UPSC Prelims 2026 Revision Checklist: Top 30 Geography topics aspirants shouldn’t miss

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Other Revision Checklists: Top 30 Environment topics | Top 20 Reports and Indices | Top 25 places in News

#1. Western Disturbances

— Western Disturbances are east-moving rain-bearing wind systems that originate beyond Afghanistan and Iran, and pick up moisture from the Mediterranean Sea, Black Sea, Caspian Sea and the Arabian Sea. These are typically extra-tropical cyclones resulting from low-pressure areas, formed by interactions between polar and tropical winds.

— Western Disturbances are embedded within the subtropical westerly jet stream, which is a high-altitude, fast-moving air current that flows from west to east in the Earth’s atmosphere. It is found over the Himalayan and Tibetan highlands.

#2. Acid rain

— Acid rain depletes the soil of essential nutrients such as calcium and magnesium, weakening tree roots, damaging leaves, and eliminating species diversity in forests. Lakes and rivers become lifeless. For instance, when the oil wells of Kuwait were burning in 1991, thousands of hectares of land became completely barren.

— The acid rain caused by toxic smoke, which contains very high levels of sulphur dioxide, nitrogen oxides, hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), and PM2.5, small particles of 2.5 microns or less in diameter, which, when combined with water vapour in the atmosphere, produce sulphuric acid and nitric acid with a pH level less than 5.6.

#3. Sijimali

— Sijimali is part of the Eastern Ghats hill ranges and is interspersed with valleys. The bauxite reserve, covering an area of 1,500 hectares, is spread over the Rayagada and Kalahandi districts. With an estimated reserve of 311 million tonnes of high-grade bauxite, Sijimali is located close to Vedanta’s alumina refinery at Lanjigarh in Kalahandi district, capable of producing 5 million tonnes per annum.

— Alumina is refined from bauxite ore and used to produce aluminium, which is instrumental in making everything from soda cans to aircraft. Aluminium’s strength, lightness and conductivity allow for a multiplicity of uses. It is also the most abundant metal in the Earth’s crust, and the third most common element, after Oxygen and Silicon.

— According to the Indian Bureau of Mines’ 2022 Yearbook, Odisha alone accounts for 41% of India’s bauxite resources, and was the leading producer in 2021-22, comprising about 73% of the total production. Beyond bauxite, Odisha has some of the richest mineral deposits in the country, including high-grade iron ore, coal, nickel, gemstones and graphite, together accounting for nearly 17% of India’s total mineral reserves.

#4. Nor’wester

— These are localised rainfall and thunderstorm events which occurs in the region of Eastern South Asia.

— According to some authors, nor’westers are single air mass thunderstorms while according to others nor’wester thunderstorms are associated with cold fronts moving with the passage of extra-tropical disturbances.

#5. Hormuz mountains

— These mountain ranges, which have deposits of salts and minerals, forged through the collision of tectonic plates. The process of their formation began roughly 500-600 million years ago, during the Late Precambrian to Early Cambrian period. Over time, these salt beds were buried under innumerable layers of marine sediment and volcanic rock.

#6. Bab el-Mandeb strait

— The Bab el Mandeb is a 20-mile-wide, 70-mile-long strait between the Horn of Africa and the southern tip of the Arabian Peninsula, serving as the southern entry to the Red Sea from the Gulf of Aden and the Indian Ocean beyond.

Source: US Energy Energy Information Administration

— It is bordered to the west by Eritrea and Djibouti, and to the east by Yemen.

#7. Dzukou Valley

— Dzukou Valley, on the border of Nagaland and Manipur, offers a high-altitude plateau that turns stark and dry in certain months, resembling a meadow-desert hybrid.

#8. Indira Point

— The National Green Tribunal (NGT) cleared the way for the government’s Rs 81,000-crore Great Nicobar mega infrastructure project, noting its “strategic importance” and observing that there were “adequate safeguards” in the project’s environmental clearance.

