EARTH OBSERVATION SATELLITES (EOS)

- Earth observation satellites, also known as Earth remote sensing satellites, are designed to monitor and collect data about the Earth from orbit. This category includes both military spy satellites and those intended for non-military purposes, such as environmental monitoring, weather forecasting, cartography, and more.
- These satellites are crucial for overseeing and safeguarding our environment, managing resources, responding to global humanitarian crises, and supporting sustainable development. They offer valuable insights into various aspects like ocean salinity, ice thickness, crop health, and air quality.
- The most common type of Earth observation satellites are Earth-imaging satellites, which capture images similar to aerial photographs. However, some EO satellites conduct remote sensing without creating images, such as those using GNSS radio occultation techniques
3.Types of Earth Observation Satellites
Earth observation satellites are crucial tools for monitoring our planet. They provide valuable data for various applications, including weather forecasting, environmental monitoring, and disaster management
Earth observation (EO) satellites can be categorized into two main types depending on their imaging techniques: passive and active.
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Passive Satellites: These satellites detect radiation that is reflected off the Earth's surface, including visible light and infrared. They generally cannot operate effectively through cloud cover.
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Active Satellites: These satellites emit energy towards the Earth's surface and measure the reflected signal to gather information. They are capable of penetrating cloud cover to obtain data
- Earth observation satellites operate in various orbits, providing different viewpoints of the Earth. Due to constraints in power and storage, most satellites do not continuously collect data.
- Some satellites provide consistent and reliable data, while others gather it intermittently over time.
- The collected data is stored on the satellite until it can be transmitted to a ground station when it comes into view.
- The duration from image capture to data availability can range from a month to just a few minutes, with advancements in technology reducing this time.
- As multiple companies own these satellites, there are various data providers with distinct pricing models.
- ISRO has deployed numerous operational remote sensing satellites. Currently, thirteen of these satellites are in sun-synchronous orbits, while four are in geostationary orbits.
- The data collected from these satellites supports a range of applications including agriculture, water resources, urban planning, rural development, mineral exploration, environmental monitoring, forestry, ocean resource management, and disaster response
- Climate Change: Track changes in climate patterns, ice melt, sea level rise, and greenhouse gas concentrations.
- Natural Disasters: Monitor and assess the impact of natural disasters like hurricanes, earthquakes, and floods in real-time.
- Agriculture: Provide data on crop health, soil conditions, and irrigation needs, helping optimize agricultural practices and increase yields.
- Water Resources: Monitor water bodies, track changes in water availability, and manage water resources more effectively.
- Land Use: Assist in urban planning and land use management by providing detailed imagery and data on land development and changes.
- Infrastructure: Support infrastructure development by providing accurate and up-to-date information on land and environmental conditions
For Prelims: LOS, PSLV, GSLV
For Mains: GS III - Science & technology
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Previous Year Questions
1. With reference to India's satellite launch vehicles, consider the following statements: (UPSC 2018)
1. PSLVs launch satellites useful for Earth resources monitoring whereas GSLVs are designed mainly to launch communication satellites.
2. Satellites launched by PSLV appear to remain permanently fixed in the same position in the sky, as viewed from a particular location on Earth.
3. GSLV Mk III is a four- staged launch vehicle with the first and third stages using solid rocket motors; and the second and fourth stages using liquid rocket engines.
Which of the statements given above is/are correct?
A. 1 only
B. 2 and 3
C. 1 and 2
D. 3 only
Answer: A
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KEELADI
1. Context
2. How Keeladi linked to sangam age?
- The Sangam age is a period of history in ancient Tamil Nadu that was believed to be from the third century BCE to the third century CE.
- Excavations by the Archaeological Survey of India (ASI) and Tamil Nadu State Archaeology Department (TNSDA) had pushed the Sangam age further back.
- In 2019, a TNSDA report dated the unearthed artifacts from Keeladi to a period between the sixth century BCE and the first century BCE. One of the six samples collected at a depth of 353 cm, sent for carbon dating in the U.S., dated back to 580 BCE.
- The findings in the TNSDA report placed Keeladi artifacts about 300 years earlier than the previously believed third century BCE.
- Keeladi could also provide crucial evidence for understanding the missing links of the Iron Age (12th century BCE to sixth century BCE) to the Early Historic Period (sixth century BCE to fourth century BCE) and subsequent cultural developments.
3. Links to Indus Valley Civilisation
- The unearthed Keeladi artifacts have led academics to describe the site as part of the Vaigai Valley Civilisation.
- The findings have also invited comparisons with the Indus Valley Civilisation while acknowledging the cultural gap of 1,000 years between the two places.
- Till now, the gap is filled with Iron Age material in south India, which serves as residual links. However, some of the symbols found in pot sherds of Keeladi bear a close resemblance to Indus Valley signs.
- A lot of digging and study has to be done to establish the links between these two civilizations.
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4. About Sangam Age
- The word ‘Sangam’ is the Tamil form of the Sanskrit word Sangha which means a group of persons or an association.
- The Tamil Sangam was an academy of poets who flourished in three different periods and in different places under the patronage of the Pandyan kings.
- The Sangam literature, largely consolidated from the third Sangam, throws information on the conditions of life of people around the beginning of the Christian era.
- It deals with the secular matter relating to public and social activities like government, war charity, trade, worship, agriculture, etc.
- Sangam literature consists of the earliest Tamil works (such as the Tolkappiyam), the ten poems (Pattupattu), the eight anthologies (Ettutogai) and the eighteen minor works (Padinenkilkanakku), and the three epics.
5. About Vaigai River
- It is an east-flowing river.
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The Vaigai river basin is an important one among the 12 basins between the Cauvery and Kanyakumari.
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This basin is bounded by the Cardamom Hills and the Palani Hills on the West and by the Palk Strait and Palk Bay on the East.
