Drought and it's classification in a simplified way
- 1. Drought and it types
- 2. Introduction • Low rainfall or failure of monsoon rains is a recurring feature in India. • This has been responsible for droughts and famines. The word drought, generally, denotes scarcity of water in a region. • Though, aridity and drought are due to insufficient water, aridity is a permanent climatic feature and is the culmination of a number of long-term processes. • However, drought is a temporary condition that occurs for a short period due to deficient precipitation for vegetation, river flow, water supply and human consumption. • Drought is due to anomaly in atmospheric circulation.
- 4. DEFINITION OF DROUGHT • Drought is a climatic anomaly, characterised by deficient supply of moisture resulting either from • sub-normal rainfall, • its erratic distribution, • higher water requirement • or a combination of all these factors. • There is no universally accepted definition of drought. • Early workers defined drought as prolonged period without rainfall. • According to Ramdas (1960) drought is a situation when the actual seasonal rainfall is deficient by more than twice the mean deviation. • American Meteorological Society defined drought as a period of abnormally dry weather sufficiently prolonged for lack of water to cause severe hydrological imbalance in the area affected. • It is the result of imbalance between soil moisture and evapotranspiration needs of an area over a fairly long period as to cause damage to standing crops and to reduce the yields.
- 5. CONCEPT OF DROUGHT • Conceptually, drought is considered to describe a situation of limited rainfall that is substantially below what has been established to be a "normal" value for the area concerned. • The concept of drought varies from one region to another depending upon – normal climatic conditions, – available water resources, – agricultural practices – and various socio- economic activities of the region. • Risk involved in successful cultivation of crops depends on – the nature of drought (chronic and contingent), – its probable duration and periodicity of occurrence within the season. • In the arid region where the mean annual rainfall is less than 500 mm, drought is almost an inevitable phenomenon in most of the years. • In semi-arid regions (mean annual rainfall 500-750 mm), drought occur in 40 to 60 per cent of the years due to deficit seasonal rainfall or inadequate soil moisture availability between two successive rainfall events. • Even in dry sub-humid regions (annual rainfall 750-1200 mm), contingent drought situations occur due to break in monsoon conditions.
- 6. DROUGHTS IN INDIA 68 % of area is vulnerable on account of low to medium rainfall Out of 141 m ha net sown area, only 40% is irrigated Between 1871-2012, India witnessed 23 major droughts and 6 of them were severe 32% area has drought frequency less than three years The 2002 drought is severest in last 130 years, affected 56% area and livelihood of 300 million people in 18 States
- 8. Terms used for deficit rain • Dry spell: Rainless period for short time (i.e., >10 days in light soils, >15 days in heavy soils). The interval between the end of a seven day wet spell, beginning with the onset of effective monsoon and another rainy day with 5 e mm of rain (where “e” is the average daily evaporation). • Drought: Prolonged dryspell resulting in wilting or drying of crops. • Famine: Severe form of drought called as famine. •
- 9. Classification of drought • Drought can be classified based on • Impact • duration, • nature of users, • time of occurrence • and using some specific terms.
- 10. Based on Impact or relevance to users – Meteorological drought – Atmospheric drought – Hydrological drought – Agricultural drought (soil drought)
- 11. Meteorological drought • Meteorological drought is defined as a condition, where the annual precipitation is less than the normal over an area for prolonged period (month, season or year). • As per precipitation, the below normal departure of rainfall was classified by the IMD, India, as – mild (1- 25%) – moderate (26 – 50%) – and severe (above 50%). • This is also a period of abnormally dry weather which is as per spatial extent sufficiently prolonged. • Droughts are considered as large scale (up to 25% area is affected) and worst (from 26 to 50% area affected).
- 12. Meteorological drought (contd…) • Variety of meteorological definitions in different countries illustrates why it is not possible to apply a definition of drought developed in one part of the world to another. • For instance, the following definitions of drought have been reported: – United States (1942): Less than 2.5 mm of rainfall in 48 hours, – Great Britain (1936): Fifteen consecutive days with daily precipitation less than 0.25 mm, – Libya (1964): When annual rainfall is less than 180 mm, and – Bali (1964): A period of six days without rain. • .