— Great Nicobar Island covers 910 sq km and is home to India’s southernmost location, Indira Point.

#9. Mountain Railway of India

— Northern Railway (NR) rolled out the first rake of Narrow Gauge (NG) coaches equipped with an indigenously-developed air brake system on the prestigious Kalka-Shimla UNESCO World Heritage rail line.

— The Mountain Railway of India consists of three railways: the Darjeeling Himalayan Railway located in the foothills of the Himalayas in West Bengal (Northeast India) having an area of 5.34 ha., the Nilgiri Mountain Railways located in the Nilgiri Hills of Tamil Nadu (South India) having an area of 4.59 ha. and the Kalka Shimla Railway located in the Himalayan foothills of Himachal Pradesh (Northwest India) having an area of 79.06 ha.

#10. National Large Solar Telescope

— The government sanctioned the establishment of two new telescopes to study the sun and the origins of the universe, besides the upgradation of an existing telescope, in Ladakh.

— Ladakh is already a major centre of astronomy in the country, being home to several big and small telescopes. There, the village of Hanle also has been identified as India’s first and only Dark Sky Reserve, a protected area meant to preserve the natural darkness of the night sky. Due to the high altitude, cold and dry atmospheric conditions, and mostly clear skies in Ladakh, data from NLOT will not suffer diffraction, which is common in other locations.

#11. Silk Route

— The Indian stretch of the legendary Silk Route once connected Ladakh and Himachal Pradesh to Tibet, China, and Central Asia. Traders moved silk, wool, spices, horses, and turquoise across high-altitude passes such as Zoji La and Baralacha La.

— The Indian stretch of the legendary Silk Route once connected Ladakh and Himachal Pradesh to Tibet, China, and Central Asia. Traders moved silk, wool, spices, horses, and turquoise across high-altitude passes such as Zoji La and Baralacha La.

#12. Polar vortex

— The polar vortex is a large area of low-pressure and cold air that swirls like a wheel around both of the Earth’s polar regions. There are two types of polar vortex: tropospheric and stratospheric.

— The tropospheric polar vortex occurs at the lowest layer of the atmosphere — it extends from the surface up to about 10 km to 15 km — where most weather phenomena occur.

Source: NOAA

— The stratospheric polar vortex occurs at around 15 km to 50 km high. Unlike the tropospheric polar vortex, the stratospheric polar vortex disappears during the summer and is the strongest during the autumn. The tropospheric polar vortex is associated with the Polar jet stream while the stratospheric polar vortex is associated with the Polar night jet

#13. Mt Aconcagua

— Standing at 22,841 feet in Argentina’s Andes range, Mt. Aconcagua is the highest peak in South America and the tallest mountain outside of Asia. Though lower than Everest, Mt Aconcagua has a success rate of only about 30 per cent. During winter, temperatures plunge below zero degrees, wind speed reaches above 100 kmph, and high altitude presents constant challenges.

— Aconcagua is one of the Seven Summits, or the highest points on each of the seven continents. The first known attempt to climb the mountain’s summit was in 1883, but it failed. In 1897, Swiss mountaineer Matthias Zurbriggen became the first known climber to reach the summit.

#14. Shaksgam Valley

— Shaksgam Valley, or the Trans Karakoram Tract, is part of the Hunza-Gilgit region occupied by Pakistan and lies to the north of the Siachen glacier. Spread over more than 5,000 sq km, its terrain and climatic conditions make it difficult for human habitation. While it is claimed by India, Pakistan used to control it.

— It borders China’s Xinjiang province to the north and the Gilgit-Baltistan region (Pakistan-occupied Kashmir) to the west.

#15. Bomb cyclone

— A powerful “bomb cyclone” barreled across the northern United States, triggering severe winter weather in the Midwest and the East Coast.

