period. When it decreases, absorption keeps pace with transpiration and plants revive (mid-day wilt).
c) Hydrological drought - Prolonged meteorological drought results in hydrological drought with depletion of surface water and consequent drying of reservoirs, tanks, etc. It results in a deficiency of water for all sectors using water. This is based on water balance and how it affects irrigation as a whole for bringing crops to maturity.
d) Agricultural drought - Result of soil moisture stress due to imbalance between available soil moisture and evapotranspiration of a crop. It is usually gradual and progressive. Plants can therefore adjust at least partly to the increased soil moisture stress. This situation arises as a consequence of scanty precipitation or its uneven distribution both in space and time. It is also usually referred to as soil drought.
