Flood and Drought Occurrence

Flood and Drought Occurrence

Drought

Drought is a complex, slow-onset phenomenon of ecological challenge that affects people more than any other natural hazards by causing serious economic, social and environmental losses in both developing and developed countries.
The period of unusual dryness (i.e. drought) is a normal feature of the Climate and weather system in semi-arid and arid regions of the tropics, which covers more than one-third of the land surface and is vulnerable to drought and Desertification.
A drought is an extended period where water availability falls below the statistical requirements for a region.
Drought is not a purely physical phenomenon, but instead is interplay between natural water availability and human demands for water supply.
There is no universally accepted definition of drought. It is generally considered to be occurring when the principal monsoons, i.e. southwest monsoon and northeast monsoon, fail or are deficient or scanty.
Monsoon failure causing crop failure, drying up Ecosystems and shortage of drinking water results in undue hardship to the rural and urban communities.
Although droughts are still largely unpredictable; they are a recurring feature of the climate. Drought varies with regard to the time of occurrence, duration, intensity and extent of the area affected from year to year.
Land abuse during periods of good rains and its continuation during periods of deficient rainfall is the combination that contributes to desertification.
Dry regions in India include about 94 mha and about 300 million people (one-third of India’s Population) live in these areas; more than 50% of the region is affected by drought once every four years.
Different countries and states have developed codes, manuals, procedures, processes and policies for monitoring and management of drought with varying understanding.
Over the years, India has developed a fairly elaborate governance system of institutionalized drought monitoring, declaration and mitigation at different levels.
India’s response to the need for enhanced drought management has contributed to overall development. For example, the drought of 1965–1967 encouraged the ‘Green Revolution’, after the 1972 drought EMPLOYMENT generation programmes were developed for the rural poor; the 1987–1988 drought relief effort focused on preserving the Quality Of Life.

Drought Classification systems

Classification by British Rainfall Organization (BRO, 1936)

Absolute drought -When there are at least 15 consecutive days with less than 0.01 inch of rainfall per day.
Partial drought -When there are at least 29 days having mean rainfall of 0.01 inch or less.
Dry spell -When 15 consecutive days receive less than 0.04 inch of rain per day.

Thornthwaite (1947) classification

Permanent drought -Characteristics of the desert climate, possibility of vegetation and agriculture only by Irrigation.
Seasonal drought -Planting dates and crop duration should be synchronized with rainy season and residual moisture storage.
Contingent drought -Irregular occurrence and there is no regular season of occurrence.
Invisible drought -Occurs even when there is frequent rainfall and occurs in humid region.

Classification based on physical aspects

Agricultural drought – When Soil moisture is inadequate to support healthy Growth of crops, resulting in very low yield.
Hydrological drought – Associated with shortfalls in surface or subsurface water supply (stream flow, reservoir and lake levels, and groundwater) on a watershed or river basin-scale.
Meteorological drought -Related to the deficiency of rainfall compared to the Average mean annual rainfall of an area.

Indian National Commission on Agriculture (1978)

Meteorological drought –Normal Precipitation below 25%.
Hydrological drought – Prolonged meteorological drought and drying of reservoirs, lakes, streams and rivers, cessation of spring flows and fall in groundwater levels.
Agricultural drought -Depletion of soil moisture during the growing season. A dry situation with 20% Probability and rainfall deficiency of more than 25% in drought-prone states of India

