💥Join UPSC 2027,2028 Mentorship (July Batch) + XFactor Notes & Microthemes PDF
Talk to Mentor

Civilsdaily

Login

Subject: Geography

  • Tide–Rainfall Flood Quotient

    To understand if a coastal city is more prone to floods caused by tidal events or extreme rainfall, a team from the IIT Bombay devised a new metric or measure called the Tide–Rainfall Flood Quotient.

    Try this PYQ:

    The 2004 Tsunami made people realize that mangroves can serve as a reliable safety hedge against coastal calamities. How do mangroves function as a safety hedge?

    (a) The mangrove swamps separate the human settlements from the sea by a wide zone in which people neither live nor venture out

    (b) The mangroves provide both food and medicines which people are in need of after any natural disaster

    (c) The mangrove trees are tall with dense canopies and serve as art excellent shelter during a cyclone or tsunami

    (d) The mangrove trees do not get uprooted by storms and tides because of their extensive roots

    Tide–Rainfall Flood Quotient

    • Using the past rainfall data, tidal data, and topography of the region one can apply this framework to pinpoint the major factor at play.
    • This quotient helps understand the main driver of the flooding events for effective disaster management.
    • It considers three geographically diverse flood-prone coastal regions – Mithi Catchment in Mumbai, , Jagatsinghpur District in Odisha, and Greater Chennai to test their new metric.
    • The new method helped classify these regions into ‘storm-tide dominated’ or ‘pluvial (rainfall) dominated’ regions.
    • In Mithi, they found a devastating impact of storm-tide reaching even up to a distance of 7 km from the coastal boundary.
    • It concluded that Mithi catchment was ‘storm-tide dominated’, while Jagatsinghpur and Chennai were ‘pluvial dominated’

    A tool for flood management

    • This metric can help disaster management experts in framing better flood risk management systems directed towards long term planning.
    • For storm-tide dominated regions, severe flood hazard can be alleviated by building coastal defence structures such as closure dams, tide breakers, and storm-surge barriers at appropriate locations.
    • The tide and surge forecasting systems in these regions should be equipped with state-of-the-art ocean circulation models.
    • On the other hand, for pluvial dominated regions, structural measures such as rainwater storage structures, lakes, and detention basins should be prioritized in the flood management plans.

  • What is Winter Solstice?

    Yesterday, December 21, was Winter Solstice, the shortest day of the year in the Northern Hemisphere. In the Southern Hemisphere, conversely, it was Summer Solstice, the year’s longest day.

    Try this MCQ:

    Q.On 21st June, the Sun

    (a) Does not set below the horizon at the Arctic Circle

    (b) Does not set below the horizon at Antarctic Circle

    (c) Shines vertically overhead at noon on the Equator

    (d) Shines vertically overhead at the Tropic of Capricorn

    Why are the hours of daylight, not the same every day?

    • The explanation lies in Earth’s tilt.
    • And it’s not just the Earth — every planet in the Solar System is tilted relative to their orbits, all at different angles.
    • The Earth’s axis of rotation is tilted at an angle of 23.5° to its orbital plane.
    • This tilt — combined with factors such as Earth’s spin and orbit — leads to variations in the duration of sunlight than any location on the planet receives on different days of the year.

    Impact of the tilted axis

    • The Northern Hemisphere spends half the year tilted in the direction of the Sun, getting direct sunlight during long summer days.
    • During the other half of the year, it tilts away from the Sun, and the days are shorter.
    • Winter Solstice, December 21, is the day when the North Pole is most tilted away from the Sun.
    • The tilt is also responsible for the different seasons that we see on Earth.
    • The side facing the Sun experiences day, which changes to night as Earth continues to spin on its axis.

    Un-impacted regions

    • On the Equator, day and night are equal. The closer one moves towards the poles, the more extreme the variation.
    • During summer in either hemisphere, that pole is tilted towards the Sun and the polar region receives 24 hours of daylight for months.
    • Likewise, during winter, the region is in total darkness for months.

