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Subject: Geography

  • Dam safety bill for sustainable water management

    dam safety billContext

    • Integrated risk assessment of dam safety required to prevent human-made disasters: Experts

    Why in news?

    • The recent floods in the Mahanadi basin in Odisha have brought to the fore, the faulty management of dam safety, which were built to mitigate floods and not be the cause of them.

    What is a dam?

    • A dam is a barrier that stops the flow of water and results in the creation of a reservoir. Dams are mainly built in order to produce electricity by using water. This form of electricity is known as hydroelectricity.
    • Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquaculture, and navigability.

    Key facts

    India has 5,745 large dams according to the National Register of Large Dams, 2019, prepared by the Central Water Commission. Some 5,334 of them are operational and the remaining 411 are under construction.

    What is the Dam Safety Act, 2021?

    • The Act comprehensively postulates for surveillance, inspection, operation and maintenance of dams to prevent disasters.

    Features

    • National Committee on Dam Safety (NCDS): It will be constituted and will be chaired by the chairperson, Central Water Commission. Its’ functions will include formulating policies and regulations regarding dam safety standards and prevention of dam failures, analyzing the causes of major dam failures, and suggesting changes in dam safety practices.
    • National Dam Safety Authority (NDSA): It will be headed by an officer, not below the rank of an Additional Secretary, to be appointed by the central government. The main task of this authority includes implementing the policies formulated by the NCD, resolving issues between State Dam Safety Organisations (SDSOs), or between an SDSO and any dam owner in that state, specifying regulations for inspection and investigation of dams.
    • State Dam Safety Organisation (SDSO): Its functions will be to keep perpetual surveillance, inspection, monitoring the operation and maintenance of dams, keeping a database of all dams, and recommending safety measures to owners of dams.
    • Dam Safety Unit: The owners of the specified dams are required to provide a dam safety unit in each dam. This unit will inspect the dams before and after the monsoon session, and during and after any calamity or sign of distress.
    • Emergency Action Plan: Dam owners will be required to prepare an emergency action plan, and carry out risk assessment studies for each dam at specified regular intervals.
    • Certain offences: The act provides for two types of offences – obstructing a person in the discharge of his functions, and refusing to comply with directions issued under the proposed law.

    dam safetyDam rehabilitation and improvement programme DRIP

    • Government of India, with financial assistance from the World Bank initiated Dam Rehabilitation and Improvement Project (DRIP) in April 2012 with an objective to improve the safety and operational performance of selected existing dams along with dam safety institutional strengthening with system wide management approach. It was a State Sector Scheme with Central component.

    Do you know?

    Four dams — Mullaperiyar, Parambikulam, Thunakkadavu and Peruvaripallam — located in Kerala but owned, operated and maintained by the Tamil Nadu Government.

    Conclusion

    • The bill aims to help all States and Union Territories to adopt uniform dam safety procedures which will ensure safety of dams and safeguard benefits from such dams. In order to iron out the differences and issues in the bill, central government should take the state governments into consideration and hold talks with all the stakeholders. This will go a long way in ensuring the safety of dams in India, which ranks third in the world in terms of number of large dams.

    Mains question

    Q. India, which ranks third in the world in terms of number of large dams. Ageing dams poses several challenges for India. In this context discuss the importance of dam safety bill 2021.

     

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  • In news: Continental Drift Theory

    This newscard is an excerpt from the original article published in TH which talks about the specie Lemurs who are supposed to jump into seas to find India which got drifted away from the Madagascar.

    Study on Lemurs

    • Many life forms in Madagascar have affinities to lineages found in India (3,800 km away) rather than Africa (413 km). This posed a ‘difficult enigma’ to naturalists.
    • One such species is the Lemurs.
    • We most likely see lemurs in a Hollywood animation movie; singing, dancing and playing pranks.
    • Zoologists was perplexed by the presence of lemurs, their relatives, and their fossils in Madagascar and India, but not in nearby Africa or the Middle East.
    • In the 1860s, he proposed that a large island or continent must have once existed between India and Madagascar, serving as a land bridge.
    • Over time, this island had sunk. He called this proposed island Lemuria.

