The Himalayan mountain system is about 160 to 320 km (about 100 to 200 mi) wide and extends about 2,400 km (about 1,500 mi) along the northern and eastern borders of India. It includes the mountains surrounding the Vale of Kashmîr the Karakoram Range, and the central and eastern Himalayas. Ancient geological forces molded the Himalayas as the Indian plate of the earth’s crust burrowed under the Eurasian landmass, creating an uplift that continues to push this northernmost boundary of India ever higher. The Himalayan Range is the highest mountain system in the world. Among its towering summits, wholly or partly within India or within territory claimed by India and administered by Pakistan, are K2 (8,611 m/28,251 ft) and Kânchenjunga (8,598 m/28,209 ft), which are the second and third highest peaks in the world after Mount Everest. Other prominent Indian peaks include Nanga Parbat (8,125 m/26,657 ft), Nanda Devi (7,817 m/25,645 ft), Rakaposhi (7,788 m/25,551 ft), and Kâmet peak (7,756 m/25,446 ft). The Himalayas region, including the foothills, is sparsely settled. Agriculture and animal herding are the main economic activities.

South and parallel to the Himalayas lies the Gangetic Plain, a belt of flat, alluvial lowlands about 280 to 400 km (about 175 to 250 mi) wide. This area includes some of the most agriculturally productive land in India. The Indian portion of the broad Gangetic Plain encompasses several river systems, and stretches from Punjab State in the west, through the Gangetic Plain, to the Assam Valley in the east. Marking the western end of the Gangetic Plain are the Indus River and its tributaries, including the Sutlej and Chenâb rivers, which flow through Punjab in India’s northwest corner. The Gangetic Plain is formed by the Ganges River and its tributaries, which drain the southern slopes of the Himalayas. Assam Valley is separated from the Gangetic Plain by a narrow corridor of land near the city of Dârjiling (Darjeeling). Assam is watered by the Brahmaputra River, which rises in Tibet and crosses into India at its northeast corner, then flows north of the Khâsi Hills into Bangladesh. The Thar Desert, a huge dry, sandy region extending into Pakistan, lies at the southwestern end of the Gangetic Plain.

In the southern part of peninsular India lies the vast Deccan Plateau, a tableland lying within a triangle formed by the Sâtpura Range, the steep mountain slopes of the Western Ghats, and the gentler slopes of the Eastern Ghats. Elevations in the plateau region average about 600 m (about 2,000 ft), although outcroppings as high as about 1,200 m (4,000 ft) occur. At their northern end, the Western Ghats vary in height from about 900 to 1,200 m (about 3,000 to 4,000 ft), but the Nîlgiri Hills of the extreme south reach a height of 2,637 m (8,652 ft) at Doda Betta, their highest peak. The Eastern Ghats lie along the eastern flank of the Deccan Plateau, interrupted by the Krishna and Godâvari river basins. Elevations of the Eastern Ghats are much lower, averaging about 600 m (about 2,000 ft). The plateau itself, even rockier than the northern extension of peninsular India, supports a sparse agricultural population and is also home to industrial enterprises.

The Indian Peninsula is bordered by a mostly fertile seashore. The west coast, including the extensive Gujarât Plain in the north, the thin Konkan shore in Mahârâshtra State, and the Malabar Coast in the south, support substantial populations of farmers and fishermen. Ancient trade routes to the west helped make the cities and towns of this region into market centers for textiles and spices. The east coast’s broad alluvial plains, stretching from the Kâveri River delta in the south to the Mahânadî River delta in the north, are intensely farmed.