— Storms typically form when a mass of low-pressure air meets a high-pressure mass. The air flows from high pressure to low, creating winds. A bomb cyclone forms due to the interaction between contrasting warm and cold air masses.

— What defines a bomb cyclone is how rapidly the pressure drops in the low-pressure mass, by at least 24 millibars in 24 hours. This quickly increases the pressure difference, or gradient, between the two air masses, therefore making the winds stronger. This process of rapid intensification has an even more ferocious-sounding name: bombogenesis.

#16. Aravalli Ranges

— At over a billion years old, the Aravallis are one of the oldest mountain ranges in the world, formed during the Precambrian Era due to the collision of tectonic plates of the earth’s crust. The 700-odd-km range stretches across four states (Gujarat, Rajasthan, Haryana and Delhi) and 37 districts, with 560 km lying in Rajasthan.

— The highest peak of the Aravalli mountain range is Guru Shikhar, located in the Sirohi district of Rajasthan. The range also supports water recharge systems and is the source of important rivers such as Chambal, Sabarmati, and Luni. Its forests, grasslands, and wetlands harbour endangered flora and fauna, contributing to biodiversity and regulating precipitation through evapotranspiration, which helps mitigate droughts.

— The Aravallis provide priceless ecological services. If the Western Ghats are considered the water tower and climate regulator of peninsular India, the Aravalli range is an ecological shield for the plains of Northwest and North India.

#17. Shyok Tunnel

— Shyok Tunnel is a 920-metre cut-and-cover tunnel on the 255 km long DS-DBO road, which is the only operational road connecting Durbuk to the Depsang Plains and DBO in the north. DBO hosts one of the world’s highest operational airfields, which is a key strategic air infrastructure for India.

— Shyok tunnel is strategically significant in its ability to provide round-the-year connectivity to areas close to the LAC. It would particularly help in the quick mobilisation and redeployment of troops in case of any emergency.

#18. Sambhar Lake

— Flamingos visit Sambhar Salt Lake as part of their annual migration along the Central Asian Flyway. They travel from regions in Africa, the Middle East, and Central Asia, arriving between October and March to breed and feed in the lake’s saline waters. The lake’s shallow waters and abundant food make it an ideal stopover during their long migratory journey.

— The Sambhar Salt Lake, located in Sambhar Lake Town in Jaipur district of Rajasthan, is India’s largest inland salt lake.

#19. Northeast Monsoon

— As the southwest monsoon begins to fade, the northeast monsoon sets in by October. This is also called the retreating monsoon. It is shorter and less widespread but still important, especially for southern India.

— As the southwest monsoon begins to fade, the northeast monsoon sets in by October. This is also called the retreating monsoon. It is shorter and less widespread but still important, especially for southern India.

— Because these winds travel over the Bay of Bengal before reaching the southeastern shore, they take up moisture. As they travel across Tamil Nadu, south Andhra Pradesh, and parts of Sri Lanka, they supply ample moisture for rainfall activity. This rain is crucial for areas such as Tamil Nadu, which do not receive much during the southwest monsoon. Weather systems originating over the south Bay of Bengal bring ample rainfall to the south Peninsula. The southwest monsoon is especially important for crops like rice, cotton, and sugarcane.

#20. Hygroscopic clouds

— Hygroscopic clouds are rare and form under specific atmospheric conditions. They typically appear during the pre-monsoon period and throughout the monsoon. Hygroscopic clouds arise at lower altitudes as moisture-laden air cools around hygroscopic particles, rather than by freezing.

— Cloud seeding only works with hygroscopic or warm-rain clouds, because they have abundant water content and respond quickly when extra nuclei are introduced.

#21. Tropical Cyclone and ‘landfall’ of a cyclone

— Tropical cyclones form over warm ocean waters near the equator. When the warm, moist air from the ocean surface rises upward, a lower air pressure area is formed below. Air from surrounding areas with higher air pressure rushes into this low-pressure area, eventually rising, and it becomes warm and moist. As warm, moist air rises, it cools down, and the water in the air forms clouds and thunderstorms. This whole system of clouds and winds gains strength and momentum using the ocean’s heat, and the water that evaporates from its surface.

