1. Himalayas protect the country against the cold arctic wind blowing from Siberia through Central Asia. This keeps the climate of northern India fairly warm throughout the year.
Since the cold is not so severe in the plains, people do not need heavy clothing and can live in the open for longer periods. Secondly the Himalayas are high enough to shield the country against invasions from the north.
2. Nested in the Himalayas are the valleys of Kashmir and Nepal. Surrounded on all sides by high mountains, the valley of Kashmir developed its own way of life. But it could be reached through several passes.
Its winter compelled some of its people to go to the plains and its summer attracted the shepherds of the plains. Economic and cultural interaction between the plains and the valley was continuous.
3. The Pamir plateau did not prevent it from becoming a transmitting centre of Buddhism for the adjacent areas of Central Asia. The valley of Nepal, smaller in size, is accessible to the people of the Gangetic plains through a number of passes.
4. The foothills of the Himalayas lent themselves of easier clearance than the jungles on the alluvial soil of the plains. It was easy to cross rivers in these areas because of their smaller width, and hence the earliest routes skirted along the foothills of the Himalayas from the west to the east and vice versa.
There are three great river systems, originating from the Himalayas which supply perennial water to this great plain. These are the Indus, the Ganga and the Brahmaputra. But a big tract of land to the west of Yamuna and east of Indus in the plain is devoid of any water system at present. This tract includes the states of Haryana, Punjab and Rajasthan.
The Sindhu or Indus rises from the Kailash Mansarovar area in the Tibetan plateau, runs west and north-west for about 1300 kms, between the Karakoram range. Then joined by the Gilgit river, it turns south and reaches the plains where the five rivers join it to form Punjab. These five tributaries of the Sindhu from east1 to west are-Sutlej, Beas, Ravi, Chenab and Jhelum.
The Ganga, rising from the Himalayas, reaches the plain at Haridwar and passes through the states of Uttaranchal, Uttar Pradesh, Bihar and Bengal, then joins the Bay of Bengal. On the west of it flows the river Yamuna also rising from the Himalayas. Some Vindhyan rivers like Chambal, Betwa and Kane join the Yamuna before its confluence with the Ganga at Allahabad. Another great Vindhyan river, Son, joins the Ganga near Patna in Bihar. From the Himalayas side, rivers like Gomati, Sarayu, Gandak and Kosi join Ganga in the states of Uttar Pradesh and Bihar. There are several mouth through which the Ganga falls into the Bay of Bengal.
In between the Indus and the Gangetic systems in the north and the Vindhya mountains on the south lies a vast stretch of land, which is divided into two units by the Aravali mountains. The area west of the Aravali is covered by the Tharp desert, although a part of Rajasthan also lies in this region. The south-eastern portion of Rajasthan has been a comparatively fertile area since ancient times.
Rajasthan shades off into the fertile plains of Gujarat, which are drained by the waters of Narmada, Tapti, Mahi and Sabarmati.
South of the Ganga-Yamuna doab, and bounded by Chambal river on west, Son river on east, and the Vindhya mountains and Narmada river on south, lies the state of Madhya Pradesh. Its northern part consists of fertile plains.
The great Brahmaputra originating fron\ the eastern part of the lake Mansarover in the Kailash flows eastward through the plateau of Tibet under the name of Tsangpo. Then it turns south and enters in India where it assumes the name Dihang.
Later, the rivers Dihang and Lohit join and are called Brahmaputra or Lauhitya. Passing through Assam and Bengal it joins the easternmost mouth of Ganga. But before falling into the Bay of Bengal another mighty river, Meghana, joins it. The delta thus formed is one of the most fertile part of Bengal and is known as Sundarban delta.
Except the Narmada and the Tapti, which run towards west and join the Arabian sea, all the rivers of the Peninsular India run from west to east. Most of them rise from the Western Ghat and traversing the whole breadth of the plateau, fall in the Bay. Mahanadi forms a broad plain known as the Chattisgarh plain in the north-east.
It passes though Orissa before joining the sea. The valley of Godavari with its tributaries has a large flat land in the north but it narrows in the east before meeting the sea. Further south, Krishna, with its tributaries like Tungabhadra, divides the Deccan plateau into two sections. Further south, Kaveri and its tributaries form another important river system.
One thing should be mentioned here that these rivers are different from those of the north India. Devoid of a perennial water source like the Himalayas, these southern rivers are mostly dry during the hot reason, hence less valuable for irrigation and navigation purposes.