    Existence of such Island in Indian legends

    • Tamil revivalists such as Devaneya Pavanar also took up the idea, in the form of a Tamil civilisation, lost to the sea as described in literature and in Pandyan legends.
    • They called this submerged continent Kumari Kandam.

    Basis of this legend: Continental Drift Theory

    • In the early 20th century, German geologist Alfred Wegener published a paper on his theory called continental drift.
    • It is a hypothesis that Earth’s continents were moving across Earth, and sometimes, even colliding into one another.
    • According to Wegener’s theory, Earth’s continents were once joined as a single, giant landmass, which he called Pangaea.
    • But over time, Pangaea broke apart and formed the continents as we know them today.
    • Wegener couldn’t explain why this phenomenon was happening, so at the time, his theory was heavily criticized by his colleagues.
    • But over the years, technological advances allowed scientists to study the Earth more closely, and geologists started to build on Wegener’s theory.

    Rise over to Plate Tectonics

    • Discoveries like seafloor spreading helped explain the “why” behind continental movement, and eventually, Wegener’s initial continental drift theory morphed into plate tectonic theory.
    • And now, the idea that Earth’s crust is slowly moving beneath our feet is widely accepted.

    The Seven Major Tectonic Plates

    There are seven major plates, and dozens of minor plates, that make up the outer crust of the Earth. The big seven are:

    1. North American plate
    2. Eurasian plate
    3. Pacific plate
    4. South American plate
    5. African plate
    6. Indo-Australian plate
    7. Antarctic plate

     

    The areas between these plates are known as plate boundaries, and their interactions cause some crazy things to happen on Earth’s surface.

    There are three types of plate boundaries:

    1. Divergent boundary
    • A divergent boundary is when two plates move away from each other, which creates a fracture in the lithosphere.
    • A well-known divergent boundary is the Mid-Atlantic Ridge, which runs approximately 10,000 miles from the Arctic Ocean all the way down to the south of Africa.
    1. Convergent boundary
    • A convergent boundary is when two plates collide with one another.
    • If the collision is between oceanic crust and continental crust, the denser oceanic crust slides underneath the other plate, which is a process known as subduction.
    • When two continental crusts collide, the rock folds and lifts at the boundary, creating mountains like the Himalayas (where the Indian plate meets the Eurasian plate).
    1. Transform Boundary
    • When two plates move parallel to one another, their meeting point is called a transform boundary. The friction causes tension.
    • Eventually, that tension needs to be released, which can cause earthquakes.
    • The San Andreas Fault is a well-known major transform boundary between the North American and Pacific plates—it caused the infamous San Francisco earthquake of 1906.

    How do we apply this theory here?

    • A landmass called Gondwana, split into two 165 million years ago — one containing what is now Africa and South America, the other comprising India, Madagascar, Australia and Antarctica.
    • Around 115 million years ago, Madagascar and India together broke free.
    • Around 88 million years ago, India moved northward, dropping a few parcels of land along the way to form Seychelles.
    • It joined the Eurasian mass 50 million years ago giving rise to the Himalayas and South Asia that we are familiar with.
    • Around 115 million years ago, it was the dinosaurs that ruled. Many life forms had not even evolved.

    Substantiation to this study

    (1) Fossil study

    • Supporting the Gondwana breakup, dinosaur fossils found in India and Madagascar are closely related and do not resemble species found in Africa and Asia.
    • Fragments of Laplatosaurus madagascarensis have been found in both India and Madagascar.

    (2) Molecular clocks

    • A powerful technique, the molecular clock, is used to estimate the time when two forms of life diverged from each other.
    • It is based on the observation that evolutionary changes in the sequence of an RNA or a protein molecule occur at a fairly constant rate.
    • The difference in the amino acids of, say the haemoglobin of two animals can tell you how long ago their lineages diverged.
    • Molecular clocks corroborate well with other evidence, such as the fossil record.
    • South India and Sri Lanka have only two genuses of the cichlid family of freshwater and brackish-water fishes — the Etroplus (a food fish in Kerala, where it is called pallathi) and Pseudetroplus.
    • Molecular comparisons show that the nearest relatives of Etroplus are found in Madagascar, and their common ancestor diverged from African cichlids 160 million years ago.