6. What has been unearthed so far?
- In the eight rounds of excavations, including the first three by the ASI, over 18,000 artifacts have been unearthed from the site and the unique artifacts will be on display at the museum to the opened soon.
- The unearthing of heaps of pottery suggests the existence of a pottery-making industry, mostly made of locally available raw materials. Over 120 potsherds containing Tamil Brahmi inscriptions have been found.
- Keeladi, along with other Tamil Nadu sites which have over a thousand inscribed potsherds, clearly suggest the long survival of the script.
- Gold ornaments, copper articles, semi-precious stones, shell bangles, ivory bangles, and ivory combs reflect the artistic, culturally rich, and prosperous lifestyle of the Keeladi people.
- Agate and carnelian beads suggest import through commercial networks while terracotta and ivory dice, gamesmen, and evidence of hopscotch have been unearthed revealing their pastime hobbies.
Rakhigarhi Excavation and Discoveries:
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While excavation continues at the ancient Harappan site of Rakhigarhi in Haryana’s Hisar district, situated along the Ghaggar-Hakra river plain, the central government has granted protected status to the mounds under the Ancient Monuments and Archaeological Sites and Remains Act of 1958.
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Rakhigarhi ranks among the two most prominent Harappan sites in India, alongside Dholavira in Gujarat.
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During a three-month excavation in 2022 at three of Rakhigarhi’s seven mounds, archaeologists uncovered remnants of residential structures, streets, a drainage network, and a possible jewelry-making workshop. The dig also yielded artifacts such as copper and gold ornaments, terracotta figurines, seals, and numerous pottery pieces.
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The initial excavation at the site was led by Amarendra Nath of the Archaeological Survey of India. Previously, Mohenjodaro in Pakistan was considered the largest Harappan city, but new excavations by Professor Vasant Shinde and his team at Rakhigarhi challenged that view.
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The discoveries point to both the early and mature phases of Harappan civilization at the site, which is believed to be around 5,000 years old. Notably, a cylindrical seal bearing five Harappan symbols on one side and an alligator motif on the other was found.
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Ritual practices are evidenced by findings such as a sacrificial pit constructed with mud bricks and fire altars in triangular and circular shapes. A DNA analysis of human remains from the Rakhigarhi cemetery indicates the Harappans had an indigenous origin, contradicting earlier theories linking them to steppe or ancient Iranian populations.
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Rakhigarhi also provided the first recorded instance of a double burial, featuring the remains of a male and a female (aged approximately 38 and 25, respectively).
Ratnagiri Buddhist Site Excavations:
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Excavation at the Buddhist complex in Ratnagiri, dating from the 5th to 13th centuries, has revealed significant artifacts including a large Buddha head, a massive hand, an ancient boundary wall, and inscribed relics, believed to date back to the 8th and 9th centuries AD. These discoveries reaffirm Ratnagiri’s importance as a Buddhist heritage site in Odisha’s Jajpur district.
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Debala Mitra, who later became the ASI’s first woman Director General (1981–83), led the site’s initial excavation between 1958 and 1961. Afterward, no further large-scale excavations occurred, even though visible structures and statues hinted at untapped potential. Focus shifted instead to other Buddhist sites in Odisha.
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Ratnagiri, meaning "Hill of Jewels," is located about 100 km northeast of Bhubaneswar, on elevated terrain between the Birupa and Brahmani rivers. It is the most renowned and extensively explored Buddhist site in the state.
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Together with Udaygiri and Lalitgiri, Ratnagiri forms the celebrated ‘Diamond Triangle’ of Odisha, with all three sites clustered in the Jajpur and Cuttack districts.
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Ratnagiri is considered a key early hub of Vajrayana or Tantrayana Buddhism, a tradition that emphasized achieving spiritual power through practices associated with the Vajra (thunderbolt or diamond). This belief is the basis for the ‘Diamond Triangle’ nomenclature.
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Unique among Indian Buddhist monasteries, Ratnagiri's monastery features a curvilinear roof. Historical records suggest that at its height, the site accommodated around 500 monks who practiced the Tantrayana tradition of Buddhism
For Prelims: Keeladi, Sangam age of Tamil Nadu, Archaeological Survey of India (ASI) and Tamil Nadu State Archaeology Department (TNSDA), Vaigai Valley Civilisation, Indus Valley Civilisation, Iron Age, Tolkappiyam, Pattupattu, Ettutogai, Padinenkilkanakku, Cardamom Hills, Palani Hills, and Vaigai River. |
Previous year question1.Which one of the following statements about Sangam literature in ancient South India is correct? (UPSC 2022)
A. Sangam poems are devoid of any reference to material culture.
B. The social classification of Varna was known to Sangam poets.
C. Sangam poems have no reference to the warrior ethic.
D. Sangam literature refers to magical forces as irrational.
Answer: B
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GROSS DOMESTIC PRODUCT (GDP)
There are three primary ways to calculate GDP:
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Production Approach (GDP by Production): This approach calculates GDP by adding up the value-added at each stage of production. It involves summing up the value of all final goods and services produced in an economy.
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Income Approach (GDP by Income): This approach calculates GDP by summing up all the incomes earned in an economy, including wages, rents, interests, and profits. The idea is that all the income generated in an economy must ultimately be spent on purchasing goods and services.
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Expenditure Approach (GDP by Expenditure): This approach calculates GDP by summing up all the expenditures made on final goods and services. It includes consumption by households, investments by businesses, government spending, and net exports (exports minus imports).
3. Measuring GDP
GDP can be measured in three different ways:
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Nominal GDP: This is the raw GDP figure without adjusting for inflation. It reflects the total value of goods and services produced at current prices.
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Real GDP: Real GDP adjusts the nominal GDP for inflation, allowing for a more accurate comparison of economic performance over time. It represents the value of goods and services produced using constant prices from a specific base year.