- 13. Atmospheric drought • Atmospheric drought is due to low air humidity, frequently accompanied by hot dry winds. • It may occur even under conditions of adequate available soil moisture. • It refers to a condition when plants show wilting symptoms during the hot part of the day when transpiration exceeds absorption temporarily for a short period. • When absorption keeps pace with transpiration the plants revive. (Midday depression or incipient wilting).
- 14. Hydrological drought • Meteorological drought, when prolonged results in hydrological drought with depletion of surface water and consequent drying of reservoirs, tanks etc. • It is best defined as deficiencies in surface and sub-surface water supplies leading to a lack of water for normal and specific needs. • Such conditions arise, even in times of average (or above average) precipitation when increased usage of water diminishes the reserves. • This is based on water balance and how it affects irrigation as a whole for bringing crops to maturity
- 15. Agricultural drought (soil drought): • It usually triggered by meteorological and hydrological droughts, occurs when soil moisture are inadequate during crop growing season causing crop stress and wilting. • Plant water demand depends on prevailing weather conditions, biological characteristics of the specific plant, its stage of growth and physical and biological properties of the soil. • Agricultural drought thus arises from variable susceptibility of crops during different stages of crop development, from emergence to maturity. • In India, it is defined as a – period of four consecutive weeks (of severe meteorological drought) with a rainfall deficiency of more than 50 per cent of the long-term average LTA) – or with a weekly rainfall total of (WRT) of 5 cm or less from mid-May to mid- October (khan") when 80 per cent of India's total crop is planted – or six such consecutive weeks during the rest of the year
- 16. Classification of Agricultural Drought • seven major types ( in dryland areas) : • Early season drought: The early season drought occurs due to delay in commencement of sowing rains. Farmers sow the seed by taking advantage of early rains. A long dry spell may lead to withering of seedlings and poor crop establishment. • Mid season drought: This occurs in association with long gaps between two successive rain events, if moisture stored in the soil falls short of water requirement of crop during vegetative stage. • On other occasions the mid season drought may be associated with low and inadequate rainfall in the growing season to meet the crop water needs as per the phenological stage. • Late season or terminal drought: If the crop encounters moisture stress during the reproductive stage due to early cessation of rainy season and rise in temperature the situation hastens the process of maturity
- 17. Classification of Agricultural Drought (Contd..) Chronic Drought • It is common in arid areas where rainfall and stored soil moisture are inadequate to meet crop water requirement during most of the years. • Here, the assured growing period is hardly 6 to 7 weeks. • These are characterised as chronic drought or highly thought prone areas. Apparent Drought • This condition is observed in low to medium rainfall regions due to mismatching of the cropping pattern in relation to rainfall/moisture availability. Contingent Drought • This 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. Invisible Drought • This 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 optimum yield. This occurs usually in humid regions.
- 18. CAUSES OF AGRICULTURAL DROUGHT • Changing weather patterns manifested through the excessive build up of heat on the earth's surface, • Meteorological changes that result in a reduction of rainfall, • Reduced cloud cover that results in greater evaporation rates, • Over-grazing and poor cropping methods that result in reduced water retentive capacity of the soil, and • Improper soil conservation techniques that leads to soil degradation. • Atmospheric conditions such as climate change, ocean temperatures, changes in the jet stream and changes in the local landscape are all culprits in the long story of the causes of droughts.
- 19. Natural and Social Dimensions of Drought Meteorological Agricultural Hydrological Socio-economic Decreasing emphasis on the natural event (precipitation deficiencies) Increasing complexity of impacts and conflicts Time/Duration of the event Increasing emphasis on water/natural resource management
- 20. Classification of drought Based on duration • Permanent drought: This is characteristic of the desert climate where sparse vegetation growing is adapted to drought and agriculture is possible only by irrigation during entire crop season. • Seasonal drought: This is found in climates with well defined rainy and dry seasons. Most of the arid and semiarid zones fall in this category. Duration of the crop varieties and planting dates should be such that the growing season should fall within rainy season. • Contingent drought: This 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. • Invisible drought: This can occur even when there is frequent rain in an area. When rainfall is inadequate to meet the evapo-transpiration losses, the result is borderline water deficiency in soil resulting in less than optimum yield. This occurs usually in humid regions.