    India’s pivotal position

    • India occupies a pivotal position in the distribution of life forms in Asia, Madagascar and Africa. Gondwana creatures moved out of India.
    • Others crossed over to stay. For example, Asian freshwater crabs (Gecarcinucidae) are now found all over Southeast Asia but their most recent common ancestor evolved in India.
    • Fossil finds in the Vastan lignite mine in Gujarat by researchers have identified the earliest Indian mammal, a species of bat, and the earliest euprimate, a primitive lemur.
    • These were dated 53 million years ago, around the time (or just before) the India-Eurasian plates collided.

    What about the lemurs?

    • Madagascar is a large island, with a variety of climatic conditions. Evidence favours an ancestor primate crossing over from Africa.
    • No monkey, ape or large predator managed the crossing, so dozens of lemur species proliferated.
    • In India, we have the lorises, which are the closest extant relatives of the lemurs.
    • These are shy, nocturnal forest dwellers, with large, appealing eyes.
    • They are also believed to have survived oceanic rides from Africa.
    • They are mostly found in the Northeastern States (slow loris), and where Karnataka, Kerala and Tamil Nadu meet (slender loris).

     

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  • What are Tetrapods?

    In Mumbai, the unusual vibrations (like earthquakes), coinciding with high-tide times, were the result of the relocation of tetrapods as part of the ongoing Coastal Road Project (MCRP).

    What are tetrapods?

    • Tetra pod in Greek means four-legged.
    • These are four-legged concrete structures that are placed along coastlines to prevent erosion and water damage.
    • Tetrapods were first used in France in the late 1940s to protect the shore from the sea.
    • They are typically placed together to form an interlocking but porous barrier that dissipates the power of waves and currents.
    • These are large structures, sometimes weighing up to 10 tonnes, and interlocked tetra pods act as a barrier that remains stable against the rocks when buffeted by waves.
    • Tetrapods, each weighing about 2 tonnes, were placed along Marine Drive in the late 1990s to break and dissipate waves and maintain the reclaimed shoreline in South Mumbai.

    How do we know that the removal of the tetrapods was responsible?

    • The BMC has provided vibration monitoring instruments at the site to study the impact of the phenomenon.
    • While the corporation has not officially stated that the removal of the tetrapods caused the vibrations, it has agreed to re-install the structures.
    • They would be put back over the next two-three days during low tide.

     

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  • Derecho: A storm that turned the sky green in the US

    States of Nebraska, Minnesota and Illinois in the US were hit by a storm system called a Derecho which turned the skies green.

    What is a Derecho?

    • A derecho is a widespread, long-lived, straight-line windstorm that is associated with a band of rapidly moving showers or thunderstorms.
    • The name comes from the Spanish word ‘la derecha’ which means ‘straight’.
    • Straight-line storms are those in which thunderstorm winds have no rotation unlike a tornado.
    • Being a warm-weather phenomenon, a derecho generally – not always – occurs during summertime beginning May, with most hitting in June and July.
    • However, they are a rare occurrence as compared to other storm systems like tornadoes or hurricanes.

    Why does the sky turn green during the derecho?

    • Severe thunderstorms result in a ‘green sky’ due to light interacting with the huge amount of water they hold.
    • The big raindrops and hail scatter away all but the blue wavelengths due to which primarily blue light penetrates below the storm cloud.
    • This blue then combines with the red-yellow of the afternoon or the evening sun to produce green.

    Are there different types of derechos?

    They fall into three categories – progressive, serial and hybrid.

    1. Progressive derecho is associated with a short line of thunderstorms that may travel for hundreds of miles along a relatively narrow path. It is a summer phenomenon.
    2. Serial derecho, on the other hand, has an extensive squall line – wide and long – sweeping across a large area. It usually occurs during spring or fall.
    3. Hybrid derecho are that ones have the features of both progressive and serial derechos.

    Where do derechos usually occur?