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GDP per capita: This is the GDP divided by the population of a country. It provides a per-person measure of economic output and can be useful for comparing the relative economic well-being of different countries.
The GDP is a useful measure of economic health, but it has some limitations. For example, it does not take into account the distribution of income in an economy. It also does not take into account the quality of goods and services produced.
Despite its limitations, the GDP is a widely used measure of economic health. It is used by economists, policymakers, and businesses to track the performance of an economy and to make decisions about economic policy
4. Gross Value Added (GVA)
Gross Value Added (GVA) is a closely related concept to Gross Domestic Product (GDP) and is used to measure the economic value generated by various economic activities within a country. GVA represents the value of goods and services produced in an economy minus the value of inputs (such as raw materials and intermediate goods) used in production. It's a way to measure the contribution of each individual sector or industry to the overall economy.
GVA can be calculated using the production approach, similar to one of the methods used to calculate GDP. The formula for calculating GVA is as follows:
GVA = Output Value - Intermediate Consumption
Where:
- Output Value: The total value of goods and services produced by an industry or sector.
- Intermediate Consumption: The value of inputs used in the production process, including raw materials, energy, and other intermediate goods.
Gross Domestic Product (GDP) and Gross National Product (GNP) are both important economic indicators used to measure the size and health of an economy, but they focus on slightly different aspects of economic activity and include different factors. Here are the key differences between GDP and GNP:
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Definition and Scope:
- GDP: GDP measures the total value of all goods and services produced within a country's borders, regardless of whether the production is done by domestic or foreign entities. It only considers economic activities that take place within the country.
- GNP: GNP measures the total value of all goods and services produced by a country's residents, whether they are located within the country's borders or abroad. It takes into account the production of residents, both domestically and internationally.
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Foreign Income and Payments:
- GDP: GDP does not consider the income earned by residents of a country from their economic activities abroad, nor does it account for payments made to foreigners working within the country.
- GNP: GNP includes the income earned by a country's residents from their investments and activities abroad, minus the income earned by foreign residents from their investments within the country.
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Net Factor Income from Abroad:
- GDP: GDP does not account for net factor income from abroad, which is the difference between income earned by domestic residents abroad and income earned by foreign residents domestically.
- GNP: GNP includes net factor income from abroad as part of its calculation.
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Foreign Direct Investment:
- GDP: GDP does not directly consider foreign direct investment (FDI) flowing into or out of a country.
- GNP: GNP considers the impact of FDI on the income of a country's residents, both from investments made within the country and from investments made by residents abroad.
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Measurement Approach:
- GDP: GDP can be calculated using three different approaches: production, income, and expenditure approaches.
- GNP: GNP is primarily calculated using the income approach, as it focuses on the income earned by residents from their economic activities.
For Prelims: GDP, GVA, FDI, GNP
For Mains: 1.Discuss the recent trends and challenges in India's GDP growth
2.Examine the role of the service sector in India's GDP growth
3.Compare and contrast the growth trajectories of India's GDP and GNP
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Previous Year Questions
1.With reference to Indian economy, consider the following statements: (UPSC CSE, 2015)
1. The rate of growth of Real Gross Domestic Product has steadily increased in the last decade. 2. The Gross Domestic Product at market prices (in rupees) has steadily increased in the last decade. Which of the statements given above is/are correct? (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Answer (b)
2.A decrease in tax to GDP ratio of a country indicates which of the following? (UPSC CSE, 2015) 1. Slowing economic growth rate 2. Less equitable distribution of national income Select the correct answer using the code given below: (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2 Answer (a)
Previous year UPSC Mains Question Covering similar theme: Define potential GDP and explain its determinants. What are the factors that have been inhibiting India from realizing its potential GDP? (UPSC CSE GS3, 2020) Explain the difference between computing methodology of India’s Gross Domestic Product (GDP) before the year 2015 and after the year 2015. (UPSC CSE GS3, 2021) |
BRAHMAPUTRA RIVER AND CHINA'S BRIDGE
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- Chinese Premier Li Qiang has formally inaugurated the construction of a massive hydropower dam in Nyingchi City, situated in the Tibet Autonomous Region along the lower course of the Brahmaputra River, which is locally called the Yarlung Zangbo.
- This significant move, reported by China’s state-run media, signals the beginning of a strategically and environmentally impactful project in a region of geopolitical sensitivity, particularly due to its proximity to India’s northeastern border.
- The project is being described as one of the largest hydropower developments globally, both in scale and investment. It involves the construction of five cascade hydropower stations, a system designed to maximize energy output by building multiple dams along the river’s flow.
- The total estimated investment for the project is about 1.2 trillion Yuan (approximately USD 167.8 billion), underscoring China’s long-term commitment to clean energy infrastructure and regional development in Tibet.
- At present, China’s Three Gorges Dam on the Yangtze River holds the record as the world's largest dam, boasting an installed capacity of 22.5 gigawatts. However, the newly announced project is likely to surpass it in terms of complexity and strategic relevance.
- The chosen location near the dramatic "Great Bend" of the Yarlung Tsangpo is particularly favorable for hydropower generation.
- Here, the river plunges about 2,000 meters within a short distance of 50 kilometers, offering immense potential for energy extraction through gravitational force.
- This development has broader implications beyond energy. It may influence water flow into the Brahmaputra basin, a lifeline for millions in India and Bangladesh, prompting concerns over transboundary river management and ecological impacts.
- While China insists the project is purely for energy purposes, its location in a seismically active and environmentally fragile zone continues to raise international attention and calls for cooperative water governance among the riparian nations
- The proposed Chinese dam is strategically located near the sharp U-turn of the Brahmaputra River—an area often referred to as the “Great Bend”—where the river dramatically curves before entering India’s Arunachal Pradesh and later flowing into Bangladesh, where it is known as the Jamuna.
- This particular stretch is not only geographically significant but also hydrologically sensitive. Alterations in the river’s natural flow at this point could disrupt the hydrological balance downstream, affecting water availability in both India and Bangladesh.