Occurrence and effects of droughts in India during 1900–2002

July 2002 —–Uttar Pradesh, Madhya Pradesh, Rajasthan, Punjab, Haryana, Delhi, Karnataka, Kerala, Nagaland, Orissa, Chhattisgarh, Himachal Pradesh Gujarat, Maharashtra, Andhra Pradesh and Tamil Nadu —–300,000,000 affected; damage – US$ 910,721,000
May 2001 —–New Delhi, Rajasthan, Gujarat, Orissa ——-20 deaths
November 2000 —–Mahasamund, Raipur, Kawardha, Rajnandgaon and Durg districts in Chhattisgarh region
April 2000 —–Gujarat, Rajasthan, Madhya Pradesh, Orissa, Andhra Pradesh and Maharashtra —–90,000,000 affected; damage – US$ 588,000,000
March 1996 —–Rajasthan
March 1993 —–Bihar, Orissa, Andhra Pradesh, Maharashtra, Gujarat, Madhya Pradesh, Uttar Pradesh and Karnataka —–1,175,000 affected
July 1987 —–Orissa —–110 deaths
1987 —–Gujarat, Rajasthan, Orissa, Madhya Pradesh, Andhra Pradesh, Maharashtra and four Union Territories —–300 deaths, 300,000,000 affected
11 April 1983 —–Kerala, Tamil Nadu and Rajasthan —–100,000,000 affected
1972 —–Central India 100,000,000 affected; damage – US$ 50,000,000
August 1964 —–Mysore —–166,000,000 affected
1964 —–Rajasthan, center —–500,000 affected
1942 —–Kolkatta, Bengal region —–1,500,000 deaths
1900 —–West Bengal —–1,250,000 deaths

Preventive measures and preparedness plan for drought mitigation

Dams/reservoirs and wetlands to store water
Improvement in agriculture through modifying Cropping patterns and introducing drought-resistant varieties of crops
- Watershed Management
- Water rationing
Management of rangeland with improvement of grazing patterns, introduction of feed and protection of shrubs and trees
- Cattle management
- Proper selection of crop for drought-affected areas
- Development of water resource system with improved irrigation, development of improved storage facilities, protection of surface water from Evaporation and introduction of drop irrigation system
- Levelling, soil-conservation techniques
- Reducing deforestation and fire-wood cutting in the affected areas
Alternative land-use models for water sustainability
- Checking of Migration and providing alternate employment
Animal Husbandry activities can help in mitigation with use of improved and scientific methods
- Education and training to the people
- Participatory community programmes

Floods

Floods are high stream flows, which overlap natural or artificial banks of a river or a stream and are markedly higher than the usual as well as inundation of low land.
Sometimes copious monsoon rains combine with massive flows from the rivers, then the floods indeed become calamitous.
Through geophysical studies, it has been found that more than one and half billion people on the earth planet reside on riverside or coastal flood plains where they produce 1/3 of world’s food production.
At least- some fraction of these plains go under flood water one or the other day, hence causing widespread losses to human lives, devastated homes and heads of cattle dead, destroy agricultural crops and disrupt the Communication links such as railways, roads as well Health hazards (i.e. spread of diseases such as cholera or Gastrointestinal symptoms, etc.).
Even after the receding of floods, it takes several months or even years for the community to come to the pre-flood status.
The vulnerability of states or Union Territories of India due to floods was not observed seriously in the past due to low developmental activities and less population pressure.
However, in the present time, unabated population and high rate of developmental activities have forced the people to occupy the flood plains and making the Society highly vulnerable for flood losses.
Other factors like lack of adequate sites for rescue operations above flood levels, accessed routes for reaching these sites, lack of public information system for escape routes and other appropriate response activities may be rendered to make communities more sensitive.
The protected area (32 mha) sometimes becomes more vulnerable to floods as the flood control measures mainly the embankments may breach during a severe flood and the protected area may be inundated.
In India, 25 states and one Union Territory (Andaman & Nicobar) are susceptible to floods. However, the most vulnerable states in India are Uttar Pradesh, Bihar, Assam, West Bengal, Gujarat, Orissa, Andhra Pradesh, Madhya Pradesh, Maharashtra, Punjab and Jammu & Kashmir. District wise, there are 137 districts vulnerable to floods

CAUSES: The primary causes for Floods are-

Excessive rainfall in river catchments or concentration of runoff from the tributaries and river carrying flows in excess of their capacities.
Backing water in tributaries at their confluence with the main river.
Synchronization of flood peaks in the main rivers or their tributaries.
Intense rainfall when river is flowing full.
Poor natural Drainage System.
Landslides leading to obstruction of flow and change in the river course.
Cyclone and very intense rainfall when the El Nino effect is on a decline.