    • They mostly occur across central and eastern parts of the United States.
    • Derechos have also been documented elsewhere across the world.
    • In 2010, Russia witnessed its first documented derecho.
    • They have also swept through Germany and Finland, and more recently in Bulgaria and Poland.

     

     

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  • Earthquake in Afghanistan

    Recently a powerful earthquake of magnitude 5.9 on the Richter scale struck a remote town in Afghanistan, killing over a thousand and injuring many more.

    How do earthquakes happen?

    • According to the theory of plate tectonics, the Earth’s crust and upper mantle are made of large rigid plates that can move relative to one another.
    • Slip on faults near the plate boundaries can result in earthquakes.
    • The point inside the Earth where the earthquake rupture starts is called the focus or hypocentre.
    • The point directly above it on the surface of the Earth is the epicentre.

    What are Seismic Waves?

    • Any elastic material when subjected to stress, stretches in a proportional way, until the elastic limit is reached.
    • When the elastic limit is crossed, it breaks.
    • Similarly, the Earth also has an elastic limit and when the stress is higher than this limit, it breaks.
    • Then there is a generation of heat, and energy is released. Since the material is elastic, the energy is released in the form of elastic waves.
    • These propagate to a distance determined by the extent of the impact. These are known as seismic waves.

    Why Earthquake in Afghanistan?

    • Afghanistan is earthquake-prone because it’s located in the mountainous Hindu Kush region, which is part of the Alpide belt — the second most seismically active region in the world after the Pacific Ring of Fire.
    • The Alpide belt runs about 15,000 kilometers, from the southern part of Eurasia through the Himalayas and into the Atlantic.
    • Along with the Hindu Kush, it includes a number of mountain ranges, such as the Alps, Atlas Mountains and the Caucasus Mountains.
    • Additionally, the Earth’s crust is especially lively in Afghanistan because it is where the Arabian, Indian and Eurasian tectonic plates meet.
    • The boundary between the Indian and Eurasian plates exists near Afghanistan’s border with Pakistan.

    How are earthquakes measured?

    • Earthquakes are measured by seismographic networks, which are made of seismic stations, each of which measures the shaking of the ground beneath it.
    • In India, the National Seismological Network does this work.
    • It has a history of about 120 years and its sensors can now detect an earthquake within five to ten minutes.

    Issues with Earthquake measurement

    • Everywhere, the wave parameters are measured, not the total energy released.
    • There is a direct relationship between the quantum of energy released and the wave amplitude.
    • The amplitude of the wave is a function of the time period of the wave.
    • It is possible to convert the measured wave amplitude into the energy released for that earthquake.
    • This is what seismologists call the magnitude of the earthquake.

    What is the Richter magnitude scale?

    • This is a measure of the magnitude of an earthquake and was first defined by Charles F. Richter of the California Institute of Technology, U.S., in 1935.
    • The magnitude of an earthquake is the logarithm of the amplitude of the waves measured by the seismographs.
    • Richter scale magnitudes are expressed as a whole number and a decimal part, for example 6.3 or 5.2.
    • Since it is a logarithmic scale, an increase of the whole number by one unit signifies a tenfold increase in the amplitude of the wave and a 31-times increase of the energy released.

    How are zones designated?

    • Based on seismicity, intensity of earthquakes experienced, and geological and tectonic qualities of a region, countries are divided into several zones.
    • In India, for example, there are four zones, designated Zone II-Zone V. Among these, Zone V is the most hazardous and Zone II the least hazardous.

    Can we predict Earthquakes?

    • Since parameters of the earthquake are unknown, it is near impossible to predict an earthquake.
    • The problem with earthquakes is that they are heavily dependent on the material property, which varies from place to place.
    • If there are elastic waves propagating through a material, there are two kinds of waves — the primary wave which reaches first, and the second one called the secondary wave, which is more destructive.
    • If it is known that the amount of energy released is extremely high, trains and power grids can be shut down and the damage minimised.
    • This has worked in some locations, but not on a large commercial basis.