- Such disruptions may have serious consequences for the agricultural sector, which is heavily dependent on the seasonal flow of the Brahmaputra. Rice and jute cultivation, in particular, are highly water-sensitive, and changes in flow patterns could lead to reduced irrigation potential, crop failure, or delayed sowing seasons.
- Moreover, the river supports millions of livelihoods, especially in the Assam and Bangladesh floodplains, where fishing and farming are key economic activities.
- Environmental experts are also concerned about the dam's impact on the Eastern Himalayas, a globally recognized biodiversity hotspot. This region is home to countless endemic and endangered species, and changes in river ecology could disturb aquatic habitats, migratory routes, and forest ecosystems.
- Additionally, the area is prone to seismic activity, raising the risk of dam-related disasters such as landslides or reservoir-induced earthquakes.
- While China underscores the importance of this mega-project as a vital component of its renewable energy strategy—intended to reduce carbon emissions and promote sustainable development—it has not entered into any formal water-sharing treaty with India or Bangladesh.
- As a result, India and Bangladesh, being lower riparian states, are especially vulnerable to unilateral upstream activities. The absence of a transparent and cooperative water management framework raises geopolitical tensions, as such projects could be used to exert strategic leverage or cause ecological stress during droughts or conflicts.
- Given the transboundary nature of the Brahmaputra, many experts advocate for enhanced regional cooperation, joint river basin management, and early warning systems to ensure that hydropower development does not come at the cost of ecological and social stability across South Asia

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The Brahmaputra River is an international river system, with its basin covering an area of approximately 5,80,000 square kilometers. This vast catchment spans across four countries: China accounts for the largest share at 50.5%, followed by India with 33.3%, Bangladesh with 8.1%, and Bhutan contributing 7.8%.
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Within India, the Brahmaputra basin occupies about 1,94,413 square kilometers, making up roughly 5.9% of the nation’s total land area. The basin extends over several northeastern and eastern states including Arunachal Pradesh, Assam, Meghalaya, Nagaland, Sikkim, and West Bengal.
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The river has its source at the Chemayungdung Glacier, situated to the east of Mansarovar Lake in the Kailash mountain range in Tibet. In Tibet, it is known as the Yarlung Tsangpo, and it flows eastward for nearly 1,200 kilometers before curving southward.
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Near Namcha Barwa, the river takes a dramatic U-shaped turn—often referred to as the Great Bend—and enters India via Arunachal Pradesh, just west of Sadiya town. Here, the river is called the Siang or Dihang.
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As it flows southwest, the Siang is joined on the left bank by major tributaries such as the Dibang and Lohit, after which it takes the name Brahmaputra.
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On its right bank, the river receives important tributaries like the Subansiri (an antecedent river), Kameng, Manas, and Sankosh. The Brahmaputra continues its journey into the Bangladesh plains near Dhubri in Assam, eventually flowing southward.
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In Bangladesh, after the Teesta River merges from the right bank, the Brahmaputra is referred to as the Jamuna. It later converges with the Padma River, and the combined flow drains into the Bay of Bengal.
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All tributaries of the Brahmaputra within Indian territory are rain-fed, receiving intense rainfall during the southwest monsoon. This makes the region highly prone to seasonal flooding, riverbank erosion, and shifting of river channels, particularly in Assam.
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The river’s topography also makes it ideal for hydropower generation. In its Tibetan course of about 1,700 kilometers, the Brahmaputra descends nearly 4,800 meters, averaging a slope of 2.82 meters per kilometer. However, this gradient decreases drastically to 0.1 meter per kilometer once the river enters the Assam Valley, resulting in slower flow and increased sedimentation
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According to Ashok Kantha, former Indian Ambassador to China, India and China have established a broad-based Memorandum of Understanding (MoU) to facilitate cooperation on transboundary rivers, along with two separate agreements specifically addressing the Brahmaputra and Sutlej rivers.
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The MoU concerning the Sutlej was prompted by the Parechu incident, which had highlighted the need for consistent hydrological data sharing. However, China did not agree to provide year-round data, and the agreement has since expired and awaits renewal.
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The MoU on the Brahmaputra, which is designed to be renewed every five years, expired in 2023. According to the Jal Shakti Ministry, the renewal process is underway through official diplomatic exchanges.
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The broader umbrella agreement, signed in 2013, remains in force as it has no expiration clause. Despite this, the Ministry’s website notes that no active cooperation is currently taking place under this framework. Additionally, an Expert Level Mechanism established in 2006—intended to support annual bilateral meetings—has experienced periodic disruptions.
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In light of these limited cooperative structures, the 1997 United Nations Convention on the Law of the Non-Navigational Uses of International Watercourses is seen as a potential guiding framework for equitable and sustainable management of shared water resources between nations
For Prelims: UN Convention on the Law of the Non-Navigational Uses of International Watercourses (1997), Transboundary River Agreements
For Mains: GS Paper II: International Relations
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Related Question
1.The Brahmaputra River is known as “Yarlung Tsangpo” in which of the following countries?
A) India B) China C) Bhutan D) Bangladesh Answer: B) China |
NISAR
1. Context
2. Necessity of NISAR
- NISAR marks a significant milestone as the first large-scale Earth observation mission to use dual-frequency radar technology.
- This capability enables it to detect ground changes with unmatched precision, regardless of whether it's day or night, and in all weather conditions—including through clouds, smoke, or dense vegetation.
- Weighing about three tonnes and costing over $1.5 billion, NISAR ranks among the most expensive Earth-monitoring satellites ever launched.
- The Earth’s landscape is constantly undergoing transformation due to natural phenomena, human interventions, and climate variations. Observing these changes from space provides essential insights for scientists, policymakers, and emergency response teams.