— Tropical cyclones are characterised by destructive winds, torrential rainfall and storm surges disrupt normal life with the accompanying phenomena of floods due to the exceptional level of rainfall and storm surge inundation into inland areas.

— Tropical cyclones rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere due to the Coriolis effect.

— Landfall is the event of a tropical cyclone coming onto land after being over water. As per the India Meteorological Department (IMD), a tropical cyclone is said to have made landfall when the centre of the storm – or its eye – moves over the coast.

— Crucially, a landfall should not be confused with a ‘direct hit’, which refers to a situation where the core of high winds (or eyewall) comes ashore but the centre of the storm may remain offshore. As per the US National Oceanic and Atmospheric Administration (NOAA), because the strongest winds in a tropical cyclone are not located precisely at the centre, it is possible for a cyclone’s strongest winds to be experienced over land even if landfall does not occur.

#22. Western Ghats

— The Western Ghats are internationally recognized as a region of immense global importance for the conservation of biological diversity, besides containing areas of high geological, cultural and aesthetic values. A chain of mountains running parallel to India’s western coast, approximately 30-50 km inland, the Ghats traverse the States of Kerala, Tamil Nadu, Karnataka, Goa, Maharashtra and Gujarat.

— The mountains of the Western Ghats and their characteristic montane forest ecosystems influence the Indian monsoon weather patterns that mediate the warm tropical climate of the region, presenting one of the best examples of the tropical monsoon system on the planet. The Ghats act as a key barrier, intercepting the rain-laden monsoon winds that sweep in from the south-west during late summer.

#23. Glacial Lakes and Water Bodies

— In the monthly monitoring report of Glacial Lakes and Water Bodies for June 2025 which was recently made public, the CWC said 432 glacial lakes spread across Ladakh, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, Sikkim and Arunachal Pradesh have been flagged for vigorous monitoring because of their potential to unleash sudden and destructive floods.

— Arunachal Pradesh accounts for the highest number of expanding lakes (197), followed by Ladakh (120), Jammu and Kashmir (57), Sikkim (47), Himachal Pradesh (6) and Uttarakhand (5). Overall, the Himalayan region saw 1,435 glacial lakes expand in June 2025.

#24. Ring of Fire

— The Ring of Fire is essentially a series of hundreds of volcanoes and earthquake sites that span along the Pacific Ocean.

— The Pacific ‘Ring of Fire’ or Pacific rim, or the Circum-Pacific Belt, is an area along the Pacific Ocean that is characterised by active volcanoes and frequent earthquakes. It is home to about 75 per cent of the world’s volcanoes – more than 450 volcanoes. Also, about 90 per cent of the world’s earthquakes occur here.

(Source: W. Jacquelyne and Robert I. Tilling via USGS)

— Its length is over 40,000 kilometres and traces from New Zealand clockwise in an almost circular arc covering Tonga, Kermadec Islands, Indonesia, moving up to the Philippines, Japan, and stretching eastward to the Aleutian Islands, then southward along the western coast of North America and South America. The area is along several tectonic plates including the Pacific plate, Philippine Plate, Juan de Fuca plate, Cocos plate, Nazca plate, and North American plate. The movement of these plates or tectonic activity makes the area witness abundant earthquakes and tsunamis every year.

#25. Santa Ana winds

— Santa Ana winds blow when high pressure builds over the Great Basin — the area between the Rocky Mountains and Sierra Nevada — and pressure is low over California’s coast. The difference in pressure triggers powerful winds that move from the Basin’s inland deserts east and north of Southern California towards the Pacific Ocean.