    Successful attempts made so far

    • The most successful early warning systems are in Japan.
    • They have several hundreds of thousands recording devices.
    • Responses are sent to a central point where they estimate whether it is large enough to form a tsunami or some other hazard, and precautionary steps are taken.

     

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  • [pib] Coalition for Disaster Resilient Infrastructure (CDRI)

    The Union Cabinet has approved the categorization of the Coalition for Disaster Resilient Infrastructure (CDRI) as an ‘International Organization’.

    What is the news?

    • The cabinet also signed as the Headquarters Agreement (HQA) with CDRI for granting it the exemptions, immunities and privileges as contemplated under the United Nations (Privileges & Immunities) Act, 1947.
    • This will provide CDRI an independent and international legal persona so that it can efficiently and effectively carry out its functions internationally.

    What is CDRI?

    • The CDRI is an international coalition of countries, UN agencies, multilateral development banks, the private sector, and academic institutions that aim to promote disaster-resilient infrastructure.
    • Its objective is to promote research and knowledge sharing in the fields of infrastructure risk management, standards, financing, and recovery mechanisms.
    • It was launched by the Indian PM Narendra Modi at the 2019 UN Climate Action Summit in September 2019.
    • CDRI’s initial focus is on developing disaster-resilience in ecological, social, and economic infrastructure.
    • It aims to achieve substantial changes in member countries’ policy frameworks and future infrastructure investments, along with a major decrease in the economic losses suffered due to disasters.

    Its inception

    • PM Modi’s experience in dealing with the aftermath of the 2001 Gujarat earthquake” as the chief minister led him to the idea.
    • The CDRI was later conceptualized in the first and second edition of the International Workshop on Disaster Resilient Infrastructure (IWDRI) in 2018-19.
    • It was organized by the National Disaster Management Authority (NDMA), in partnership with the UN Office for Disaster Risk Reduction (UNDRR), the UN Development Programme, the World Bank, and the Global Commission on Adaptation.

    Its diplomatic significance

    • The CDRI is the second major coalition launched by India outside of the UN, the first being the International Solar Alliance.
    • Both of them are seen as India’s attempts to obtain a global leadership role in climate change matters and were termed as part of India’s stronger branding.
    • India can use the CDRI to provide a safer alternative to China’s Belt and Road Initiative (BRI) as well.

    Why designated as International Organization?

    • Deputing experts to other countries
    • Deploying funds globally and receive contributions from member countries
    • Making available technical expertise to assist countries
    • Imparting assistance to countries in adopting appropriate risk governance arrangements and strategies for resilient infrastructure
    • Aligning with the Sustainable Development Goals (SDGs), the Paris Climate Agreement and the Sendai Framework for Disaster Risk Reduction
    • Leveraging international engagement to foster disaster-resilient infrastructure at home; and,
    • Providing Indian scientific and technical institution as well as infrastructure developers an opportunity to interact with global experts.

    Try this PYQ:

    Q.Consider the following statements:

    1. Climate and Clean Air Coalition (CCAC) to Reduce Short Lived Climate Pollutants is a unique initiative of G20 group of countries
    2. The CCAC focuses on methane, black carbon and hydrofluorocarbons.

    Which of the above statements is/are correct?

    (a) 1 only

    (b) 2 only

    (c) Both 1 and 2

    (d) Neither 1 nor 2

     

    [wpdiscuz-feedback id=”g1rfo9e6dp” question=”Please leave a feedback on this” opened=”1″]Post your answers here.[/wpdiscuz-feedback]

     

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  • Why Assam gets flooded every year

    Disaster struck Dima Hasao, central Assam’s hill district, in mid-May after incessant heavy rainfall.

    Impacts of the disaster

    • The 170 km railway line connecting Lumding in the Brahmaputra Valley’s Hojai district and Badarpur in the Barak Valley’s Karimganj district was severely affected.
    • The Assam government and Railway Ministry’s assessments said the district suffered a loss of more than ₹1,000 crore, but ecologists say the damage could be irreversibly higher.

    How severe has the rain been in Assam?