- In response to this need, NASA and ISRO have joined forces on a mission that not only serves global monitoring goals but also ensures ISRO has reliable access to high-resolution data customized for Indian requirements.
- The mission targets six key scientific and practical domains: geophysical processes of the solid Earth, ecosystem dynamics, glacial and ice-sheet monitoring, coastal and marine systems, disaster management, and a variety of other applications such as monitoring groundwater levels, oil deposits, and infrastructure like dams and levees.
- Although the mission is officially planned to last three years, it has been engineered for a minimum lifespan of five years. Importantly, its open-data policy ensures that most of the data captured by NISAR will be made publicly available within hours of collection
3. How does NISAR work?
- Once launched, NISAR will be positioned in a sun-synchronous polar orbit, circling the Earth at an altitude of 747 kilometers with an orbital inclination of 98.4º. Unlike conventional satellites that capture images, NISAR will utilize synthetic aperture radar (SAR) technology, which sends radar pulses toward the Earth's surface and then measures the return time and phase shift of the reflected signals.
- The resolution of radar imaging improves with larger antenna sizes—known as aperture—but deploying physically large antennas in space is unfeasible. SAR overcomes this limitation by simulating a large antenna.
- As the satellite advances in its orbit, it emits repeated radar pulses and collects their echoes, which are later processed to reconstruct an image as if a giant antenna had captured them all at once—thus earning the term "synthetic aperture."
- NISAR will feature two radar systems: an L-band SAR operating at 1.257 GHz that penetrates vegetation and soil layers to detect subsurface changes and land deformations, and an S-band SAR at 3.2 GHz designed for observing finer surface details such as vegetation types and water bodies.
- Globally, the satellite will mainly operate using the L-band radar, which aligns with NASA’s scientific objectives. However, over India, ISRO will routinely utilize the S-band radar for targeted observations.
- These S-band acquisitions are tailored to India's specific needs, such as biomass estimation, soil moisture monitoring, and filtering out ionospheric interference, which are crucial for sectors like agriculture, forestry, and disaster response.
- Both space agencies aim to coordinate radar operations efficiently so that simultaneous use of both radars is possible over the Indian subcontinent, reducing data conflicts.
- In radar systems, polarisation refers to the orientation of the electric field in the radar wave. SAR can both send and receive horizontally or vertically polarised signals. Using various combinations of these allows NISAR to distinguish between different surface compositions such as snow, soil, crops, or forests.
- NISAR’s radar system will cover a wide area with a swath width of 240 km, thanks to a SweepSAR design. This approach uses a beam transmission system that, upon signal return, employs multiple smaller apertures that steer electronically to create scanning beams sweeping across the satellite’s ground path.
- This scan-on-receive method enables large-area coverage without sacrificing image clarity.
- The mission will deliver spatial resolutions ranging from 3 to 10 meters and vertical accuracy down to a few centimeters. This high level of detail is suitable for tracking urban land subsidence or other subtle ground movements. Each point on the Earth’s surface will be revisited every 12 days.
- NISAR is equipped with a massive 12-meter-wide mesh reflector antenna, enabling it to generate annual biomass maps at a resolution of 1 hectare and quarterly maps distinguishing between cultivated and fallow farmland.
- It will also provide detailed floodplain maps and, in emergencies, can generate ‘damage proxy maps’ within five hours of data capture.
- However, there are some limitations. Due to the satellite’s orbital geometry, certain data acquisition modes may not achieve full global coverage. At latitudes above 60º, NISAR will skip every other observation due to overlapping orbits.
- Furthermore, around 10% of Earth’s surface may not be covered from both ascending and descending passes within a given 12-day cycle
Another important component of the satellite is its large 39-foot stationary antenna reflector.
Made of a gold-plated wire mesh, the reflector will be used to focus " the radar signals emitted and received by the upward-facing feed on the instrument structure".
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- When NASA and ISRO agreed to collaborate on the NISAR project, both agencies committed to contributing equally in terms of funding, technology, and expertise.
- ISRO was responsible for providing the I-3K satellite bus — the core spacecraft framework that handles system commands, propulsion, orientation, and includes solar panels capable of generating 4 kW of power.
- In addition, ISRO delivered the complete S-band radar electronics system, a high-speed Ka-band communication unit, and a steerable high-gain antenna. The development of the S-band radar components was carried out at the Space Applications Centre in Ahmedabad.
- On the other hand, NASA’s primary input was the L-band synthetic aperture radar system. This was developed at the Jet Propulsion Laboratory (JPL), which supplied all related radio-frequency components, a 12-meter radar antenna, a 9-meter carbon fiber boom, and the structural assembly that supports both radar units.
- NASA also provided the L-band feed array and avionics systems, including a solid-state recorder with large data capacity, a GPS system, autonomous data management tools, and a Ka-band communication unit.
- After integration of the radar payloads at JPL, the spacecraft was sent to ISRO’s Satellite Centre in Bengaluru for final assembly. Once fully tested, NISAR will be launched aboard ISRO’s GSLV Mk-II rocket from the spaceport in Sriharikota, with ISRO overseeing the entire launch sequence.
- While the overall mission will be coordinated through NASA's Mission Operations Center at JPL, routine flight control and monitoring will be managed by ISRO’s Telemetry, Tracking and Command Network (ISTRAC) in Bengaluru.
- After deployment into orbit, the bulk of the mission’s data—approximately 3 terabytes daily—will be transmitted through NASA’s Near Earth Network ground stations located in Alaska, Norway’s Svalbard, and Punta Arenas in Chile.
- These facilities will work in conjunction with ISRO’s data reception stations in Shadnagar and Antarctica. Once the raw data are received, India’s National Remote Sensing Centre (NRSC) will process and distribute mission outputs tailored for Indian applications, in a workflow that parallels NASA’s global data distribution system
5. The Mission
- Once launched into space, NISAR will observe subtle changes in Earth's surfaces, helping researchers better understand the causes and consequences of such phenomena.