— As the wind comes down the mountains, it compresses and heats up, and its humidity falls — sometimes to less than 10%. The hot, dry wind dries out forests, and fuels wildfires. Santa Ana winds are a natural part of California’s climate pattern, and usually blow from October to January.

#26. Wular lake

— Wular Lake, located about 67 kilometres from Srinagar and surrounded by the foggy Harmukh mountains, is once again becoming home to lotuses, 30 years after a disastrous flood swept them out of the area. It is the largest freshwater lake in India.

— The Jhelum River feeds the lake basin, which formed as a result of tectonic activity. The lake is one of the Indian wetlands which is classified as Ramsar sites. However, it suffers environmental challenges such as the conversion of major portions of the lake’s catchment areas to agricultural land, pollution from fertilisers and animal waste, hunting of waterfowl and migrating birds, and weed infestation in the lake itself.

— The Tulbul Project is a “navigation lock-cum-control structure” near the outlet of Wular Lake.

#27. Vanishing stars

— Astronomers have now observed “vanishing stars”, massive stars that simply fade from view without a bright explosion. In these cases, the star appears to collapse directly into a black hole, swallowing itself so completely that little light escapes. These failed supernovae confirm a long-standing prediction: some stars die quietly, forming black holes almost invisibly. It is gravity acting without drama – and without mercy.

Note: Aspirants must also read about other celestial bodies in news.

#28. River Basin in News

(i) Banas River

— The Banas River Basin is located in eastern Rajasthan and covers a substantial area to the east of the Aravali mountain range. It is bordered in the east by the Chambal river basin, in the north by the Gambhir and Banganga river basins, in the west by the Shekhawati and Luni river basins, and in the south by the Sabarmati and Mahi river basins. It feeds into the Chambal River, which then flows into the Yamuna.

— The Banas River originates in the Khamnor Hills of the Aravali Range, approximately 5 km from Kumbhalgarh in Rajsamand District, and runs entirely through Rajasthan. It flows northeast through Rajasthan’s Mewar area, eventually meeting the Chambal River near the village of Rameshwar in Khandar Block, Sawai Madhopur District.

(ii) Subansiri River basin

— The Subansiri basin spans sections of Tibet (China), Arunachal Pradesh, and Assam in India, beginning in Tibet and flowing through Arunachal Pradesh before entering Assam’s plains and joining the Brahmaputra.

(iii) Teesta basin

— Teesta basin in West Bengal forms its boundary with Sikkim state in the North through the RamamKhola, Rangit and Teesta rivers. It shares its border with Nepal and Mahananda river basin in West, Jaldhaka river basin in East and Bangladesh in the south.

— Teesta sub-basin in West Bengal covers an area of 3225 sq. Km. which comprises hilly terrain of Darjeeling district (approximately 1121 sq. km) and plains of Jalpaiguri district (2104 sq. km).

(iv) Barak Valley

— The Barak sub-basin drains portions of India, Bangladesh, and Myanmar. The drainage area of the site in India is 41723 square kilometres, accounting for about 1.38% of the country’s total geographical area. The sub-basin lies in the States of Meghalaya. Manipur, Mizoram, Assam, Tripura and Nagaland.

(v) Mahanadi River basin

— The Mahanadi basin has a maximum length of 587 km and breadth of 400 km. It is bounded by the Central India hills to the north, the Eastern Ghats to the south and east, and the Maikala range to the west.

— The Mahanadi basin covers the states of Chhattisgarh and Odisha, as well as lesser areas of Jharkhand, Maharashtra, and Madhya Pradesh, and drains an area of 1,41,589 Sq.km, or roughly 4.3% of the country’s entire geographical area. The Mahanadi is a large river in the country, and among peninsular rivers, it ranks second only to the Godavari in terms of water potential and flood producing capacity.

