Classification, causes and impacts of drought

DROUGHT

Drought is a weather-related natural disaster. It affects vast regions for months or years. It has an impact on food production and it reduces life expectancy and the economic performance of large regions or entire countries.
Drought is a recurrent feature of the climate. It occurs in virtually all climatic zones, and its characteristics vary significantly among regions. Drought differs from aridity in that drought is temporary; aridity is a permanent characteristic of regions with low rainfall.
Drought is a gradual hazard of nature that has a cumulative effect. It is related to a deficiency of precipitation over an extended period of time, usually for a season or more. This deficiency results in a water shortage for some activity, group, or environmental sector. Drought is also related to the timing of precipitation. Other climatic factors such as high temperature, high wind, and low relative humidity are often associated with drought.

Drought may be defined conceptually or operationally.
Conceptually, drought may be defined as a protracted period of deficient precipitation that causes extensive damage to crops, resulting in loss of yield.
Operational definition of drought helps to identify the beginning, end and degree of severity. In this case, the beginning of drought is identified by considering the degree of departure from the precipitation average over a specified time period. Usually, a historical average is considered as a threshold to identify the beginning of the drought. Operational definitions are used to analyze drought frequency, severity, and duration for a given historical period. A climatology of drought for a given region provides a greater understanding of its characteristics and the probability of recurrence at various levels of severity. Information of this type is beneficial in the formulation of mitigation strategies.

Types of drought

1. Meteorological drought: Meteorological drought is defined on the basis of the degree of dryness, in comparison to a normal or average amount, and the duration of the dry period. Definitions of meteorological drought must be region-specific, since the atmospheric conditions that result in deficiencies of precipitation are highly region-specific. Data sets required to assess meteorological drought are daily rainfall information, temperature, humidity, wind velocity and pressure, and evaporation.
2. Agricultural drought: Agricultural drought links various characteristics of meteorological drought to agricultural impacts, focusing on precipitation shortages, differences between actual and potential evapo-transpiration, soil-water deficits, reduced groundwater or reservoir levels, and so on. Plant water demand depends on prevailing weather conditions, biological characteristics of the specific plant, its stage of growth, and the physical and biological properties of the soil. A good definition of agricultural drought should account for the susceptibility of crops during different stages of crop development. Deficient topsoil moisture at planting may hinder germination, leading to low plant populations per hectare and a reduction of yield. Data sets required to assess agricultural drought are soil texture, fertility and soil moisture, crop type and area, crop water requirements, pests and climate.
3. Hydrological drought: Hydrological drought refers to a persistently low discharge and/or volume of water in streams and reservoirs, lasting months or years. Hydrological drought is a natural phenomenon, but it may be exacerbated by human activities. Hydrological droughts are usually related to meteorological droughts, and their recurrence interval varies accordingly. Changes in land use and land degradation can affect the magnitude and frequency of hydrological droughts.Data sets required to assess hydrological drought are surface-water area and volume, surface runoff, streamflow measurements, infiltration, water-table fluctuations, and aquifer parameters.
4. Socioeconomic drought: Socioeconomic definitions of drought associate the supply and demand of some economic good with elements of meteorological, hydrological, and agricultural drought. It differs from the other types of drought in the sense that its occurrence depends on the processes of supply and demand. The supply of many economic goods, such as water, forage, food grains, fish, and hydroelectric power, depends on the weather. Due to the natural variability of climate, water supply is ample in some years, but insufficient to meet human and environmental needs in other years.   Socioeconomic drought occurs when the demand for an economic good exceeds the supply as a result of a weather-related shortfall in water supply.Data sets required to assess socioeconomic drought are human and animal population and growth rate, water and fodder requirements, severity of crop failure, and industry type and water requirements

 Causes of drought

1. Land and water temperatures cause drought. As overall temperatures increase more water evaporates and severe weather conditions increase. Landscapes and crops need more water to survive and overall the demand for water increases.
2. Air circulation and weather patterns also cause drought. Key events like     El-Nino or La-Nina help contribute to drought in areas
3. Soil moisture levels also contribute to drought. When soil moisture is depleted there is less evaporation of water to create clouds. Surface temperatures rise, more water is needed and less is available which contributes to a more severe drought.
4. Drought can also be a supply and demand of water issue. When a region is growing rapidly the demand for water can exceed the supply. When weather conditions, temperatures or air patterns push a region toward a drought the demand for water by people can offset or worsen the situation depending on how the region reacts. Excessive irrigation contributes to a drought. 
5. If the timing of water doesn’t match the agricultural season there may be too much water when it is not needed it and too little when it is actually needed. Proper storage and collection of water is key to counter balancing this cycle and clearly in the scope of human management.

Impact of drought
Drought produces a complex web of impacts that spans many sectors of the economy and extends beyond the area experiencing physical drought. This complexity exists because water is integral to society's ability to produce goods and provide services.
Impacts are commonly referred to as direct and indirect.
Direct impacts include:

1. reduced crop, range land, and forest productivity, 
2. increased fire hazard
3. reduced water levels
4. increased livestock and wildlife mortality rates and 
5. damage to wildlife and fish habitat.

The direct impacts influence:

1. crop productivity
2.  income for farmers and agribusiness
3. prices for food and timber
4. unemployment
5. exemption to farmers who borrowed heavily from banks
6. migration

Types of drought impacts are:

1. Economic impacts: The economic impacts of drought are listed below:

1. Droughts destroy growth of crops resulting in poor yields and poor quality crops. Excessive funds are used to provide sufficient water to crops
2. Death of livestock due to lack of food and water
3. Reduced timber production due to wild fires, low productivity of forest land and  and loss of young trees.
4. Loss of fishery production due to damaged fish habitat due to drought.
5. Loss of recreation and tourism
6. Loss to industries manufacturing farm equipment.
7. Loss to hydroelectric power generating companies
8. Loss of revenue to water supply companies
9. Loss to inland river navigation based transport companies
10. Increased cost due to import of food.

      2. Environmental impacts: The environmental impacts of drought are listed below:

1. Environmental impact includes forest fires, soil erosion, damage to life forms and their habitat coupled with decline in air and water quality.
2. Wildlife may migrate to other areas.
3. Increased stress to endangered species
4. Decrease in water level in reservoirs, ponds, lakes and loss of wetlands
5. Dry top soil becomes prone to erosion by wind leading to reduced soil quality and low biological productivity of landscape.
6. Loss of biodiversity and extinction of species

      3.Social impacts: The social impacts of drought are listed below:

1. Disputes due to water shortage and lifestyle changes
2. Revenue loss due to drought causes physical, mental stresses that contribute to loss of human lives due to suicidal tendencies
3. Reduction in recreational activities
4. Mass migration of communities
5. Reduced fire fighting ability
6. Sustenance on basic food leading to malnutrition and high infant mortality rate
7. Steeply declining quality of life in the affected community