    Celebrations associated with the Winter Solstice

    • For centuries, this day has had a special place in several communities due to its astronomical significance and is celebrated in many ways across the world.
    • Jewish people call the Winter Solstice ‘Tekufat Tevet’, which marks the start of winter.
    • Ancient Egyptians celebrated the birth of Horus, the son of Isis (divine mother goddess) for 12 days during mid-winter.
    • In China, the day is celebrated by families coming together for a special meal.
    • In the Persian region, it is celebrated as Yalda or Shab-e-Yalda. The festival marks the last day of the Persian month of Azar and is seen as the victory of light over darkness.
    • Families celebrate Yalda late into the night with special foods such as ajeel nuts, pomegranates and watermelon, and recite works of the 14th century Sufi poet Hafiz Shirazi.

    In Vedic tradition

    • In Vedic tradition, the northern movement of the Earth on the celestial sphere is implicitly acknowledged in the Surya Siddhanta.
    • It outlines the Uttarayana (the period between Makar Sankranti and Karka Sankranti). Hence, Winter Solstice is the first day of Uttarayana.

  • Bihar to change Kosi’s course to save the ancient site

    The Bihar government will try to divert the course of the mighty Kosi River in Bhagalpur district to save an archaeological site discovered recently.

    Tap to read more about the Himalayan Drainage System:

    Drainage System | Part 3

    Kosi River: The Sorrow of Bihar

    • The Kosi is a trans-boundary river which flows through Tibet, Nepal and India.
    • The river crosses into northern Bihar, India where it branches into distributaries before joining the Ganges near Kursela in Katihar district.
    • Its unstable nature has been attributed course changes and the heavy silt it carries during the monsoon season, and flooding in India has extreme effects.
    • It is also known as the “Sorrow of Bihar” as the annual floods affect about 21,000 km2 of fertile agricultural lands thereby disturbing the rural economy.

    Why change its course?

    • Several priceless artefacts have been found at the Guwaradih village in Naugachhia sub-division of Bhagalpur district during the excavation of a mound.
    • These items could be 2,500-years-old and could be of interest for historians if conserved.
    • The historical sites are facing threats from the Kosi floods.
    • The Kosi currently flows around 300-400 metres from the site, while its old course is about two kilometres from the village.

    Threats posed by the move

    • Environmentalists have warned that changing the Kosi’s course could be disastrous for Bihar as seen in 2008.
    • At that time, the river had breached its mud embankments at Kushaha in Nepal.
    • The Kosi frequently changes its course naturally. If its course is artificially changed, it will cause floods and erosion in new areas, leading to massive displacement of people.
    • It then caused extensive damage to life and property downstream in five densely populated districts of northeast Bihar.
    • Some 500 people were killed and four million rendered homeless.

  • How to measure a Mountain?

    China and Nepal have announced Mount Everest is 0.86 m taller than the 8,848 m accepted globally so far.

    Try this PYQ:

    Q.When you travel to the Himalayas, you will see the following:

    1. Deep gorges
    2. U-turn river courses
    3. Parallel mountain ranges
    4. Steep gradients causing land-sliding

    Which of the above can be said to be the evidences for the Himalayas being young fold mountains?

    (a) 1 and 2 only

    (b) 1, 2 and 4 only

    (c) 3 and 4 only

    (d) 1, 2, 3 and 4

    Scaling a mountains’ height

    • The basic principle that was used earlier is very simple and uses  only trigonometry which most of us are familiar with, or at least can recall.
    • There are three sides and three angles in any triangle. If we know any three of these quantities, provided one of them is a side, all the others can be calculated.
    • In a right-angled triangle, one of the angles is already known, so if we know any other angle and one of the sides, the others can be found out.
    • This principle can be applied for measuring the height of any object that does not offer the convenience of dropping a measuring tape from top to bottom.

