http://drought.unl.edu/Planning/Monitoring/ComparisonofIndicesIntro/PDSI.aspx
DROUGHT
What is Drought?• Drought is either the absence or deficiency of rainfall from its normal
pattern in a region for an extended period of time leading to general suffering of the population of that region.
• Drought is an extended period when a region receives a deficiency in its water supply, whether atmospheric, surface or ground water.
• A drought can last for months or years, or may be declared after as few as 15 days.
• Generally, this occurs when a region receives consistently below average precipitation.
• It can have a substantial impact on the ecosystem and agriculture of the affected region.
• Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm to the local economy.
• Prolonged droughts have caused mass migrations and humanitarian crises.
Megadrought• A megadrought is a prolonged drought lasting two decades or longer. Past
megadroughts have been associated with persistent multiyear La Niña conditions (cooler than normal water temperatures in the tropical eastern Pacific Ocean).
• Multiyear droughts of less than a decade, such as the Dust Bowl drought of the 1930s, are generally not described as megadroughts even though they are of a long duration.
• Megadroughts have historically led to the mass migration of humans away from drought affected lands, resulting in a significant population decline from pre-drought levels. They are suspected of playing a primary role in the collapse of several pre-industrial civilizations, including the Anasazi of the North American Southwest, the Khmer Empire of Cambodia, the Mayan of Mesoamerica, the Tiwanaku of Bolivia, and the Yuan Dynasty of China.
• The African Sahel region in particular has suffered multiple megadroughts throughout history, with the most recent lasting from approximately 1400 AD to 1750 AD. North America experienced at least four megadroughts during the Medieval Warm Period.
Some features of Drought• It is a slow on-set disaster and it is difficult to
demarcate the time of its onset and end.• Any unusual dry period which results in a water
shortage of useful water.• Drought can occur by improper distribution of rain
in time and space, and not just by its amount.• Drought is a negative balance between
precipitation and water use (through evaporation, transpiration by plants, domestic and industrial uses, etc.) in a geographical region.
An Eye-opener:
• About 2.7% of the total water available on the Earth is fresh water, of which about 75.2% lies frozen in Polar Regions and another 22.6% is present as ground water.
• The rest is available in lakes, rivers, atmospheric moisture, within soil, and in vegetation.
• Parts of this water is now polluted or is threatened with pollution.
• Today, we have approximately the same amount of water as when the Earth was formed billions of years ago!
• The Earth will not be getting or generating any more water in the future, what we have is all we have!
• We are using up the fresh water supplies we do have faster than we are recharging our groundwater where it is coming from!
India
• India has over 16% of the worlds population BUT only 4% of the total available fresh water!
• Groundwater, which is 38.5% of the available water resources of the country, plays a major role in irrigation, rural water supply, and even in meeting industrial & drinking water needs.
• Groundwater meets 55% of irrigation, 85% of rural, and 50% of urban and industrial needs.
Types of Droughts:• Meteorological Drought – the simple absence or
deficit of rainfall from the normal weather conditions.• Hydrological Drought – the reduction of natural river
& stream flows or ground water levels, plus reduced stored water supplies. The main impact is on the water resource systems.
• Agricultural Drought – occurs when moisture levels in the soil is insufficient to maintain average crop yeilds. An extreme agricultural drought can lead to a famine causing widespread malnutrition and outbreaks of disease (epidemics & pandemics) in addition to death from starvation.
Causes of Drought• Prolonged scanty rainfall causes drought.• Environmental Degradation, especially the loss of
green cover which affects rainfall received in the region, increasing the possibility of water stress.
• What causes Environmental Degradation?– Deforestation– Soil Erosion– Excessive use of ground or surface water– Loss of biodiversity– Global Warming
Vulnerability Factors:• Low soil moisture holding
capacity• Absence of irrigation
facilities• Livestock without
adequate fodder• Storage facilities• Poor water management• Deforestation• Overgrazing
• Water consuming cropping patterns
• Soil erosion• Population growth and
urbanization• Industrialization• Global Warming• El Niño & La Niña weather
conditions
Drought Mathematics• Onset of Drought – Deficiency of a particular year’s rainfall
exceeding 25% of normal.• Abnormally Dry – Going into drought, short-term
dryness/Coming out of drought, some lingering water deficits.• Moderate Drought – Deficit of rainfall between 26% & 50% of
normal, low well water levels, some water shortages developing or imminent.
• Severe Drought – Deficit of rainfall more than 50% of normal, water shortages common, water restrictions imposed.
• Extreme Drought – Widespread water shortages or restrictions.• Exceptional Drought – Exceptional and widespread shortages of
water in reservoirs, streams, and wells creating water emergencies.
http://droughtmonitor.unl.edu/Home.aspx
• Short-term drought is typically less than 6 months
• Long-term drought is typically more than 6 months
California Drought conditions one year ago – 29 OCT 2013
Relief Measures in Drought• Contingency Crop Planning• Relief Employment• Water Resources Management• Food Security• Gratuitous Assistance• Relief through Tax Waivers and Concessions• Cattle Camps and Fodder Supply• Health and Hygiene• Institutional Response• Use of Relief Agencies
Long-term Mitigation Strategies• Construction of Community Based Rain Water
Harvesting Structures.• Promoting Watershed Programmes.• Increasing Forest Cover through plantations.• Adopting drought resistant varieties of crops.• Using alternative crops in drought conditions.• Capacity building of communities in drought
management & introducing livelihood options besides agriculture and animal husbandry which are water intensive.
• Encouraging crop and seed insurance schemes.
Important “DON’Ts” in Drought Prone areas
• Misuse or waste precious water resources.• Destroy natural vegetation such as forests, pastures,
trees, etc.• Overgraze domestic animals.• Grow water-loving plants in water scarce areas.• Promote monoculture, and encourage mixed
cropping.
Beyond Drought
• Drought is an insidious natural hazard with far-reaching impacts that range from economic losses to loss of agriculture and livelihood.
• Drought can cause or exacerbate water, food, and national security hazards.
Global Drought ConditionsSeptember 2014