The Indian subcontinent’s three great northern rivers, the Indus, the Brahmaputra, and the Ganges, flow through India. The Indus (about 2,900 km/1,800 mi long) originates in the Himalayas of western Tibet, flows through the Ladakh region of Jammu and Kashmîr State, then enters Pakistan. The waters of three of its tributaries, the Sutlej, Râvi, and Chenâb have been diverted, under the Indus Water Treaty, for use in India. The Brahmaputra (about 2,900 km/ 1,800 mi long) likewise rises in the Tibetan Himalayas. It flows through Assam state and then south through Bangladesh to the Bay of Bengal. The Ganges (about 2,510 km/ 1,560 mi long), known as Ganga in India, rises in the Indian Himalayas and enters the Gangetic Plain north of Delhi. At Allahâbâd it is joined by its major tributary, the Yamuna. The main branch of the Ganges flows through Bangladesh to the Bay of Bengal, while a second branch meets the bay in India, near Calcutta. Both the Brahmaputra and Ganges rivers discharge enormous amounts of water, almost all of it during the monsoon season.

The Narmada (1,289 km/801 mi long) is India’s major west-flowing river; it flows mainly in the state of Madhya Pradesh, emptying into the Arabian Sea in Gujarât state. Its annual runoff is less than one-tenth that of the Ganges system. Its basin consists of about 5 million cultivable hectares (about 12 million acres), though only a small percentage is currently irrigated. A major dam system under construction will divert large amounts of water for irrigation, particularly in the state of Gujarât.

Three major rivers flow east into the Bay of Bengal, rising from the western hills of the Deccan Plateau. The northernmost is the Godâvari (about 1,400 km/900 mi long). It has a basin (the area drained by a river) one-third the size of the Ganges, and carries one-tenth of the amount of water the Ganges carries. Emptying into the sea not far south of the Godâvari is the Krishna (about 1,300 km/800 mi long), with a basin equal to the Godâvari but carrying only two-thirds of the amount of water. The smallest of the three rivers is the Kâveri (760 km/470 mi long), with a basin less than one-third the size of the other two rivers.

India has a number of other significant rivers. Tributaries of the Ganges from the north include the Kosi, Gandak, Ghâghara, Gumti, and Sârda rivers. Joining the Ganges from the south are the Betwa, Chambal, and Son rivers. The Mahi, Sâbarmatî, and Tâpi flow west into the Arabian Sea in Gujarât. Flowing west to join the Indus River in Pakistan are the Beâs, Chenâb, Jhelum, Râvi, and Sutlej, all rivers of the Punjab (Hindi for "five rivers") region of India and Pakistan. The Mahânadî and Brâhmani rivers rise in Madhya Pradesh and Orissa states, respectively, and flow east to empty into the Bay of Bengal. The waters of all these rivers are used to irrigate crops, but the amount stored for purposes of irrigation and power generation varies enormously from river to river depending, among other things, on the number of dams on the river.

There are only a few natural lakes in India of any size. Chilika Lake on the coast of Orissa varies seasonally in volume and is alternately fresh and salty. Other lakes, such as Sâmbhar in Râjasthân state and Colair in Orissa state, typically dry out completely before the monsoon begins. Small artificially created ponds called tanks are a feature of virtually every village, serving as sources of water for drinking, bathing, and irrigation.

India has an estimated 45,000 species of plants, 33 percent of which are native. There are 15,000 flowering plant species, 6 percent of the world's total. About 3,000 to 4,000 of the total number of plant species are believed to be threatened with extinction.

In the arid areas that adjoin Pakistan, the eastern part of the Indus Plain, most plant life is sparse and herblike. Various thorny species, including capers (spiny shrubs with pale flowers) and jujubes (fruit-producing trees with veined leaves and yellowish flowers), are common. Bamboo grows in some areas, and among the few varieties of trees is the palm. The Gangetic Plain, which has more moisture, supports many types of plant life. Vegetation is especially luxuriant in the southeastern part of the plains region, where the mangrove and the sal, a hardwood timber tree, flourish.

In the Himalayas many varieties of arctic flora are found on the higher slopes. The lower levels of the mountain range support many types of subtropical plant life, notably the orchid. Dense forests remain in the few areas where agriculture and commercial forestry have had little effect. Coniferous trees, including cedar and pine, predominate in the northwestern Himalayan region. On the Himalayas’ eastern slopes, tropical and subtropical types of vegetation abound. Here rhododendrons grow to tree height. Among the predominant trees are oak and magnolia.