AREA PRONE TO FLOODS

Generally, the floods are caused due to the concentrated spells of heavy rains in the upper reaches of river during the monsoon months (June- September).
The South- west monsoon accounts for 75% to 90% annual rainfall of the country.
Thus, the irregular and erratic distributions of rains in different parts of the country during monsoon are the reasons for loss of lives, property and agricultural crops in the wake of floods.
Brahmaputra and the Gangetic Basins are the most flood prone areas.
The other flood prone areas are the northwest region of west flowing rivers such as the Narmada and Tapti, Central India and the Deccan region with major east flowing rivers like Mahanadi, Krishna and Cavery.
The area liable to floods is 40 million hectares (98.8 million acres) as assessed by Rashtriya Barh Ayog (RBA) in 1980; the average area affected by floods annually is about 8 million hectares covering Uttar Pradesh with 21.9%, Bihar (12.71%), Assam (9.4%), West Bengal (7.91%), Orissa (4.18%) and other states have 43.9% flood prone areas.
The heavy rain in the Himalayas at the peak of the South- West Monsoon causes severe floods in the Rivers of Uttar Pradesh, Bihar, West Bengal, and Assam, while Central & Southern Rivers get flooded on account of heavy rain produced by depressions in Bay of Bengal during Southwest monsoon season. In most flood prone states, land depression and well marked low pressure/ low-pressure areas are the two most important synoptic systems responsible for devastating floods.
In case of Bihar, 62% cases of the flood occurred due to well-marked low pressure/low pressure area, while the remaining 38% cases, flood occurred due to Land depression.
In West-Bengal, the most favorable significant situation for occurrence of flood is either low-pressure area or the cyclonic circulation.
Similar is the case for Punjab, Gujarat, Rajasthan and Jammu & Kashmir where devastating flood occurred mostly due to Low-pressure area.
The monsoon depression plays an important role in occurrence of the flood in the states like Orissa and Andhra Pradesh.
During the period of 1980-99, 53 cases of floods are identified, out of which:
25 cases (47%) – due to either low pressure or well-marked Low-pressure area
18 cases (34%) – due to either depression over land area
7 cases (13%) – due to cyclonic circulation, and
3 cases (1%) – due to cyclonic storm

TYPES OF FLOODS

Flash floods

Such floods that occur within Six hours during heavy rainfall and are usually associated with towering cumulus clouds, severe thunderstorms, and tropical Cyclones-2/”>Cyclones or during the passage of cold weather fronts.
This type of flood requires rapid localized warning system and immediate response in favour of affected communities.
Other causes of flash floods include dam failure or other river obstructions.

River floods –

Such floods are caused by precipitation over large catchment’s areas or by melting of snow or sometimes both.
They take place in river systems with tributaries that may cover or drain large geographical area and encompass many independent river basins.
These floods are normally built up slowly or on seasonl basis and may continue for days or weeks as compared to flash floods.
Factors such as ground conditions like moisture, vegetation cover, depth of snow, etc. and size of the catchments govern the amount of flood covering the main rivers of India like Ganga, Brahmaputra and Yamuna, etc.

Coastal Floods –

Some floods are associated with the cyclonic activities like Hurricanes, Tropical cyclones, etc. generating catastrophic flood from rainwater which often aggravate wind-induced storm and water surges along the coast.
As in river floods, intense rain falling over a large geographic area produces extreme flood situation in coastal river basins.

Approach to flood management

Approaches to dealing with floods may be any one or a combination of the following available Options:

Attempts to modify the flood
Attempts to modify the sus-ceptibility to flood damage
Attempts to modify the loss burden
Bearing the loss.

The main thrust of the flood protection programme undertaken in India so far has been an attempt to modify the flood in the form of physical (structural) measures to prevent the floodwaters from reaching potential damage centres and modify susceptibility to flood damage through early warning systems.

