A fragile sub-Himalayan ecosystem

The North-eastern region of India including Assam with its peculiar bio-geographical location, marked with rugged and high hills to low alluvial plains and dominated by a wide variety of forests, grasslands, swamps and flood-plains exhibits a spectacularly unique bio-diversity.

This region is the original home of many of the wild varieties of rice, citrus, mango and bamboo and medicinal plants. The genetic diversity of its flora is accompanied by a wide range of diversity of its faunal resources. The region is now recognized as one of the eighteen identified ‘hot spot’ areas of the world for its high concentration of bio-diversity with particular reference to the threats faced by many valuable species of its rich flora and fauna. Growing urbanization, industrialization and human settlements, wanton destruction of forests, improper land use including unscientific shifting cultivation practices, commercial greed and poaching, besides natural calamities of floods, earthquakes and landslides etcetera have caused severe erosion to our genetic resources.

It is necessary that urgent measures and policy initiatives are taken to conserve and propagate the region’s valuable endemic genetic resources, both flora and fauna, that are threatened and rare, and further promote such schemes which will enable our environmental resources to develop as valuable economic assets for the people. In this context that in medicinal plants alone, the North-eastern region can have a substantial share in the international market to the tune of several crores of rupees, provided appropriate steps including application of modern technology are taken for conservation and propagation of these plants in the region.

For the purpose of protection of this gene-rich area, the approach should be on a regional basis rather than on confining ourselves to a particular state. The North Eastern Council, it is hoped, will take a leading role in forming a multidisciplinary Task Force to address to the region’s various issues on bio-diversity conservation and in organizing special training programmes for core groups of scientists on modern concepts of conservation of nature and bio-diversity.

Climate of Northeast India: A brief description

It has been observed that the classification of climate of Northeast India according to both ‘Thornlhwaile's and Koppen's methods’ are found to be defective because of the exclusion of the local characteristics.

Due to peculiar physiographic make up of the region and ineffective Northeast Monsoon, the climate of different parts of the region has assumed regional and local characteristics. As a part of South East Asia, the climate of the Northeast India is obviously Southeast Asiatic Monsoon. In this region the hills are irregular in their exposition with inter hill valley plains. The regional orographic structure is so varied and different that it seems probable that the weather elements are prominently conditioned locally to produce different climatic characteristics. To evaluate the general climatic personality, the following common factors are taken into account -

1. The alternating pressure cells of North West India, North East India, Bayof Bengal, Indian Ocean, the local depressions and their periodic oscillations.

2. The pre-dominance of maritime tropical air mass (mT).

3. The moving periodic western disturbance, and

4. The local mountains and valley winds.

Along with these factors the influences of the regions extensive water bodies, forests and local storms cannot be neglected. The border of the region is surronunded by ranges of hills; and there is a possibility that the mountain topography of the region exerts both mechanical thermodynamics influences on the general and seasonal circulation of winds, distribution of pressure, temperature and precipitation.

The months of February, March, April and May constitute the pre-monsoon season in Northeast India. From the month of February, the land surface is steadily heated and the temperature rises. Local depressions are formed over Brahmaputra plain where strong convection develops especially in the afternoon hours of the day and with a slow pace a stormy weather follows. In the lower Brahmaputra valley, strong Northeast wind rises dust from dry river banks. Ice over the lofty northern and eastern hills melts and this melting ice supplies moislure and potential energy for development of thunderstorms.

The "Norwesters", locally called "Bordoichilla" start moving during this period. The "Norwesters" move to the north east by the second week of April and by the first week of May it takes western movement. During the pre-monsoon period rainfall ranges between 60 cm and 85 cm, and the temperature ranges between 19°C and 36°C. The pre-monsoon season is in fact a transitional phase between dry cool winter and warm moist monsoon.


State wise climatic distribution

The Mountain ranges of Arunachal Pradesh are the wettest part of eastern Himalaya, which records an annual precipitation of 3000mm is being common in Kameng. And over most of the region there is rarely less than 1000 mm.

In the northern portion of Arunachal Pradesh a large proportion of the precipitation comes in winter than in the southern portion where there is still rainfall is maximum in summer. In winter there may be snow on the Kangto and some of the northern most Namcha Barwa. A notable feature of the climate of northern Arunachal Himalaya is a very high temperatures experienced in summer in the deep sheltered valleys of Dibang, bang, where the thermometer occasionally registers 250C. At Along, for instance, the temperature ranges from an average of 1O°C in January to 32°C in June, the hottest month and has an annual rainfall of 2000mm, three quarters of which comes in summer quarter of the year, Passighat on the right side of Brahmaputra valley, recorded high temperatures, average ranges being from 5°C in January to 28°C in June, Rainfall in Passighat is about 2250mm annually.