The Assam Valley features evergreen forests, bamboo, and areas of tall grasses. The Malabar Coast, which receives a large amount of rainfall, is thickly wooded. Evergreens, bamboo, and several varieties of valuable timber trees, including teak, predominate in this region. Extensive tracts of impenetrable jungle are found in the swampy lowlands and along the lower elevations of the Western Ghats. The vegetation of the peninsular plateau is less luxuriant, but thickets of bamboo, palm, and deciduous trees grow throughout the Deccan Plateau. The Andaman and Nicobar Islands have tropical forests, both evergreen and semievergreen.

India is inhabited by a wide variety of animal life, including almost 5,000 species of larger animals. Several species of the cat family—including the tiger, panther, Asiatic lion, Asiatic cheetah, snow leopard, jungle cat, and clouded leopard—live in some areas of India. Most of these species are under threat of extinction. Elephants roam the lower slopes of the central and eastern Himalayan foothills and the remote forests of the southern Deccan Plateau. Other large quadrupeds (four-footed animals) native to India include rhinoceroses (under threat of extinction), black bear, wolf, jackal, dhole (wild Asian dog), wild buffalo, wild hog, antelope, and deer. Several species of monkeys live throughout the country.

Various species of wild goats and sheep, including ibexes and serows, are found in the Himalayas and other mountainous areas. The pygmy hog, bandicoot rat, and tree mouse are typical types of smaller native quadrupeds; bats are also abundant. Venomous reptiles, including the cobra, krait, and saltwater snake, are especially numerous in India, and pythons and crocodiles are also found. Tropical birds of India include the parrot, peacock, kingfisher, and heron. The rivers and coastal waters of India teem with fish, including many edible varieties.

The black and red soils of the Deccan Plateau, though not as thick as the Gangetic Plain alluvium, are also fertile. The groundwater resources of the Deccan are significant but more difficult to reach, so most farmers rely on the monsoons for water. Farmers typically grow a single crop, including coarse grains such as sorghum, maize (corn), or millet, and cotton.

Forests constitute another natural resource for India, with woodlands covering 21.9 percent of its land area. India's highly varied climate and land produce diverse forests. The majority are deciduous, both tropical-dry, experiencing a significant dry season, and tropical-moist, receiving relatively uniform rainfall year-round. The remainder of forests range in type from tropical evergreen to Himalayan temperate and alpine. Major commercial tree species include teak, rosewood, and sal. Bamboo is a widely used construction material. Despite significant overuse of forest resources in the past, government and private efforts have reduced the rate of deforestation in natural forests, and increased new plantations of trees, creating a modest net gain in forest cover since 1990.

The mineral resources of India include a vast belt of coal stretching from eastern Mahârâshtra state through the hill areas of Madhya Pradesh and Bihâr to West Bengal. The same geographical area, with the addition of Orissa state, contains major deposits of bauxite. Iron ore is also found here, as well as in the Western Ghats in and around Goa. Other mineral deposits include manganese (found mainly in central India), copper, and chromite. There are significant oil and natural gas reserves in Assam and Gujarât states, and on the continental shelf off Mahârâshtra and Gujarât. India also has ample reserves of phosphate rock apatite, gypsum, limestone, and mica.

India’s seasonal cycle includes three main phases: the cool, dry winter from October to March; the hot, dry summer from April to June; and the southwest monsoon season of warm, torrential rains from mid-June to September. India’s winter season brings cold temperatures to the mountain slopes and northern plains; temperatures in the Thar Desert reach freezing at night. Farther south, temperatures are mild. Average daily temperatures in January range from 13° to 27° C (55° to 81° F) in the northeastern city of Calcutta; from 7° to 21° C (44° to 70° F) in the north central city of Delhi; from 19° to 28° C (67° to 83° F) in the west central coast city of Mumbai (formerly Bombay); and from 19° to 29° C (67° to 85° F) in the vicinity of Chennai (formerly Madras) on the southeastern coast. Dry weather generally accompanies the cool winter season, although severe storms sometimes traverse the country, yielding slight precipitation on the northern plains and heavy snowfall in the Himalayas.