Structural measures

The following structural measures are generally adopted for flood protection:

Embankments, flood walls, sea walls
Dams and reservoirs
Natural detention basins
Channel improvement
Drainage improvement
Diversion of flood waters

Non-structural measures

Non-structural measures include:

Flood forecasting and warning
Floodplain zoning
Flood fighting
Flood proofing
Flood insurance.

Floods and droughts are two of the most common and destructive natural hazards. They can cause widespread damage to property and Infrastructure-2/”>INFRASTRUCTURE, as well as loss of life.

Floods are caused by an excess of water in an area, which can be due to heavy rainfall, snowmelt, or a combination of both. Droughts, on the other hand, are caused by a lack of rainfall, which can lead to water shortages, crop failures, and wildfires.

Both floods and droughts can have a devastating impact on communities. Floods can cause widespread damage to homes and businesses, as well as infrastructure such as roads and bridges. They can also lead to loss of life, as people are swept away by floodwaters or trapped in their homes. Droughts can lead to crop failures, which can have a devastating impact on the agricultural sector. They can also lead to water shortages, which can affect drinking water supplies, irrigation, and industrial uses.

There are a number of things that can be done to mitigate the effects of floods and droughts. One important measure is to build flood defences, such as levees and dams. These can help to protect communities from flooding. Another important measure is to develop drought-resistant crops. These crops can help to ensure that there is enough food to eat even during periods of drought.

It is also important to be prepared for floods and droughts. This includes having a plan in place for what to do if a flood or drought occurs. It is also important to have an emergency kit that includes food, water, and other supplies.

Floods and droughts are a natural part of the Earth’s climate system. However, human activities are making them more frequent and severe. Climate Change is causing more extreme weather events, including more intense rainfall and longer periods of drought. This is making floods and droughts more likely and more damaging.

There are a number of things that can be done to reduce the Impact Of Climate Change on floods and droughts. One important measure is to reduce greenhouse gas emissions. This will help to slow the rate of climate change and reduce the risk of extreme weather events. Another important measure is to adapt to the effects of climate change. This includes building flood defences, developing drought-resistant crops, and developing plans for how to respond to floods and droughts.

Floods and droughts are a serious threat to communities around the world. However, there are a number of things that can be done to mitigate the effects of these natural hazards. By taking action to reduce greenhouse gas emissions and adapt to the effects of climate change, we can reduce the risk of floods and droughts and protect our communities from these devastating events.

In addition to the subtopics listed above, there are a number of other factors that can contribute to floods and droughts. These include:

Land use: Changes in land use, such as deforestation or Urbanization, can affect the way that water flows through an area. This can increase the risk of flooding in some areas and drought in others.
Climate change: Climate change is causing the Earth’s temperature to rise. This is leading to more extreme weather events, including more intense rainfall and longer periods of drought.
Human activity: Human activities, such as deforestation and pollution, can also contribute to floods and droughts.

Floods and droughts can have a devastating impact on communities. However, there are a number of things that can be done to mitigate the effects of these natural hazards. By taking action to reduce greenhouse gas emissions and adapt to the effects of climate change, we can reduce the risk of floods and droughts and protect our communities from these devastating events.

What is a flood?

A flood is an overflow of water that submerges land that is usually dry. Floods can be caused by heavy rains, snowmelt, or dam failures.

What is a drought?

A drought is a long period of time with little or no rain. Droughts can cause water shortages, crop failures, and wildfires.

What are the causes of floods and droughts?

Floods and droughts can be caused by a variety of factors, including:

Climate change: Climate change is causing the Earth’s Atmosphere to warm, which is leading to more extreme weather events, such as heavy rains and droughts.
Deforestation: Deforestation can lead to soil erosion, which can make land more susceptible to flooding.
Dams: Dams can block the flow of water, which can lead to flooding downstream.
Urbanization: Urbanization can lead to the development of impervious surfaces, such as roads and parking lots, which can prevent water from soaking into the ground and can lead to flooding.

What are the effects of floods and droughts?