- It will spot warning signs of natural disasters, such as volcanic eruptions, earthquakes and landslides.
- The satellite will also measure groundwater levels, track flow rates of glaciers and ice sheets and monitor the planet's forest and agricultural regions, which can improve our understanding of carbon exchange.
By using synthetic aperture radar (SAR), NISAR will produce high-resolution images.
SAR is capable of penetrating clouds and can collect data day and night regardless of the weather conditions. The instrument's imaging Swath the width of the strip of data collected along the length of the orbit track is greater than 150 miles (240 kilometres), which allows it to image the entire Earth in 12 days. |
- NISAR is expected to be launched in January 2024 from Satish Dhawan Space Centre into a near-polar orbit.
- The satellite will operate for a minimum of three years.
- NASA requires the L-band radar for its global science operations for at least three years.
- Meanwhile, ISRO will utilise the S-band radar for a minimum of five years.
For Prelims & Mains
For Prelims: NISAR (NASA-ISRO Synthetic Aperture Radar), Satish Dhawan Space Centre, Earth-observation satellite, Jet Propulsion Laboratory, L-band and S-band synthetic aperture radar, GPS, GSLV launch system and spacecraft,
For Mains:
1. What is NISAR and Explain its benefits (250 Words)
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SELF-HELP GROUPS (SHG)
1. Context
2. Self Help Groups (SHGs)
- Self Help Groups (SHGs) are community-based organizations formed by a small group of individuals, usually from the same socio-economic background, who come together to collectively address their common needs and aspirations.
- These groups play a significant role in empowering marginalized and economically disadvantaged individuals, especially women, by providing them with a platform to enhance their social, economic, and decision-making capabilities.
3. Key Features and Objectives
- Collective Strength: SHGs encourage individuals to pool their resources, skills, and knowledge to collectively address challenges and opportunities.
- Financial Inclusion: SHGs promote savings and credit activities, allowing members to accumulate funds for emergencies, livelihood initiatives, and income generation.
- Empowerment of Women: SHGs predominantly focus on women's empowerment, aiming to enhance their status, self-confidence, and participation in household and community decision-making.
- Social Cohesion: SHGs foster a sense of community, solidarity, and mutual support among members, contributing to social cohesion and collective development.
- Skill Development: SHGs often engage in skill-building activities, vocational training, and awareness programs to enhance members' livelihood opportunities.
4. Need for SHGs
- Poverty Alleviation: SHGs contribute to poverty reduction by promoting income-generating activities and small-scale enterprises among members. These initiatives empower individuals to generate additional sources of income and improve their standard of living.
- Women's Empowerment: SHGs predominantly focus on women's empowerment by providing them with a collective platform to enhance their decision-making abilities, self-confidence, and socio-economic status. This empowerment extends to their households and communities.
- Access to Credit: SHGs provide an alternative source of credit for members who may not have access to formal banks. This access to credit supports various needs, including emergencies, education, health expenses, and livelihood development.
- Entrepreneurship Promotion: SHGs promote entrepreneurial spirit by encouraging members to initiate and manage small-scale businesses. This contributes to local economic development and job creation.
- Women's Participation: By involving women in SHGs, gender norms, and stereotypes can be challenged, leading to increased participation in decision-making processes and more equitable distribution of resources.
5. Issues with SHGs
While Self Help Groups (SHGs) have proven to be effective in addressing various socio-economic challenges, they also face certain issues and challenges that can impact their functioning and overall impact. Some of the key issues with SHGs include:
- Inequitable Participation: Despite the focus on women's empowerment, SHGs sometimes face challenges in ensuring equal and meaningful participation of all members, particularly marginalized and socially excluded women.
- Dependency on External Support: Many SHGs rely heavily on external support for training, capacity-building, and financial assistance. This can hinder their long-term sustainability and self-reliance.
- Lack of Financial Literacy: Some SHG members may have a limited understanding of financial concepts and practices, making it difficult for them to effectively manage their savings and loans.
- Limited Market Linkages: While SHGs encourage income-generating activities, members often lack access to markets to sell their products or services, which can hinder their economic growth.
- Loan Default and Repayment Issues: In some cases, members struggle with loan repayment, leading to tensions within the group and potential disruptions in trust and collaboration.
6. Role of SHG in Women's Empowerment
The role of Self Help Groups (SHGs) in women's empowerment is significant and multifaceted. SHGs provide a platform that empowers women economically, socially, and personally, enabling them to enhance their status, decision-making abilities, and overall well-being. Here's an overview of the role of SHGs in women's empowerment:
Economic Empowerment:
- Financial Inclusion: SHGs provide women access to savings and credit facilities, enabling them to accumulate funds for emergencies and invest in income-generating activities.
- Income Generation: SHGs promote entrepreneurship and livelihood opportunities among women, helping them generate additional sources of income for their families.
- Asset Ownership: Through collective savings and loan activities, women can acquire assets such as land, livestock, and equipment, contributing to their economic independence.
Social Empowerment:
- Decision-Making: Participation in SHGs helps women develop confidence, leadership skills, and a voice in household and community decisions.
- Knowledge and Awareness: SHGs offer a platform for sharing information, learning about health, education, legal rights, and government programs, empowering women to make informed choices.
Personal Empowerment:
- Self-Confidence: Engaging in group activities and interacting with peers fosters self-confidence and self-esteem among women.
- Agency and Autonomy: Women gain a sense of agency over their lives, enabling them to assert their rights and negotiate with family members and external stakeholders.
Gender Equality:
- Changing Norms: SHGs challenge traditional gender norms and stereotypes by promoting women's participation in economic activities, decision-making, and leadership roles.
- Balanced Power Dynamics: Women's increased involvement in income generation and decision-making contributes to more equitable power dynamics within households.
Community Transformation:
- Ripple Effect: Empowered women within SHGs serve as role models, inspiring other women in the community to join and pursue their own empowerment journey.
