and
Eastern Himalaya in Northeast India The Northeast region can be
physiographically categorised into the
Eastern Himalaya, the
Patkai and the
Brahmaputra and the
Barak valley plains. Northeast India (at the confluence of Indo-Malayan, Indo-Chinese, and Indian biogeographical realms) has a predominantly humid sub-tropical climate with hot, humid summers, severe monsoons, and mild winters. Along with the west coast of India, this region has some of the Indian subcontinent's last remaining rainforests, which support diverse flora and fauna and several crop species. Reserves of petroleum and natural gas in the region are estimated to constitute a fifth of India's total potential. The region is covered by the mighty Brahmaputra-Barak river systems and their tributaries. Geographically, apart from the
Brahmaputra,
Barak and
Imphal valleys and some flatlands in between the hills of
Meghalaya and
Tripura, the remaining two-thirds of the area is hilly terrain interspersed with valleys and plains; the altitude varies from almost sea-level to over above
MSL. The region's high rainfall, averaging around and above creates problems of the ecosystem, high seismic activity, and floods. The states of
Arunachal Pradesh and
Sikkim have a
montane climate with cold, snowy winters and mild summers. File:Gangtok ropeway.jpg| File:View of the ridgetop city of Aizawl, state capital of Mizoram.jpg| File:Aerial view of Shillong Meghalaya India.jpg| File:Neer Mahal.jpg| File:The Dzukou Valley.JPG| File:2007-sela-pass-1.jpg| File:Salna Bari, Bhalukpong.jpg| File:2 Loktak lake Manipur India.jpg| File:Majuli Island.jpg| File:Nohkalikai Falls.JPG|
Topography Highest peaks Kangchenjunga, the third highest mountain peak in the world rising to an altitude of , lies in-between the state
Sikkim and adjacent country
Nepal.
Brahmaputra river basin Tributaries of the
Brahmaputra River in Northeast India:
Climate Northeast India has a
subtropical climate that is influenced by its relief and influences from the southwest and northeast
monsoons. The Himalayas to the north, the Meghalaya plateau to the south and the hills of Nagaland, Mizoram and Manipur to the east influences the climate. Since monsoon winds originating from the
Bay of Bengal move northeast, these mountains force the moist winds upwards, causing them to cool
adiabatically and condense into clouds, releasing heavy precipitation on these slopes. It is the rainiest region in the country, with most places receiving an average annual precipitation over , which is mostly concentrated in summer during
the monsoon.
Cherrapunji, located on the Meghalaya plateau is one of the rainiest place in the world with an annual precipitation of . Temperatures are moderate in the
Brahmaputra and
Barak valley river plains which decreases with altitude in the hilly areas. At the highest altitudes, there is permanent snow cover. In general, the region has 3 seasons: Winter, Summer, and rainy season in which the rainy season coincides with the summer months much like the rest of India. Winter is from early November until mid March while summer is from mid-April to mid-October. Under the
Köppen climate classification, the region is divided into 3 broad types: A (tropical climates), C (warm temperate mesothermal climates), and D (snow microthermal climates). The tropical climates are located in parts of Manipur, Tripura, Mizoram, and the Cachar plains south of
25˚N and are classified as
tropical monsoon (
Am). Much of Assam, Nagaland, northern parts of Meghalaya and Manipur and parts of Arunachal Pradesh fall within the warm temperature mesothermal climates (type C) where the mean temperatures in coldest months range from . The entire Brahmaputra valley has a
humid subtropical climate (
Cfa/Cwa) with hot summers.
Temperature Temperatures vary by altitude with the warmest places being in the
Brahmaputra and
Barak River plains and the coldest at the highest altitudes. It is also influenced by proximity to the sea with the valleys and western areas being close to the sea, which moderates temperatures. Generally, temperatures in the hilly and mountainous areas are lower than the plains which lie at a lower altitude. Summer temperatures tend to be more uniform than winter temperatures due to high cloud cover and humidity. In the Brahmaputra and Barak valley river plains, mean winter temperatures vary between while mean summer temperatures are around . The highest summer temperatures occur in the West Tripura plain with
Agartala, the capital of
Tripura having mean maximum summer temperatures ranging between in April. The highest temperatures in summer occur before the arrival of monsoons and thus eastern areas have the highest temperatures in June and July where the monsoon arrives later than western areas. In the Cachar Plain, located south of the Brahmaputra plain, temperatures are higher than the Brahmaputra plain although the temperature range is smaller owing to higher cloud cover and the monsoons that moderate night temperatures year round. In the mountainous areas of Arunachal Pradesh, the Himalayan ranges in the northern border with
India and
China experience the lowest temperatures with heavy snow during winter and temperatures that drop below freezing. Areas with altitudes exceeding receive snowfall during winters and have cool summers. Below above sea level, winter temperatures reach up to during the day with nights dropping to zero while summers are cool, with a mean maximum of and a mean minimum of . In the hilly areas of Meghalaya, Nagaland, Manipur and Mizoram, winters are cold while summers are cool. The plains in Manipur has colder winter minimums than what is warranted by its elevation owing to its geographic location which prevents winds that bring hot temperatures and humidity from coming into the Manipur plain, alongside being surrounded by hills on all sides. This creates
temperature inversions during winter nights when cold air descends from the hills into the valleys below. For example, in Imphal, winter daytime temperatures hover around but nighttime temperatures drop to .
Rainfall No part of Northeast India receives less than of rainfall a year. Areas in the Brahmputra valley receive of rainfall a year while mountainous areas receive a year. The southwest monsoon is responsible for bringing 90% of the annual rainfall to the region. April to late October are the months where most of the rainfall in Northeast India occurs with June and July being the rainiest months. In most parts of the region, the average date of onset of the monsoons is 1 June. Southern areas are the first to receive the monsoon (May or June) with the Brahmaputra valley and the mountainous north receiving later (later May or June). In the hilly parts of Mizoram, the closer proximity to the
Bay of Bengal causes it to experience early monsoons with June being the wettest season.
High-risk seismic zone The North Eastern Region of India is a mega-earthquake prone zone caused by active
fault planes beneath formed by the convergence of three
tectonic plates viz.
India Plate,
Eurasian Plate and
Burma Plate. Historically the region has suffered from two great earthquakes (M > 8.0) –
1897 Assam earthquake and
1950 Assam-Tibet earthquake – and about 20 large earthquakes (8.0 > M > 7.0) since 1897. The
1950 Assam-Tibet earthquake is still the
largest earthquake in India. ==Wildlife==