A hydrographic organization centered on a few large basins corresponds to these morphological features. The largest is that of the Ganges (Ganga), between the Himalayas and the Central Highlands. The river, whose overall development is 2700 km, originates from the western Himalayas and flows into the plain north of Delhi, followed by its procession of Himalayan tributaries which, for a long stretch, given the vigor of their course, run parallel to the river greater before merging into it. The Yamuna, for example, reaches the Ganges in Allahabad after approx. 800 km from its outlet on the plain; more or less the same distance travels the Ghāghara before its confluence. Also the rivers that flow down from the Central Highlands (the Chambal and the Betwa tributaries of the Yamuna, the Son that pays directly to the Ganges) have oblique courses with respect to the major river that follows the depression axis of the gangetic fossa, much shifted towards the S due to the greater debris transport capacity of the left tributaries. At approx. 100 km from its mouth, the Ganges receives the contribution of the Brahmaputra, whose upper basin extends into the long longitudinal valley of Tibet and then, having crossed the Himalayas, occupies, in Indian territory, the section between the Himalayan side, Nagaland and the reliefs of Assam.
According to a2zcamerablog, the Brahmaputra basin is smaller than that of the Ganges (just over 600,000 km² out of a total of 1,125,000 km²), but its flow rate is greater (380,000 million m 3per year against 350,000 million in the Ganges), since it flows in very rainy areas. Both rivers have a nival regime in the upper section of their course; otherwise they are affected by monsoon rains and the variations in flow rate of the Ganges are particularly notable. An important element in the gangetic hydrography are the water tables, which emerge in the foothills of the Himalayas and can be reached with wells even in the most central part of the plain (in climatically more arid areas, such as in Bīhar). A portion of the Indus basin falls within the Indian territory (approx. 354,000 km² out of a total of 1,165,500 km²), extended from Punjab to the arid areas of Rājasthān. Among the rivers of Punjab only the Sutlej affects the country, and partially; for the rest, being arid lands, the hydrography in the whole section included in the Indus basin has a limited relief, with watercourses dry for most of the year, while more important, from the anthropic point of view, are the water tables that feed numerous oases of the Thar desert. As of this, the rivers that descend from the Arāvalli have an autonomous development: they have a seasonal regime and their contributions are responsible for the formation of the aforementioned rann, the brackish basins of Gujarāt. The Central Highlands feed numerous rivers. Some of them, as we have seen, pay tribute to the Ganges, others pour their waters into the two rivers which, in opposite directions, drain most of this region: the Narmada and the Mahānadi, the first flowing into the Arabian Sea (Gulf of Khambhāt), after having traveled the rift valley between the Vindhya and Sātpura mountains, the second in the Bay of Bengal. The Mahānadi has a rather extensive basin (132,100 km²) as it includes a section of the Deccan; it has a regime that is directly affected by monsoon precipitation and is therefore extremely irregular, giving rise to frequent flooding in the deltaic areas of Orissa. In the Deccan the largest hydrographic basins are those of the Godāvari (313,389 km²), Krishna (259,000 km²) and Kāveri (Cauvery, 72,500 km²); all three are born from the Western Ghats and head towards the Bay of Bengal, according to the characteristic morphology of the peninsula. In relation to this, the rivers of the Deccan which flow into the Arabian Sea have limited basins; the largest is the Tāpi, which drains the southern slope of the Sātpura mountains. The rivers of the Deccan also have an irregular regime connected with monsoon rainfall; however, the southern ones have a more regular regime given that the climate gradually becomes equatorial, proceeding towards the apex of the peninsula.
The vegetation cover of India is characterized by very different associations, which are however deeply tampered with by man today. Vegetal degradation affects the whole plain and a large part of the Deccan, where there are, however, strips of tropical forest in the southwestern slopes of the Deccan (slopes of the Western Ghats), in the mountain ridges of the Central Highlands, in the mountains of Assam and Nāgāland. It is an evergreen forest dominated by tall trees, which also include precious essences such as teak and sandalwood, although these trees are mainly typical of the peninsular region. Strips of evergreen forest are also found along the river courses of the interior, where however the deciduous tropical forest predominates, in which the dominant plant is the sal (Shorea robusta). Proceeding towards N and NW this forest assumes xerophilic adaptations: thus various species of acacias appear, which, rare and isolated, dominate the arid landscape of Rajasthan. The Himalayan slopes host subtropical forests, which gradually pass with increasing altitude into temperate forests (with oaks and conifers, among which the last characteristic is the Cedrus deodara), which are then followed by the typical high altitude alpine levels which also include rich pastures (mergs). § In India we can distinguish two faunal zones divided by the Ganges and by the reliefs of Vindhya and Satpura. Almost all the characteristic environments of the eastern zoogeographic region are represented in the N one: here live the nilgau, the cervicapra antelope, the caracal, a species of gazelle (Gazella gazella), the wild boar, as well as hedgehogs, shrews, bats and many rodents. In the central belt, the population of water birds is very numerous; near the mouth of the Indus the Asiatic lion still exists and many northern rivers are home to the Ganges dolphin (Platanista gangetica) and the gharial. The S area includes the real Indian peninsula whose typical animal is the tiger; in the mangrove formations it is not difficult to find the marsh crocodile and the marine crocodile as well as the banded monitor lizard and the Indian buffaloes. The sloth bear is also typical, still frequent in the dense woods of the Deccan; many monkeys, while the Lemuroids they are represented by the puny lori. Finally, the Asian elephant, the unicorn rhino, many cervids among which the muntjak (Muntiacus muntjak), many aquatic animals and many poisonous snakes that cause thousands of victims every year. The protected areas of the country cover 5% of the national territory, which is home to 94 national parks, 3 marine national parks and hundreds of nature reserves. Some of these areas have also been declared a World Heritage Site by UNESCO: these are the Manas Wildlife Sanctuary (1985), the Sundarbans National Park (1987), the Nanda Devi National Park (1988, 2005) and the Himalayan National Park (2014), which protects the western part of the range.