    Accuracy issues

    • For small hills and mountains, whose top can be observed from relatively close distances, this can give quite precise measurements.
    • But for Mount Everest and other high mountains, there are some other complications.
    • These again arise from the fact that we do not know where the base of the mountain is.

    Measuring against sea level

    • Generally, for practical purposes, the heights are measured above mean sea level (MSL). Moreover, we need to find the distance to the mountain.
    • This is done through a painstaking process called high-precision levelling. Starting from the coastline, we calculate step by step the difference in height, using special instruments.
    • This is how we know the height of any city from mean sea level.

    Adjusting gravitation anomaly

    • But there is one additional problem to be contended with — gravity. Gravity is different in different places. It means that even sea level cannot be considered to be uniform at all places.
    • So, the local gravity is also measured to calculate the local sea level. Nowadays sophisticated portable gravitometers are available that can be carried even to mountain peaks.

    Technology solutions

    • These days GPS is widely used to determine coordinates and heights, even of mountains.
    • But, GPS gives precise coordinates of the top of a mountain relative to an ellipsoid which is an imaginary surface mathematically modelled to represent Earth.
    • This surface differs from the mean sea level. Similarly, overhead flying planes equipped with laser beams (LiDAR) can also be used to get the coordinates.

    How accurate are China/Nepal’s apprehensions?

    • Considering that during 1952-1954, when neither GPS and satellite techniques were available nor the sophisticated gravimeters, the task of determining the height of Mount Everest was not easy.
    • Nepal and China have said they have measured Mount Everest to be 86 cm higher than the 8,848 m that it was known to be.
    • But these have been explained in terms of geological processes that might be altering the height of Everest. The accuracy of the 1954 result has never been questioned.
    • Most scientists now believe that the height of Mount Everest is increasing at a very slow rate. This is because of the northward movement of the Indian tectonic plate that is pushing the surface up.
    • Big earthquake, like the one that happened in Nepal in 2015, can alter the heights of mountains. Such events have happened in the past.

  • What are Rossby Waves?

    Droughts in India have historically been associated with El Nino, anomalous warming of the equatorial Pacific, but Indian scientists have found some relevance in Rossby Waves.

    Q.The determinants of Indian Monsoon are no more limited to the Pacific and the Indian Ocean. Discuss.

    El-Nino alone do not cause drought

    • The study says that nearly six out of 10 droughts, in non-El Nino years occurred during the Indian summer-monsoon season in the past century.
    • They may have been driven by atmospheric disturbances from the North Atlantic region.
    • In an El Niño year, abnormally warm equatorial Pacific waters pull moisture-laden clouds away from the subcontinent.
    • But the IISc Bangalore study shows that in non-El Nino years, these droughts are a consequence of a sudden and steep drop in rainfall in late August.

    Then, how were droughts induced?

    • In an El Nino year, the rainfall deficit departure from a long-term average set in early around mid-June and progressively worsen.
    • Researchers tried to trace this drought back to a forcing agent or system that influences the behaviour over India.
    • They found, the winds that were prevalent in these non-El Niño drought years.

    Another factor: The Rossby Waves

    • The researchers noted that winds in the upper atmosphere are interacting with a deep cyclonic circulation above the abnormally cold North Atlantic waters.
    • The resulting wave of air currents called a Rossby wave, curved down from the North Atlantic squeezed in by the Tibetan plateau and hits the subcontinent around mid-August.
    • This has a suppressing effect on rainfall and throws off the monsoon that was trying to recover from the June slump.

    Now scratch your basics on Planetary Winds. “Go back to the NCERTs !”

    What are Rossby Waves?

    • They are giant meanders in high-altitude winds that have a major influence on the weather.
    • They are influenced by the Coriolis force and pressure gradient.
    • The wave’s usual course is to go from west to east, but not towards the equator.