    • Assam is used to floods, sometimes even four times a year, resultant landslides and erosion.
    • But the pre-monsoon showers this year have been particularly severe on Dima Hasao, one of three hill districts in the State.
    • Landslips have claimed four lives and damaged roads.
    • The impact has been most severe on the arterial railway, which was breached at 58 locations leaving the track hanging in several places.
    • The disruption of train services, unlikely to be restored soon, has cut off the flood-hit Barak Valley, parts of Manipur, Mizoram and Tripura.

    Why is the railway in focus post-disaster?

    • Dima Hasao straddles the Barail, a tertiary mountain range between the Brahmaputra and Barak River basins.
    • The district is on the Dauki fault (the prone-to-earthquakes geological fractures between two blocks of rocks) straddling Bangladesh and parts of the northeast.
    • British engineers were said to have factored in the fragility of the hills to build the railway line over 16 years by 1899.
    • The end result was an engineering marvel 221 km long over several bridges and through 37 tunnels, laid along the safer sections of the hills.

    A faulty experiment

    • A project to convert the metre gauge track to broad gauge was undertaken in 1996 but the work was completed only by March 2015 because of geotechnical constraints and extremist groups.
    • The broad-gauge track was realigned to be straighter, but a 2009-10 audit report revealed that the project had been undertaken without proper planning and visualisation of the soil strata behaviour.
    • The report gave the example of the disaster-prone Tunnel 10 on the realigned track that was pegged 8 meters below the bed of a nearby stream.

    Is only the railway at fault?

    • There is a general consensus that other factors have contributed to the situation Dima Hasao is in today.
    • Roads in the district, specifically the four-lane Saurashtra-Silchar (largest Barak Valley town) East-West Corridor, have been realigned or deviated from the old ones that were planned around rivers and largely weathered the conditions.
    • The arterial roads build over the past 20 years often cave in and get washed away by floods or blocked by landslides.
    • Shortened cycles of jhum or shifting cultivation on the hill slopes and unregulated mining have accentuated the “man-made disaster”.
    • Massive extraction of river stone, illegal mining of coal and smuggling of forest timbe has led to the disaster.
    • These activities have increased water current besides weakening either side of riverbanks.

    How vital are the rail and highway through Dima Hasao?

    • Meghalaya aside, Dima Hasao is the geographical link to a vast region comprising southern Assam’s Barak Valley, parts of Manipur, Mizoram and Tripura.
    • Moreover, this track is vital for India’s Look East policy that envisages shipping goods to and from Bangladesh’s Chittagong port via Tripura’s border points at Akhaura and Sabroom.
    • These are the last railway station near the Feni River that serves as the India-Bangladesh border.

     

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  • Devastation in Dima Hasao and its after-effects

    Disaster struck Dima Hasao, central Assam’s hill district, in mid-May after incessant heavy rainfall.

    Impacts of the disaster

    • The 170 km railway line connecting Lumding in the Brahmaputra Valley’s Hojai district and Badarpur in the Barak Valley’s Karimganj district was severely affected.
    • The Assam government and Railway Ministry’s assessments said the district suffered a loss of more than ₹1,000 crore, but ecologists say the damage could be irreversibly higher.

    How severe has the rain been in Assam?

    • Assam is used to floods, sometimes even four times a year, resultant landslides and erosion.
    • But the pre-monsoon showers this year have been particularly severe on Dima Hasao, one of three hill districts in the State.
    • Landslips have claimed four lives and damaged roads.
    • The impact has been most severe on the arterial railway, which was breached at 58 locations leaving the track hanging in several places.
    • The disruption of train services, unlikely to be restored soon, has cut off the flood-hit Barak Valley, parts of Manipur, Mizoram and Tripura.

    Why is the railway in focus post-disaster?

    • Dima Hasao straddles the Barail, a tertiary mountain range between the Brahmaputra and Barak River basins.
    • The district is on the Dauki fault (the prone-to-earthquakes geological fractures between two blocks of rocks) straddling Bangladesh and parts of the northeast.
    • British engineers were said to have factored in the fragility of the hills to build the railway line over 16 years by 1899.
    • The end result was an engineering marvel 221 km long over several bridges and through 37 tunnels, laid along the safer sections of the hills.