#29. Tiger Reserves/National Park/Wildlife Sanctuaries/Mangroves in News

(i) Bandhavgarh Tiger Reserve

— The Bandhavgarh Tiger Reserve is located between the Vindhyan and Satpura ranges of Madhya Pradesh. The habitat is characterized by valleys, hills and plains, with the Bandhavgarh fort prominently seen as a major landmark.

(ii) Veerangana Durgavati Tiger Reserve

— The Veerangana Durgavati Tiger Reserve is along the Byarma River and the Kopra River. Notified in 2023 and spread over 2,339.12 sq km, the Durgavati tiger reserve was carved out of the Nauradehi wildlife sanctuary, and is home to tigers, leopards, hyena, sambar, sloth bear, among other species.

(iii) Kuno National Park

— At Madhya Pradesh’s Kuno National Park, India-born cheetah Mukhi has given birth to five cubs. Mukhi is the sole surviving cheetah cub born in India at Kuno, a landmark for the country’s cheetah reintroduction project.

— At present, India has 34 cheetahs, including 10 adults and 24 cubs. The big cat had been extinct in the wild in India before 20 individuals were transported from southern Africa in two batches in 2022 and 2023.

(iv) Similipal Tiger Reserve

— Similipal Tiger Reserve, located in Mayurbhanj, Northern Odisha, is a location where Nature captivates you with its breathtaking beauty, grace, power, and tranquillity. The Similipal Tiger Reserve, which covers an area of 2750 square kilometres, is Odisha’s premier wildlife sanctuary. Similipal is named from red silk cotton semul trees, which are widespread in the area. The striking black tiger has been sighted in Similipal Tiger Reserve.

(v) Kaziranga Tiger Reserve

— The Kaziranga Tiger Reserve has the world’s third-highest tiger density, according to the first large-scale survey of the big cat population. Officials estimate that the reserve has 18.65 tigers per 100 square km. It is home to the world’s largest population of one-horned rhinoceros.

— The variations of the Brahmaputra River create stunning examples of riverine and fluvial processes in this huge area of wet alluvial tall grassland, intermingled with several broad shallow lakes bordered with reeds and patches of deciduous to semi-evergreen woods. Kaziranga National Park was included to the World Heritage List in 1985 because of its enormous population of one-horned rhinos, tigers, elephants, panthers, bears, and many birds, as well as its portrayal of the Brahmaputra floodplain and grassland ecology that has not been altered by humans.

— The first grassland bird census was conducted at Assam’s Kaziranga National Park. Kaziranga National Park is one of the last unaltered natural places in India’s northeast.

(vi) Sundarbans mangrove forest

— The Sundarbans Reserve Forest (SRF), located in the south-west of Bangladesh between the rivers Baleswar and Harinbanga, and bordering the Bay of Bengal, is the world’s biggest contiguous mangrove forest.

— The Sundarbans mangrove forest, one of the world’s largest (140,000 acres), is located on the delta of the Ganges, Brahmaputra, and Meghna rivers in the Bay of Bengal. It is near India’s Sundarbans World Heritage Site, which was designated in 1987. The area is recognised for its diverse wildlife, which includes 260 bird species, the Bengal tiger, and other threatened species like the estuarine crocodile and Indian python.

#30. Clarion-Clipperton Zone

—  The Clarion-Clipperton Zone (CCZ) is an abyssal plain in the Pacific Ocean. Recently, a discovery was made in this region when marine biologist Dr Alejandra Mejía-Saenz’s remotely operated vehicle (ROV) was scanning the ocean depths for a mining impact survey. In the clipping, a slender, whip-tailed squid was seen approaching a muddy patch dotted with polymetallic nodules.

— The species was seen approaching a muddy patch dotted with polymetallic nodules. The animal then plunged headfirst into the sediment, burying its mantle deep into the patch. As it took this weird dive, only its long tentacles and hyponome, a tubular organ, were seen swaying in the water currents, resembling rigid sponge stalks. As the squid positioned itself in this upside-down pose, it froze, masquerading as deep-sea flora amid the barren plain.

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