    Points to be noted ……

    • The Indian Ocean and the Pacific Ocean seem to be at the forefront of all discussions surrounding Indian monsoon droughts.
    • Thus beyond looking at the Pacific Ocean it is important to consider other influences on the Indian monsoon from outside the tropics.
    • It is perhaps time to focus just as much on mid-latitude influences, which might aid in getting a better handle on enhanced predictability of monsoon variability.

  • What is Aurora Borealis?

    Northern Lights, also known as aurora borealis could be visible in regions such as in the northern parts of Illinois and Pennsylvania in the US.

    Try this PYQ:

    What is a coma, in the context of Astronomy?

    (a) Bright half of material on the comet

    (b) Long tail of dust

    (c) Two asteroids orbiting each other

    (d) Two planets orbiting each other

    Aurora

    • Auroras occur when charged particles ejected from the Sun’s surface — called the solar wind — enter the Earth’s atmosphere.
    • While flowing toward Earth, the fast-moving solar wind carries with it the Sun’s magnetic field, which disrupts the magnetosphere — the region of space around Earth in which the magnetic field of our planet is dominant.
    • When the Sun’s magnetic field approaches Earth, the protective magnetic field radiating from our planet’s poles deflects the former, thus shielding life on Earth.
    • However, as this happens, the protective fields couple together to form funnels, through which charged solar wind particles are able to stream down to the poles.
    • At the north and south poles, the charged particles interact with different gases in the atmosphere, causing a display of light in the sky.
    • This display, known as an aurora, is seen from the Earth’s high latitude regions (called the auroral oval), and is active all year round.

    Behind the name

    • In the northern part of our globe, the polar lights are called aurora borealis or Northern Lights and are seen from the US (Alaska), Canada, Iceland, Greenland, Norway, Sweden and Finland.
    • In the south, they are called aurora australis or southern lights and are visible from high latitudes in Antarctica, Chile, Argentina, New Zealand and Australia.

    Where is it observed?

    • Generally, the auroral oval is usually witnessed far up in the Polar Regions or the high latitude regions of Europe, like in Norway.
    • But occasionally, the oval expands, and the lights become visible at lower latitudes.
    • This happens during periods of high solar activity, such as the arrival of solar storms.
    • Solar activities include solar flares, solar energetic particles, high-speed solar wind and Coronal Mass Ejections (CME).

  • Revised height of Mount Everest

    Nepal and China jointly announced the new height of Mount Everest as 8,848.86 meters.

    8,848 metres — the answer to one of the most widely popular quiz questions, and a number drilled into the minds of school students around the world for decades, is set for a revision.

    Mt. Everest

    • Mount Everest or Sagarmatha, Earth’s highest mountain above sea level, is located in the Himalayas between China and Nepal -– the border between them running across its summit point.
    • Its current official elevation – 8,848.86m – places it more than 200m above the world’s second-highest mountain, K2, which is 8,611m tall and located in Pakistan-occupied Kashmir.
    • The mountain gets its English name from Sir George Everest, a colonial-era geographer who served as the Surveyor General of India in the mid-19th century.
    • Considered an elite climbing destination, Everest was first scaled in 1953 by the Indian-Nepalese Tenzing Norgay and New Zealander Edmund Hillary.

    Try this PYQ:

    Q.When you travel to the Himalayas, you will see the following:

    1. Deep gorges
    2. U-turn river courses
    3. Parallel mountain ranges
    4. Steep gradients causing land-sliding

    Which of the above can be said to be the evidences for the Himalayas being young fold mountains?

    (a) 1 and 2 only

    (b) 1, 2 and 4 only

    (c) 3 and 4 only

    (d) 1, 2, 3 and 4

    Everest’s first survey

    • The mission to measure the world’s highest peak was taken up on a serious note in 1847 and culminated with the finding of a team led by Andrew Waugh of the Royal Surveyor General of India.
    • The team discovered that ‘Peak 15’ — as Mt Everest was referred to then — was the highest mountain, contrary to the then-prevailing belief that Mt Kanchenjunga (8,582 m) was the highest peak in the world.
    • Another belief, prevailing even today, is that 8,840 m is not the height that was actually determined by the 19th-century team.
    • That survey, based on trigonometric calculations, is known as the Great Trigonometric Survey of India.