    A faulty experiment

    • A project to convert the metre gauge track to broad gauge was undertaken in 1996 but the work was completed only by March 2015 because of geotechnical constraints and extremist groups.
    • The broad-gauge track was realigned to be straighter, but a 2009-10 audit report revealed that the project had been undertaken without proper planning and visualisation of the soil strata behaviour.
    • The report gave the example of the disaster-prone Tunnel 10 on the realigned track that was pegged 8 meters below the bed of a nearby stream.

    Is only the railway at fault?

    • There is a general consensus that other factors have contributed to the situation Dima Hasao is in today.
    • Roads in the district, specifically the four-lane Saurashtra-Silchar (largest Barak Valley town) East-West Corridor, have been realigned or deviated from the old ones that were planned around rivers and largely weathered the conditions.
    • The arterial roads build over the past 20 years often cave in and get washed away by floods or blocked by landslides.
    • Shortened cycles of jhum or shifting cultivation on the hill slopes and unregulated mining have accentuated the “man-made disaster”.
    • Massive extraction of river stone, illegal mining of coal and smuggling of forest timbe has led to the disaster.
    • These activities have increased water current besides weakening either side of riverbanks.

    How vital are the rail and highway through Dima Hasao?

    • Meghalaya aside, Dima Hasao is the geographical link to a vast region comprising southern Assam’s Barak Valley, parts of Manipur, Mizoram and Tripura.
    • Moreover, this track is vital for India’s Look East policy that envisages shipping goods to and from Bangladesh’s Chittagong port via Tripura’s border points at Akhaura and Sabroom.
    • These are the last railway station near the Feni River that serves as the India-Bangladesh border.

     

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  • What is Onset of Monsoon?

    The monsoon is slated to make its earliest arrival in 13 years over Kerala, informs the India Meteorological Department (IMD).

    What does the “Onset of Monsoon” mean?

    • The onset of the monsoon over Kerala marks the beginning of the four-month, June to September southwest monsoon season over India.
    • It brings more than 70 per cent of the country’s annual rainfall.
    • It marks a significant transition in the large-scale atmospheric and ocean circulations in the Indo-Pacific region.
    • The IMD announces it only after certain newly defined and measurable parameters, adopted in 2016, are met.
    • The onset is a significant day in India’s economic calendar.

    How does IMD predict the monsoon?

    • Broadly, the IMD checks for the consistency of rainfall over a defined geography, its intensity, and wind speed:
    1. Rainfall: The IMD declares the onset of the monsoon if at least 60% of 14 designated meteorological stations in Kerala and Lakshadweep record at least 2.5 mm of rain for two consecutive days at any time after May 10.
    2. Wind field: The depth of westerlies should be upto 600 hectopascal (1 hPa is equal to 1 millibar of pressure) in the area bound by the equator to 10ºN latitude, and from longitude 55ºE to 80ºE. The zonal wind speed over the area bound by 5-10ºN latitude and 70-80ºE longitude should be of the order of 15-20 knots (28-37 kph) at 925 hPa.
    3. Heat: The INSAT-derived Outgoing Longwave Radiation (OLR) value (a measure of the energy emitted to space by the Earth’s surface, oceans, and atmosphere) should be below 200 watt per sq m (wm2) in the box confined by 5-10ºN latitude and 70-75ºE latitude.
    • The onset is not officially declared until the prescribed conditions (above) are met.

    Factors considered by IMD

    • The IMD uses a specialised model that forecasts the arrival dates within a four-day window.
    • It uses six predictors:
    1. Minimum temperatures over northwest India
    2. Pre-monsoon rainfall peak over south Peninsula
    3. Outgoing long-wave radiation (OLR) over the South China Sea
    4. Lower tropospheric zonal wind over the southeast Indian Ocean
    5. Upper tropospheric zonal wind over the east equatorial Indian Ocean, and
    6. OLR over the southwest Pacific region

    Where is the early arrival noticed?