Tripura is the state, which is traversed by the Tropic of Cancer, the heat is comparatively great in all seasons except in winter. The heat creates a constant humidity of moisture laden air from the Bay of Bengal, which is cooled by its constant rise upwards. The tendency of hot air to rise is also promoted by the local hills and "tillas" of the state. As the air rises, the moisture contained in it is condensed and hence the state has the state records heavy rainfall. The southern tip of Tripura is 150 Km far from the shore of Bay of Bengal. Near the seashore and Tropic of cancer rainfall is recorded almost once a month after rainy season. The average annual rainfall is about 2000mm, received mostly in the monsoon months between June and September. The maximum temperature is in the month of April 34.4°C and minimum being 5.7°C in January.

The Manipur state lies within the monsoon area and its rainfall is very regular and heavy. The valley of Manipur and hills receives their largest rainfall in the summer by the south - west monsoon winds. July is the wettest month in the state. The configuration of the valley make available much damages from floods; the vast volume of water which occasionally sweep down the river channel causing intense damage to life and property. These floods are generally very sudden and have been known to rise to a great height in the state (Negi, 1989). In the upper high lands of Manipur heat is never intense, the mean temperature at Imphal in July being only 28°C, except at Bishenpur, the diurnal range is highest in November.

The climate of Meghalaya is characterised by coolness and extreme humidity. The natural sytem of the water surface and extensive forests over which evaporation and condensation process takes place and the close proximity of Bay of Bengal, may be some of the reasons for the excessive precipitation takes place in Meghalaya. The total amount of rainfall in Meghalaya during the year is always abundant but is sometimes unequally distributed. In Surma valley the average rainfall is 2500 mm. To the south of the valley precipitation is less pronounced, but there is torrential rain on the southern slopes of the Khasi Hills and the water is poured down into the valley below. The average annual rainfall at Cherrapunji is in 12000mm, but sometimes it is more than the average. There is no other station in Indian subcontinent where the recorded rainfall is as heavy as at Cherrapunjii on the Southern slopes of Khasi Hills. The Bay of Bengal branch of monsoon strikes the Arakan coast and then passes on into funnel shaped formation of the Garo Khasi hills. The ascent of these moisture laden currents in this funnel gives Cherrapunji the highest rainfall of the world, but the clouds are rapidly drained of their moisture and at Shillong, which is less than 48 kilometers away it is only 2150mm. At Jowai, which lies at about the same distance south east of Shillong, the average annual rainfall is 5000 mm. The rainfall has never been recorded in the northern hills, but it is probably between 1600 to 1800mm (Negi, 1989). On the Shillong plateau the temperature seldom rises above 160C in the hottest season of the year.

The climate of Nagaland is generally cool, at Kohima the temperature rises above 15°C. The high hills are healthy, but during rains the valleys and the lower ranges are decidedly malicious. The monsoon cause the rainfall on the east to be very heavy at all seasons. The rainfall occurring mostly between warmer months from April to October ranges between 1700mm to 2000mm. The rainfall is heaviest on the Western and Southern slopes of Nagaland. At Kohima it is 1500 mm in the year but further north at Woklia and Tamlu, it exceeds 2000mm.

The Tropic of Cancer runs through the heart of Mizoram, Because of considerable variations in attitude, the region has a pleasant climate. It gets heavy rain between May and September. The Monsoon rainfall begins in May and owing to the accessional motion of the monsoon current, caused by the Mizo Hills, is heavier throughout the season than in any other inland tract of Bangladesh. The rainfall is 300mm in May and 510mm in June, July after which it slowly diminishes to 270mm in September, the average rainfall for the year is 2000 mm. Though floods may occur in any monsoon month, very heavy precipitation occurs either early or late in the season, being due to depression from the Bay of Bengal which break up on reaching the Assam Valley. But winters are rain free and very pleasant. There is a fascinating variety of landscape to which the Blue sky and Green Hills lend their own charm. The temperature changes but little between April and October; the average maximum falls from 280C in April to 250C in October; while the highest average minimum is 180 in July, August and September, however, the mean is almost constant at 200C.

The climate of Assam is humid and hot. In the hot season the sky is cloudy and the persistent rainfall takes place, which prevents the land from becoming hot and dry. During the rainy season, only the river banks and the artificial mounts on which habitations are situated escape inundation. Assam is unique for its uniform temperature and high humidity prevailing from April to October. The mean minimum temperature remains almost stationary between 180C and 190C from April to September, but falls in the cold season to 150C. The annual average rainfall is 1500mm.