- Poverty Alleviation: Economic empowerment through SHGs contributes to poverty reduction and overall community development.
7. Conclusion
For Prelims: Self-Help Groups (SHGs), Poverty Alleviation, Financial Inclusion, Women Empowerment, and Gender Equality.
For Mains: 1. Discuss the role and significance of Self Help Groups (SHGs) in empowering marginalized communities, particularly women, for socio-economic development in rural areas. (250 Words)
2. Analyse the challenges faced by SHGs in their functioning and sustainability, and suggest measures to enhance their effectiveness as vehicles for grassroots empowerment and poverty alleviation. (250 Words)
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Previous year Question1. Consider the following statements: (UPSC 2023)
1. The Self-Help Group (SHG) programme was originally initiated by the State Bank of India by providing microcredit to the financially deprived.
2. In an SHG, all members of a group take responsibility for a loan that an individual member takes.
3. The Regional Rural Banks and Scheduled Commercial Banks support SHGs.
How many of the above statements are correct?
A. Only one
B. Only two
C. All three
D. None
Answer: B
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H5N2
Symptoms of avian influenza in humans are similar to those of regular flu and can include: Fever, cough, sore throat, muscle aches, and severe respiratory distress in advanced cases.
- Type A viruses are classified based on two proteins on their surfaces – Hemagglutinin (HA) and Neuraminidase (NA). There are about 18 HA subtypes and 11 NA subtypes.
- Several combinations of these two proteins are possible e.g., H5N1, H7N2, H9N6, H17N10, H18N11, etc.
- All known subtypes of influenza A viruses can infect birds, except subtypes H17N10 and H18N11, which have only been found in bats.
- The most notable of these subtypes is H5N1, which has been responsible for numerous human infections and fatalities in the past.
The Mexico case serves as a reminder of the ongoing need for global health systems to remain alert to the threats posed by zoonotic diseases and to ensure rapid response mechanisms are in place to prevent widespread outbreaks.
For Prelims:
Avian influenza H5N2, Avian influenza H5N1, Bird Flu, Hemagglutinin (HA) and Neuraminidase (NA), influenza A viruses, Genomic surveillance, Pathogens, and Viruses.
For Mains:
1.Discuss the impact of the H5N2 Avian Influenza virus on public health. What measures can be implemented at national and international levels to mitigate the spread of avian influenza viruses and minimize their impact on both poultry production and human health?
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Previous Year Questions 1. H1N1 virus is sometimes mentioned in the news with reference to which one of the following diseases? (UPSC 2015) A. AIDS Answer: D 2. Consider the following statements : (UPSC 2010) 1. Every individual in the population is an equally susceptible host for Swine Flu. 2. Antibiotics have no role in the primary treatment of Swine Flu. 3. To prevent the future spread of Swine Flu in the epidemic area, the swine (pigs) must all be culled. Which of the statements given above is/are correct? A. 1 and 2 only B. 2 only C. 2 and 3 only D. 1, 2 and 3 Answer: A 3. Which of the following statements is/are correct? (UPSC 2013) 1. Viruses lack enzymes necessary for the generation of energy. 2. Viruses can be cultured in any synthetic medium. 3. Viruses are transmitted from one organism to another by biological vectors only. Select the correct answer using the codes given below. A. 1 only B. 2 and 3 only C. 1 and 3 only D. 1, 2 and 3 Answer: A 4. Which of the following statements is/are correct? Viruses can infect (UPSC 2016)
Select the correct answer using the code given below: (a) 1 and 2 only Ans: (d) |
GRASSLAND BIRD CENSUS

Among the significant findings was the identification of a breeding colony of the endangered Finn’s Weaver, a bird unique to the Brahmaputra floodplains. The study focused on ten priority species that are either globally threatened or endemic to this region:
Species Name | Scientific Name | IUCN Status |
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Bengal Florican | Houbaropsis bengalensis | Critically Endangered |
Swamp Francolin | Ortygornis gularis | Near Threatened |
Indian Grassbird | Graminicola bengalensis | Near Threatened |
Finn’s Weaver | Ploceus megarhynchus | Endangered |
Swamp Grass Babbler | Laticilla cinerascens | Endangered |
Jerdon’s Babbler | Chrysomma altirostre | Vulnerable |
Slender-billed Babbler | Argya longirostris | Vulnerable |
Black-breasted Parrotbill | Paradoxornis flavirostris | Vulnerable |
Marsh Babbler | Pellorneum palustre | Vulnerable |
Bristled Grassbird | Schoenicola striatus | Vulnerable |
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Grasslands, dominated by the Poaceae family which includes between 10,000 to 12,000 species, span large portions of the Earth's surface and support rich biodiversity. These ecosystems are typically found in regions with low to moderate rainfall, ranging from 600 to 1,500 mm annually.
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Often underestimated, grasslands are even more beneficial than forests in several ways. They deliver crucial ecosystem functions such as water and carbon storage, nutrient recycling, and climate regulation. Importantly, they also sustain both human agriculture and livestock, alongside wild herbivores — which in turn support carnivores by serving as their prey base.
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In India, grasslands cover nearly 25% of the country’s land area. These include diverse types such as the alpine meadows in the Himalayas, the chaurs at their base, the terai grasslands along the floodplains of the Ganga and Brahmaputra rivers, the floating phumdis of Manipur (home to the famous “dancing deer”), the dry savannas of central and western India, and the sholas in the Western Ghats.
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Globally, grasslands are known by various names depending on the region. The World Wide Fund for Nature (WWF) notes that they are referred to as ‘savannah’ in Africa, ‘cerrado’ in South America, ‘prairie’ in North America, ‘steppe’ in Central Asia, and ‘meadow’ in the United Kingdom.