- 21. Classification based on aridity index • Besides rainfall, various other climatic and soil factors have also been used for drought classification. • These include the aridity index (la) anomaly and ratio of actual to potential evapotranspiration (AE/PE). • Studies at CAZRI categorised drought based on moisture stress during crop growing season using the following criteria: • Drought free period: When cumulative AE curve is above cumulative PE/2 curve, • Moderate drought period: When cumulative AE curve lies between cumulative PE/2 and PE/4 curves, and • Severe drought period: When cumulative AE curve is below cumulative PE/4 curve.
- 22. Classification of grought based on AE/PE AE/PE (%) during different phenophases Drought Intensity Seedling Vegetative Reproductive 76-100 Nil S0 V0 R0 51-75 Mild S1 V1 R1 26-50 Moderate S1 V2 R2 25 or less Severe S2 V3 R3
- 23. Other terms to describe drought Relative/ Apparent drought: • The drought for one crop may not be a drought situation for another crop. This is due to mismatch between soil moisture condition and crop selection • For Eg. A condition may be a drought situation for growing rice, but the same situation may not be a drought for growing Pulses like green gram and black gram. Physiological drought: • It Refers to a condition where crops are unable to absorb water from soil even when water is available, due to the high osmotic pressure of soil solution due to increased soil concentration, as in saline and alkaline soils. • It is not due to deficit of water supply.
- 24. CRITERIA OF DROUGHT • National Commission on Agriculture (1976) considered agricultural drought as an occasion • when at least four consecutive weeks receive rainfall half of the normal (normal rainfall being 5 mm or more) during the crop season (mid-May to mid-October) • or six such weeks during other period.
- 25. CRITERIA OF DROUGHT • The criteria adopted in different states also vary depending on the rainfall and crops grown in the region • Tamil Nadu - less than 900 mm rainfall • Karnataka considers – less than 400 mm during kharif and – less than 30 per cent during crop season – and 20 per cent deficiency of rainfall during crucial stages of crop growth • Rajasthan -when the productivity decrease by 50 per cent compared to a good crop year. • Many of the states also follow the "Annawary" system wherein the crop conditions are assessed through visual estimates • The criterion followed is: • Production above 75 per cent of normal: No drought, • Production 50 to 75 per cent of normal: Moderate drought, • Production 25 to 50 per cent of normal: Severe drought, and • Production less than 25 per cent normal: Disastrous drought.
- 26. State-wise number of districts, blocks and area covered under DPAP in India as in 2007 • Name of the state No. of district • Andhra Pradesh 11 • Bihar 6 • Chhattisgarh 8 • Gujarat 14 • Himachal Pradesh 3 • Jammu & Kashmir 2 • Jharkhand 15 • Karnataka 15 • Madhya Pradesh 24 • Maharashtra 25 • Odisha 8 • Rajasthan 11 • Tamil Nadu 17 • Uttarakhand 7 • Uttar Pradesh 15 • West Bengal 4 • India 185 No of blocks Are in sq.km 94 99218 30 9533 29 21801 67 43938 10 3319 22 14705 100 34843 81 84332 105 89101 149 194473 47 26178 32 31969 80 29416 30 157% 60 35698 36 11594 972 745914
- 27. Administrative districts frequently affected by drought in India. State Andhra Pradesh Bihar Gujarat Haryana Jammu & Kashmir Karnataka Madhya Pradesh Maharashtra Orissa • Districts • Anantapur, Chittoor, Kadapa, Kurnool, Mahaboobnagar, Nalgonda, Prakasam, Rangareddy • Munger, Nawadha, Palamau, Rphtas, Bhojpur, Gaya • Ahmedabad, Amrely, Banaskanta, Bhavanagar, Bharuch, Jamnagar, Kheda, Kutch, Meshana, Panchmahal, Rajkot, Surendranagar • Bhewani, Gurgaon, Mahendragarh, Rhotak • Doda, Udhampur • Bangalore, Belgaum , Bellary, Bijapur, Chitradurga, Chickmangalur, Dharwad, Gulbarga, Hassan, Kolar, Mandya, Mysore, Raichur, Tumkur • Betul, Datia, Dewas, Dhar, Jhabuva, Khandak, Khargaon, Shandol, Shahjanpur, Sidh i, Ujjain • Ahmednagar, Aurangabad, Beed, Nanded, Nashik, Osmanabad, Pune, Parbhani, Singli, Satara, Sholapur • Phulbani, Kalahandi, Bolangir, Kendrapada
- 29. Thanks