Orissa extends from 17-degree 49 N to 22-degree 34N latitude and from 81-degree 27-E to 87-degree 29’ E longitudes on the eastern coast of India. It is bound by the States of West Bengal on the North-East, Jharkhand on the north and Chhatisgarh on the West, Andhra Pradesh on the South and Bay of Bengal on the East.

Morphologically Orissa can be divided into five parts. The coastal plains, the middle mountainous country, the rolling upland, the river valleys and the subdued plateaus.

The coastal plains of Orissa stretch from the Subarnarekha in the North to Rushikulya in the South. They are narrow in the North, widest in the middle, narrowest in the lake Chilka coast and broad in the South.

The coastal plains are the gift of six major rivers, which bring silt from their catchments. The rivers from North to South are the Subarnarekha, the Budha Balanga, the Baitarani, the Brahmani, the Mahanadi and the Rushikulya.

The coastal plains can be termed as a land of ‘six deltas’ of the Subarnarekha and the Budha Balanga, the middle coastal plains the combined deltas of the Baitarani, the Brahmani and the Mahanadi and the South coastal plains (The Rushikulya plains).

The mountainous region of Orissa covers about three-fourths of the area of the State. This region is a part of Indian peninsula. Here deep and broad valleys are cut by the Baitarani, the Brahmani, the Mahanadi, the Rushikulya, the Vansadhara and the Nagavali rivers. They are fertile, well-drained and thickly populated. Morphologically this region can be divided into the following units:

(a) the Simulia and the Meghasan mountains,

(b) the Baitarani and the Brahamani interfluous,

(c) the water shed between the Brahmani and the Mahanadi,

(d) the water shed of Rushikulya and the Vansadhara.

The elevation ranges from 610 to 1, 068 meters. The rolling uplands are lower in elevation than the plateaus. They vary from 153m. to 305m. They are the products of continued river action, are rich in soil nutrients, and are situated in the Koel-Sankh basin of the upper Brahmani in the Ib, the Suktel and the Tel of the middle Mahanadi and the Sabari basins. The rolling uplands may be grouped as follows : the Rajgangpur uplands, the Jharsuguda uplands, the Bargarh uplands, the Balangir-Titilagarh-Patnagarh uplands, the Bhawanipatna uplands, the Malkangiri uplands and the Rairangpur uplands.

River valleys are net product of the action of rivers. They are fertile and at times present an undulating topography. The major river valleys of Orissa are associated with the Brahmani, the Mahanadi and the Vansadhara rivers.

The subdued plateaus (305–610m.) reveal all the peculiarities of peninsular tablelands. They are almost flat and the monotony of topography is interrupted by the river valleys. These features are commonly met within the upper Baitarani and the Sabari basins of the Keonjhar and Koraput districts, respectively. In these uplands sheet erosion is most common while gulling is confined to the river valleys. These plateaus can be divided into the Panposh-Keonjhar-Pallahara plateaus and the Nawrangpur-Jeypore plateaus.

Climate

Orissa enjoys a tropical monsoon-type climate like most other parts of the country. Its annual average rainfall is about 200cm. The south-west monsoon normally sets in between July 1 and July 15 in the entire state. By October 15, the south-west monsoon withdraws completely from Orissa. Orissa is not directly influenced by south-west monsoon branch from the Bay of Bengal like the west coast, but the annual cyclones from the Bay of Bengal influence it and bring rains with two seasonal peaks, July-August and October-November. During the winter, except Northern Orissa, all other parts remain almost dry.

Rainfall

Monsoon rainfall is of highest importance as it directly controls the crop condition in Orissa. Monsoon rainfall is considered 'high' when it is above 140cm and 'low' when it is less than 120 cm as this is barely sufficient for a good paddy harvest. Winter rainfall helps the growth of the second crop in Orissa. A total rainfall of above 5 cm during the winter has been taken to be 'high' while less than 2.5cm is 'low' in Orissa.

Cyclones

Flood and drought are common features in the State. Cyclone has in recent years become a regular feature like flood and drought. The cyclonic storms during the monsoon which originate in the Bay of Bengal often cross the east coast between Paradip and Chandbali and make a north-west ward journey. They proceed over Kendujhar and head towards Sambalpur and then weakens. There are two cyclonic peaks in their occurrence, one during May-July and the other during October-November. As far as the periodicity of the storms, the maximum number of cyclones occur during south-west monsoon period (154) followed by the post-monsoon period of the north-east monsoon (70) and pre-monsoon period (57). Orissa experiences three main seasons, but the year is locally divided into six seasons.

Environmental Degradation

Orissa is facing environmental degradation due to large-scale deforestation over the past few decades. The forest-cover of nearly 37 percent of the total area is divided into four parts. 1) Dense forest, 2) Sparse dense forest, 3) Tidal forest, and 4) Almost devoid of trees and fallow forest land.