India’s hot and dry season reaches its most oppressive stage during May, when temperatures as high as 49° C (120° F) are commonly recorded in the northern plains. Temperatures in the southern peninsula are somewhat lower, averaging 35° to 40° C (95° to 104° F). At higher altitudes, as in the Western Ghats and the Himalayas, temperatures are considerably cooler.

The intense heat breaks when the summer monsoon season arrives in June. For most of the year the monsoons, or seasonal winds, blow from the northeast. In the summer months, however, they begin to blow from the southwest, absorbing moisture as they cross the Indian Ocean. This warm, moist air creates heavy rains as it rises over the Indian Peninsula and is finally forced up the slopes of the Himalayas. The rains start in early June on a strip of coast lying between the Arabian Sea and the foot of the Western Ghats. A second "arm" of the monsoon starts from the Bay of Bengal in the northeast and gradually extends up the Gangetic Plain, where it meets the Arabian Sea "arm" in the Delhi region around July 1. In July the average daily temperature range is 26° to 32° C (79° to 89° F) in Calcutta; 27° to 36° C (81° to 96° F) in Delhi; 25° to 29° C (77° to 85° F) in Mumbai; and 26° to 36° C (79° to 96° F) in Chennai.

The monsoon season is critical to India. Farming depends heavily on the monsoon, even though artificial sources of irrigation are also commonly used. The economy prospers when the monsoon season is normal and plummets when it is not. In the past a failure of the monsoon has brought abnormally low rains in crucial food-growing regions, leading to famine. A failed monsoon season in the dryland areas of the Deccan Plateau can mean poor or nonexistent harvests for that year’s crop. In the Gangetic Plain, the groundwater needed for irrigating the winter crop depends on the monsoon for replenishing. However, an excessive monsoon may also spell disaster, especially in the Gangetic Plain of eastern Uttar Pradesh and Bihâr, where rivers can flood and wash away homes and fields.

The average annual rainfall for India as a whole is 1,250 mm (about 49 in). The heaviest rainfall occurs along the Western Ghats, often more than 3,175 mm (more than 125 in), and on the slopes of the eastern Himalayas and the Khâsi Hills (of Meghalaya), where the town of Cherrapunji receives about 10,900 mm (about 430 in) annually. The entire northeast region averages more than 2,000 mm (about 80 in) annually, with the Bihâr plateau, Orissa, and the Bengal region receiving nearly as much. Rain and snow fall in abundance on the entire Himalayan range. New Delhi receives an annual average of about 800 to 1,000 mm (about 32 to 40 in) of rain, and the broad swath of land extending to the south, much of it in the rain shadow of the Western Ghats, receives about the same or a little more.

Expanding agrarian population has also affected wildlife. Farmers and herders have encroached on national park and other wildlife sanctuary land, and the spread of cultivation has limited the range of animals such as tigers and elephants outside of parks as well. Poaching is also a problem. To help combat these difficulties, the Indian government has enacted strong laws for forest conservation, wetland preservation, and wildlife protection, and established a Ministry of Environment and Forests in 1985.

India has a severe air pollution problem, generated by fumes from industry as well as from a burgeoning fleet of trucks, cars, and motor scooters. Water-treatment facilities have not kept pace with the increase in urban populations, and pollution of rivers and groundwater is a significant and worsening problem. Another major problem is toxic waste, generated by industry and deposited in rivers and oceans and on low-lying land within factory boundaries. Because of the large number of small industrial workshops, enforcement of laws against industrial waste pollution can be difficult.