    • The monsoon’s arrival over India is marked by rain over south Andaman Sea, which then advances north-westwards across the Bay of Bengal.
    • In general, the Andaman and Nicobar Islands start receiving monsoon rainfall between May 15 and May 20 every year.
    • And it usually starts raining along the Kerala coast in the last week of May.

    Does an early onset foretell a good monsoon?

    • No, it does not — just as a delay does not foretell a poor monsoon.
    • The onset is just an event that happens during the progress of the monsoon over the Indian subcontinent.
    • A delay of a few days, or perhaps the monsoon arriving a few days early, has no bearing on the quality or amount of rainfall, or its regional distribution across the country.

    Back2Basics: Long Period Average (LPA)

    • The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
    • The LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30 years, 50 years, etc.
    • LPA refers to the average rainfall recorded from June to September for the entire country, the amount of rain that falls every year varies from region to region and from month to month.
    • The IMD’s prediction of a normal monsoon is based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average.
    • It has in the past calculated the LPA at 88 cm for the 1961-2010 period, and at 89 cm for the period 1951-2000.

    Why LPA is needed?

    • The IMD records rainfall data at more than 2,400 locations and 3,500 rain-gauge stations.
    • Because annual rainfall can vary greatly not just from region to region and from month to month, but also from year to year within a particular region or month.
    • An LPA is needed to smooth out trends so that a reasonably accurate prediction can be made.
    • A 50-year LPA covers for large variations in either direction caused by freak years of unusually high or low rainfall, as well as for the periodic drought years.
    • It also takes into account the increasingly common extreme weather events caused by climate change.

    Range of normal rainfall

    The IMD maintains five rainfall distribution categories on an all-India scale. These are:

    1. Normal or near normal, when the percentage departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA;
    2. Below normal, when departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA;
    3. Above normal, when actual rainfall is 104-110% of LPA;
    4. Deficient, when departure of actual rainfall is less than 90% of LPA; and
    5. Excess, when the departure of actual rainfall is more than 110% of LPA.

    Also read

    Various terms related to Indian Monsoon

     

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  • What is the ‘Long Period Average’, IMD’s benchmark for monsoon prediction?

    India is likely to receive a normal monsoon for the fourth consecutive year, the India Meteorological Department (IMD) said in its first Long Range Forecast (LRF) for this year.

    What is Long Period Average (LPA)?

    • The IMD predicts a “normal”, “below normal”, or “above normal” monsoon in relation to a benchmark “long period average” (LPA).
    • The LPA of rainfall is the rainfall recorded over a particular region for a given interval (like month or season) average over a long period like 30 years, 50 years, etc.
    • LPA refers to the average rainfall recorded from June to September for the entire country, the amount of rain that falls every year varies from region to region and from month to month.
    • The IMD’s prediction of a normal monsoon is based on the LPA of the 1971-2020 period, during which India received 87 cm of rain for the entire country on average.
    • It has in the past calculated the LPA at 88 cm for the 1961-2010 period, and at 89 cm for the period 1951-2000.

    Why LPA is needed?

    • The IMD records rainfall data at more than 2,400 locations and 3,500 rain-gauge stations.
    • Because annual rainfall can vary greatly not just from region to region and from month to month, but also from year to year within a particular region or month.
    • An LPA is needed to smooth out trends so that a reasonably accurate prediction can be made.
    • A 50-year LPA covers for large variations in either direction caused by freak years of unusually high or low rainfall, as well as for the periodic drought years.
    • It also takes into account the increasingly common extreme weather events caused by climate change.

    Range of normal rainfall

    The IMD maintains five rainfall distribution categories on an all-India scale. These are:

    1. Normal or near normal, when the percentage departure of actual rainfall is +/-10% of LPA, that is, between 96-104% of LPA;
    2. Below normal, when departure of actual rainfall is less than 10% of LPA, that is 90-96% of LPA;
    3. Above normal, when actual rainfall is 104-110% of LPA;
    4. Deficient, when departure of actual rainfall is less than 90% of LPA; and
    5. Excess, when the departure of actual rainfall is more than 110% of LPA.

    Also read:

    Various terms related to Indian Monsoon

     

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