Northeast India displays, to a
large extent, the character of a tropical climate, especially in the valleys. The
region has a monsoon climate with heavy to very heavy rains, confined to
four summer months from June to September. The southwest monsoon is the main
source of rain, and June is the rainiest month.
Climate Characteristics of Northeast India
There are three seasons in the
area, winter, summer, and rainy season, though the rainy season, as in the rest of
India coincides with the summer months. There is a climatic contrast between the
valleys and the mountainous region. While the mean January temperature in the
valley region of Assam is around 16 °C, the temperatures in the mountainous
region of Arunachal Pradesh and Nagaland hover around a maximum of 14 °C and a
sub-zero minimum temperature.
The summer temperatures in the plains vary
between 30 and 33 °C, while the hills have a mean summer temperature of around
20 °C with a mean minimum of 15 °C. Nowhere in the region, there is heavy snow
except in the higher parts of Arunachal Pradesh, like the west Kameng and Tawang
areas.
No part of North-East India receives rainfall below 1,000 mm. Shillong
plateau with its southern limit marked by a 1,200-m-high scarp overlooking the
Bangladesh plain receives very heavy rains. Cherrapunji, situated on the top of
the scarp receives a mean annual rainfall of 11,465 mm.
The average rainfall
of Brahmaputra valley is around 2,000 mm with local variations. Guwahati, being
in the rain shadow of the Meghalaya plateau, receives only 1,717 mm of rain.
About 90 % of the rain is received during the southwest summer monsoon, and
June is by far the rainiest month.
The hilly areas of the region receive
2,000–3,000 mm of rain, though places like Kohima in Nagaland and Imphal in
Manipur, because of their being in the shadow of the mountains, receive less
than 2,000 mm of rain (Dikshit K.R., Dikshit J.K).
Types of Climate Found in Northeast India
1. Cloud, Humid, High, Altitude Climate:
This type of climate prevails over the mid-northern part of Arunachal Pradesh and the eastern hills in the area above 2000m. The temperature is generally low over here, with the lowest touching point below 00c in winter, and the highest not exceeding 200c even in the hottest month. Precipitation is high, coming sometimes in the form of snowfall. Average annual precipitation is above 150 cm. since this includes the mountainous areas, agricultural facilities are limited. Some amount of hill-rice maize, millets, and vegetables are grown on the hill slope.
2. Humid sub-Tropical Monsoon Climate:
This type of climate prevails over the Arunachal Foothills bordering the Brahmaputra Valley, Nagaland, the Eastern Part of North Cachar Hills, Manipur and Mizoram. The temperature in this region is higher than in the previous region but lower than in the plains, average annual being 100c-200c. The summer is sufficiently hot and humid, while winter is longer and drier than in the plains.
3. Hot, Humid Monsoon Climate:
This region's type of climate prevails over all the plains area and the northern foothills of Meghalaya. The temperature over here is generally higher, with summer maximum reaching 360c and winter minimum hardly going down to 100c. Rainfall is high, the average annual rainfall amount being above 150 cm and reaching 300 cm in many places. The relative humidity is high for about 9 months of the year.
4. Rainy, cool Monsoon Climate:
This type of climate prevails over the higher southern half of Meghalaya to the south of a line joining Darugiri, Nongkhlaw, Umsing and Hamren of Karbi Anglong. This area is characterized by low temperatures (lower than 200 C) even in summer and 00c in winter throughout the year and with rainfall occurring for about 8 months. The amount of average annual rainfall is over 250 cm. It is this area that supports the rainiest places like Mowsynram. Common crops grown are hill rice, rice, maize, millet, and vegetables. It also supplies such fruits as apples, oranges, pears, apricot, pine, etc. The area has a natural pine forest.
5. Alpine Climate:
The alpine climate prevails over the high Himalayan region along the northern part of Arunachal Pradesh. The region has a cold climate throughout the year with the temperature remaining below 00C for a long in winter. Cold mountain wind, which often turns into a blizzard, is a common phenomenon here. Precipitation occurs in the form of snowfall in winter.
Rainfall is only occasional in summer. As the ground in the area of this climate remains frozen and as summer rainfall is insufficient, the natural vegetation is confined to alpine grasses, short bushes, junipers and stunted conifers. Barely and oat are grown in the sheltered valleys, while yak and mules are domesticated beasts of burden in the region.
Source
Dikshit K.R., Dikshit J.K. (2014) Weather and Climate of North-East India. In: North-East India: Land, People and Economy. Advances in Asian Human-Environmental Research. Springer, Dordrecht
Taher M.,Ahmed P., geography of northeast india, Mani Manik Prakash, Guwahati