Environmentally sound forest helps maintain the ecological balance. The drastic denudation of forests is primarily due to unauthorised felling, forest fires, fast growing cattle population, unauthorised overgrazing, encroachment on forest land for sedentary peasant cultivation, shifting cultivation and population explosion. This has resulted in a reduction in rainfall, heavy increase in the frequency of floods and droughts. Top soil is eroded as a result of shower, filling up the artificial reservoirs and river beds downstream, reducing the rate of percolation. Consequently, wells, springs and other water bodies dry up.

The huge cattle population does not allow under-growth to thrive. Seeds are spoiled and new germination takes place. Consequently, the shrubs are reduced to pastures. The population increase has also played its part in environmental degradation. The human, need tonnes of fuel wood for cooking and for factories. Hence, the firewood needs have to be met through social forestry.

The tribal population practicing shifting cultivation on an extensive scale endangers direct loss of valuable forest cover. This massive deforestation has resulted in environmental degradation in an acute form, the results of which are felt on reservoirs, like the Hirakud and lakes like Chilka which are being silted up rapidly.

The silt deposit in the Hirakud is increasing year after year. According to the Orissa Remote Sensing Application Centre, if this situation continues unchecked, by 2065, 460.3 million acre feet of slit will be deposited in the reservoir which is about 70.2 percent of the dead storage capacity level. All this is the direct result of deforestation.

The largest brackish water lake in India is facing environmental disaster. Due to the massive deforestation in the upper reaches of the Mahanadi and in the eastern Ghats, it is being silted up rapidly. Due to silting in the north-east and north-west sectors of the lake, the average depth of Chilka has reduced. Apart from this, its 31 km long channel from Magarmukh to Arkhakud where it meets the Bay of Bengal has been choked up by innumerable islands of varied sizes and sand-dunes from the Bay of Bengal. The choking of the mouth obstructs the outflow of water from the lake and also the inrush of tidal sea water. This has decreased salinity of Chilika water.

A large number of illegal migrants from Bangladesh, who settled on the northern shore of the lake, use fishing nets of fine mesh causing decline in prawn and other fish varieties and crabs. In fact, the fish catch has declined due to over harvesting. More than 158 fish species are facing extinction. Partial restriction of prawn catch during breeding time (Sep-Dec) is one of the solutions to the problem. Restriction of fishing inside the lake is another solution. Reduction in salinity is adversely affecting the aquatic life in the lake.
A large number of avifauna (birds) visit the lake during winter. But, now the number has declined due to the lack of any perching ground.  Weed lands are fast being silted up and being converted into marshes.

The Similipal Tiger Reserve Area has also suffered heavy deforestation due to shifting cultivation of the tribes who live inside the bioshphere and also due to large-scale unauthorised felling of trees in deep forests.

Natural Vegetation

Forests are largely controlled by rainfall and temperature conditions of the region. Forests cover nearly 37 percent of the total area of the state. Mal-distribution forest resources poses a serious problem in the state. The fertile coastal plains with a dense population lack forest cover. Besides, the presence of large tribal population practicing shifting cultivation on an extensive scale causes direct loss of valuable forest cover.

Geographical Classification of Forests

The Northern Tropical Semi-Evergreen Region: This area is composed of a dense tree growth 24-36 meters high. The most striking feature of this region is the absence of bamboo growth. The tropical semi-evergreen forests are concentrated around Bonai between the Champajharan Pass and the Kurapadi stream of Bhagat Pass. They are also seen in the Redhakhol region because of its elevation and precipitation.

The Northern Tropical Moist Deciduous Region: This region accounts for almost 80 percent of the total forest cover in Orissa. The Sal woods dominate this region along north and north-east of the river Brahmani. It is also found to the east of Tel river and in the Sabari basin. (Sal is the most valuable timber of Orissa). The Dendrocalamus stricts (Salia baunsa) and Bamboosa arundinacea (Kanta baunsa) are the two dominant species which are found in the forests of the Eastern Ghats. They are confined to the Mahanadi and Rushikulya basins. The heterogeneous deciduous zone is the meeting ground of the Sal and other species like Adina Cardifolia (Kusum), the Xylia Xylocarpa, the Anogeissus Iatifolia (Dhau) and the Machilusvilloso.

The Northern Tropical Dry Deciduous Region: The dry deciduous type is confined to the upper Tel, upper Nagavali and upper Sabari basins in the Western and South-Western parts of Orissa. Here Sal and Bamboo trees thin out and teak pre-dominates.

The Coastal Forests: The dense growth of palm and coconut with long thin stems, deep roots and a thin crown, has adapted itself nicely to the severe cyclones from the Bay of Bengal during the pre and post-monsoon periods. Creepers of varied species and canes and other minor types of trees have led to the description of the tidal forests of the Mahanadi mouth as the 'Little Sunderbans'. On the Puri coast, casuarina plantation has met the town's demand for fuel. In between the mangrove forest and the cultivated zone a narrow strip of grassland extends from Chilka lake to the mouth of the Mahanadi and beyond.