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What makes grasslands unique is their resilience — they can continue to grow even after being grazed by animals. This quality allows them to support a diverse range of wildlife. For instance, Kaziranga and Manas host species like the one-horned rhinoceros and wild water buffalo in their moist grasslands, the terai supports swamp deer, and the rare Sangai deer flourishes on the floating islands of Loktak Lake in Manipur.
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Despite their importance, most of India’s grasslands — like its wetlands — lack formal protection. A UNCCD report released last year on rangeland degradation revealed that less than 5% of the country’s grasslands are in protected zones. Furthermore, India’s grassland area reduced significantly from 18 million hectares in 2005 to just 12 million hectares by 2015
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On July 29, Tuesday, authorities released the 2024 summary report titled ‘Status of Tigers in the Kaziranga Tiger Reserve’, based on the Phase IV monitoring efforts carried out across the Eastern Assam, Nagaon, and Biswanath Wildlife Divisions. This assessment was conducted under the directives of the National Tiger Conservation Authority (NTCA).
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The latest count recorded 148 tigers within the reserve — a notable increase from 104 in 2022, 99 in 2018, and 96 in 2014. According to Reserve Director Sonali Ghosh, this growth positions Kaziranga as having the third-highest tiger density globally, following Corbett Tiger Reserve in Uttarakhand and Bandipur Tiger Reserve in Karnataka.
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The monitoring exercise lasted 103 days and employed 293 pairs of camera traps spread over 1,307.49 square kilometres. These traps captured 4,011 tiger images from 242 different sites. Based on the unique stripe patterns on their right flanks, 148 adult tigers were identified — comprising 83 females, 55 males, and 10 whose gender could not be determined.
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While the increase in population is encouraging, the report also highlights ongoing threats to Kaziranga’s tigers, including habitat loss, conflicts with humans, and the impact of expanding agriculture and infrastructure around the reserve
- Kaziranga National Park holds immense ecological, cultural, and conservation significance in India and globally. Located in the floodplains of the Brahmaputra River in Assam, Kaziranga is celebrated for its remarkable biodiversity, particularly as the single largest habitat of the Indian one-horned rhinoceros.
- In fact, it is home to more than two-thirds of the world's population of this species, making it the cornerstone of rhino conservation in South Asia.
- Declared a UNESCO World Heritage Site in 1985, Kaziranga is not just a sanctuary for rhinos but also a thriving ecosystem that supports tigers, elephants, wild water buffalo, swamp deer, and numerous bird species.
- It is part of the Eastern Himalayan biodiversity hotspot and represents one of the last remaining undisturbed natural areas in the Brahmaputra Valley floodplain.
- What sets Kaziranga apart is its dynamic riverine ecosystem shaped by annual floods, which sustain its vast expanses of grasslands, wetlands, and forests. These natural cycles create ideal conditions for a diverse range of flora and fauna, particularly large herbivores. This, in turn, supports a healthy population of carnivores, including one of the highest tiger densities in the world.
- Kaziranga is also significant from a conservation policy perspective. It is one of the first protected areas in India to implement rigorous anti-poaching strategies and community engagement models. The park’s success in wildlife protection has become a case study in how conservation can be balanced with tourism and local livelihoods.
- Moreover, Kaziranga plays a vital role in climate regulation, water retention, and flood mitigation in the region. It acts as a natural buffer during the Brahmaputra’s monsoon overflow, absorbing excess water and reducing downstream damage. The park is also an important carbon sink, contributing to climate resilience in northeast India.
- In essence, Kaziranga is not just a wildlife reserve; it is a living landscape that reflects the intricate relationship between nature, people, and policy. Its continued protection is essential for maintaining ecological balance, conserving endangered species, and supporting the broader environmental and economic health of the region
- The National Tiger Conservation Authority (NTCA) is a statutory body under the Ministry of Environment, Forest and Climate Change (MoEFCC), Government of India. It was established in 2006 under the provisions of the Wildlife (Protection) Act, 1972, as amended by the Wildlife (Protection) Amendment Act, 2006
- The NTCA was created to strengthen tiger conservation efforts in India and to implement the Project Tiger program more effectively. Its formation followed concerns about declining tiger populations and the need for a more focused, accountable, and legally empowered body to oversee their protection
- NTCA has the power to issue binding directions to states regarding tiger conservation. It also coordinates with law enforcement agencies, forest departments, and international organizations to curb wildlife crime and illegal trade in tiger parts
- The NTCA plays a central role in India's tiger conservation success, helping the country maintain over 70% of the world’s wild tiger population. Through data-driven conservation, policy advocacy, and strict protection measures, NTCA has helped reverse the decline in tiger numbers, as reflected in the results of All India Tiger Estimations
Key Features of Project Tiger:
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Tiger Reserves:
Specially designated protected areas known as tiger reserves were established. India began with 9 reserves in 1973; as of now (2024), there are over 53 tiger reserves across 18 states. -
Core-Buffer Strategy:
Each tiger reserve is divided into:-
Core Zone: Strictly protected; human activity is prohibited.
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Buffer Zone: Sustainable use area where conservation and local livelihoods coexist.
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Monitoring & Research:
Uses scientific methods like camera traps, pugmark tracking, and radio telemetry. The All India Tiger Estimation is conducted every four years. -
Community Participation:
Local communities are involved through eco-development programs to reduce dependence on forest resources and promote conservation awareness. -
Rehabilitation and Relocation:
Voluntary relocation of villages from core areas to reduce pressure on tiger habitats
🐅 Tiger’s Conservation Status – Know the Protection Levels!
🔖 Under the Wildlife Protection Act, 1972 🌍 IUCN Red List Classification 🌐 CITES (Convention on International Trade in Endangered Species) |
For Prelims: Kaziranga National Park, Indian Forests Act, 1927, Wildlife Protection Act, 1972
For Mains:
1. What are the prohibitions for visitors in case of National Parks, Discuss the laws governing National Parks and Tiger reserves
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