    Why is the height being revised?

    • The height of the summit, however, is known to change because of tectonic activity, such as the 2015 Nepal earthquake.
    • Its measurement over the decades has also depended on who was surveying.
    • Another debate is whether the height should be based on the highest rock point or the highest snow point.

  • Western Disturbances and winters in North

    For the past few days, Chandigarh and its neighbouring states have been experiencing unusually cold days although the night temperatures are normal.

    Try this PYQ:

    Consider the following statements:

    1. The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.
    2. The moist air masses that cause winter rains in the North-Western region of India are part of westerlies.

    Which of the statements given above is/are correct?

    (a) Only 1

    (b) Only 2

    (c) Both 1 and 2

    (d) Neither 1 nor 2

    Temperature anomaly in North

    • Meteorological officials have attributed the trend to the cloud cover in the region which was absent until a few days ago.
    • It is the result of a western disturbance, which has brought about a spell of precipitation in the northwest Himalaya.

    Role of clouds

    • During the day, clouds obstruct the heat from the sun from reaching the surface of the earth, reflecting some of it back into space.
    • This lowers the temperature. Cold winds blowing down from snow-bound areas in the mountains also contribute to the cooling effect.
    • At night, however, clouds act like blankets – they help retain some of the heat energy radiated back by the earth’s surface.
    • Overcast weather at night, thus, increases greenhouse warming.

    What are western disturbances?

    • In northern India, winter rains and clouds are generally caused by moisture-bearing wind systems called western disturbances.
    • They originate and gather moisture over the Mediterranean region and flow eastwards towards the Indian subcontinent.
    • When some of these winds run into mountains of the northwest Himalaya, they are forced upward.
    • At higher altitudes, the temperatures drop and water vapour gets condensed. This leads to cloud formation and eventually rain and snow.

    Other factors for severe winters in North

    • In north India, the huge temperature difference between summers and winters is due to its continentality (distance from seas and oceans).
    • Air from oceans moderates the temperature as it moves onshore, but this effect is missing in continental interiors.
    • As a result, north India has greater seasonal differences as compared to peninsular India.
    • Temperature also reduces rapidly with altitude, and thus, the Himalayan region is colder still.

  • Why has the Northeast Monsoon remained deficient this year?

    Rainfall over the Southern peninsular region has been deficient so far due to prevailing La Nina conditions according to the India Meteorological Department (IMD).

    Try this PYQ:

    Q.La Nina is suspected to have caused recent floods in Australia. How is La Nina different from El Nino?

    1. La Nina is characterized by unusually cold ocean temperature in equatorial Indian Ocean whereas El Nino is characterized by unusually warm ocean temperature in the equatorial Pacific Ocean.
    2. El Nino has an adverse effect on south-west monsoon of India, but La Nina has no effect on monsoon climate.

    Which of the statements given above is/are correct?

    (a) Only 1

    (b) Only 2

    (c) Both 1 and 2

    (d) Neither 1 nor 2

    What is the Northeast monsoon?

    • India receives rainfall during two seasons.
    • About 75 per cent of the country’s annual rainfall is received from the Southwest monsoon between June and September.
    • The Northeast monsoon, on the other hand, occurs from October to December and is a comparatively small-scale monsoon, which is confined to the Southern peninsula.
    • After the complete withdrawal of the Southwest monsoon from the country takes place by mid-October, the wind pattern rapidly changes from the south-westerly to the north-easterly direction.
    • Also called the winter monsoon, the rainfall associated with the Northeast monsoon is important for almost entire South India.

    Why it is important?