Floods and droughts can have a devastating impact on people, property, and the Environment. Some of the effects of floods and droughts include:

Loss of life: Floods and droughts can cause loss of life due to drowning, injuries, and exposure to extreme weather conditions.
Property damage: Floods and droughts can cause damage to homes, businesses, and infrastructure.
Health problems: Floods and droughts can lead to health problems, such as respiratory infections, skin problems, and gastrointestinal problems.
Economic problems: Floods and droughts can lead to economic problems, such as job losses, business closures, and crop failures.

What can be done to prevent floods and droughts?

There are a number of things that can be done to prevent floods and droughts, including:

Reduce greenhouse gas emissions: Reducing greenhouse gas emissions can help to mitigate the effects of climate change, which is a major cause of floods and droughts.
Plant trees: Trees can help to prevent soil erosion and can also help to regulate the water cycle.
Build dams and levees: Dams and levees can help to control the flow of water and can reduce the risk of flooding.
Improve water management: Improved water management can help to ensure that water is used efficiently and that there is enough water to meet the needs of people and the environment.
Educate the public: Educating the public about the risks of floods and droughts can help people to take steps to protect themselves and their property.

What can be done to mitigate the effects of floods and droughts?

There are a number of things that can be done to mitigate the effects of floods and droughts, including:

Prepare for floods and droughts: Preparing for floods and droughts can help to reduce the risk of loss of life and property. Some things that can be done to prepare for floods and droughts include:
- Creating a flood and drought plan
- Stocking up on supplies
- Making sure your home is in good repair
- Knowing your evacuation route
Respond to floods and droughts: Responding to floods and droughts can help to minimize the damage and suffering caused by these events. Some things that can be done to respond to floods and droughts include:
- Providing emergency assistance
- Repairing damage
- Restoring infrastructure
- Providing disaster relief
Recover from floods and droughts: Recovering from floods and droughts can help communities to rebuild and thrive. Some things that can be done to recover from floods and droughts include:
- Providing financial assistance
- Providing counseling and support
- Rebuilding infrastructure
- Promoting Economic Development

What is the main cause of floods?
(A) Heavy rains
(B) Melting snow
(C) Dam failures
(D) All of the above
What is the main cause of droughts?
(A) Lack of rainfall
(B) High temperatures
(C) High winds
(D) All of the above
What are some of the effects of floods?
(A) Damage to property
(B) Loss of life
(C) Erosion
(D) All of the above
What are some of the effects of droughts?
(A) Crop failures
(B) Water shortages
(C) Wildfires
(D) All of the above
What are some of the ways to prevent floods?
(A) Build levees
(B) Plant trees
(C) Develop floodplain management plans
(D) All of the above
What are some of the ways to prevent droughts?
(A) Conserve water
(B) Desalination
(C) Rainwater harvesting
(D) All of the above
What is the difference between a flood and a drought?
(A) A flood is a natural disaster that occurs when water overflows its banks, while a drought is a natural disaster that occurs when there is a lack of rainfall.
(B) A flood is a natural disaster that occurs when water overflows its banks, while a drought is a man-made disaster that occurs when there is a lack of rainfall.
(C) A flood is a natural disaster that occurs when water overflows its banks, while a drought is a natural disaster that occurs when there is a lack of water in the atmosphere.
(D) A flood is a natural disaster that occurs when water overflows its banks, while a drought is a natural disaster that occurs when there is a lack of water in the soil.
What are some of the ways to mitigate the effects of floods?
(A) Build levees
(B) Plant trees
(C) Develop floodplain management plans
(D) All of the above
What are some of the ways to mitigate the effects of droughts?
(A) Conserve water
(B) Desalination
(C) Rainwater harvesting
(D) All of the above
What is the role of the government in preventing and mitigating the effects of floods and droughts?
(A) The government should provide funding for flood control and drought relief efforts.
(B) The government should develop and implement policies to reduce the risk of floods and droughts.
(C) The government should educate the public about the risks of floods and droughts.
(D) All of the above