    • Tamil Nadu records about 48 per cent (447.4 mm) of its annual rainfall (943.7 mm) during these months, making it the key factor for undertaking agricultural activities and reservoir management in the state.
    • Some South Asian countries such as Maldives, Sri Lanka and Myanmar also record rainfall from October to December.

    Why there are distortions?

    • The majority of districts in Tamil Nadu remain highly rain-deficient up this time.
    • The period after the Southwest monsoon season, from October to December, is the peak time for cyclonic activity in the North Indian Ocean region — covering the Arabian Sea and the Bay of Bengal.
    • The winds associated with the formation of low-pressure systems, depressions, or cyclones influence this monsoon, and therefore, the rainfall.
    • Officials at IMD have linked it to the prevailing La Niña conditions in the Pacific Ocean.

    La Nina  link with the NE monsoon

    • While La Niña conditions enhance the rainfall associated with the Southwest monsoon, it has a negative impact on rainfall associated with the Northeast monsoon.
    • During La Niña years, the synoptic systems — low pressure or cyclones — formed in the Bay of Bengal remain significantly to the north of their normal position.
    • Besides, instead of moving westwards, these systems recurve. As they lie to the north of their normal position, not much rainfall occurs over southern regions like Tamil Nadu.

    Back2Basics: El Nino and La Nina

    • While El Niño (Spanish for ‘little boy’), the more common expression, is the abnormal surface warming observed along the eastern and central regions of the Pacific Ocean (the region between Peru and Papua New Guinea).
    • The La Niña (Spanish for ‘little girl’) is an abnormal cooling of these surface waters.
    • Together, the El Niño and La Niña phenomena are termed as El Niño Southern Oscillation (ENSO).
    • These are large-scale ocean phenomena which influence the global weather — winds, temperature and rainfall. They have the ability to trigger extreme weather events like droughts, floods, hot and cold conditions, globally.
    • Each cycle can last anywhere between 9 to 12 months, at times extendable to 18 months — and re-occur after every three to five years.
    • Meteorologists record the sea surface temperatures for four different regions, known as Niño regions, along this equatorial belt.
    • Depending on the temperatures, they forecast either as an El Niño, an ENSO neutral phase, or a La Niña.

  • Cyclone Nivar to make landfall in TN

    A developing cyclonic disturbance in the Bay of Bengal is expected to become a ‘severe cyclonic storm’ and make landfall in Tamil Nadu.

    Cyclone Nivar

    • The IMD has forecasted the development of a cyclone in the Southwest region of the Bay of Bengal, off Tamil Nadu coast.
    • It has said that it will strengthen into a cyclone. Once intensified, it would acquire its name ‘Nivar’, proposed by Iran.
    • After cyclone Gaja in 2018, this will be the second cyclone to cross Tamil Nadu in the last two years.

    Try this PYQ:

    In the South Atlantic and South-Eastern Pacific regions in tropical latitudes, cyclone does not originate. What is the reason?

    (a) Sea surface temperatures are low

    (b) Inter-Tropical Convergence Zone seldom occurs

    (c) Coriolis force is too weak

    (d) Absence of land in those regions

    Tropical Cyclone

    • A Tropical cyclone is an intense circular storm that originates over warm tropical oceans and is characterized by low atmospheric pressure, high winds, and heavy rain.
    • Cyclones are formed over slightly warm ocean waters. The temperature of the top layer of the sea, up to a depth of about 60 meters, need to be at least 28°C to support the formation of a cyclone.
    • This explains why the April-May and October-December periods are conducive for cyclones.
    • Then, the low level of air above the waters needs to have an ‘anticlockwise’ rotation (in the northern hemisphere; clockwise in the southern hemisphere).
    • During these periods, there is an ITCZ in the Bay of Bengal whose southern boundary experiences winds from west to east, while the northern boundary has winds flowing east to west.
    • Once formed, cyclones in this area usually move northwest. As it travels over the sea, the cyclone gathers more moist air from the warm sea which adds to its heft.

    Must read:

    [Burning Issue] Tropical Cyclones and India