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climate & vegetation

Climate

 

The Accra Metropolitan Assembly lies in the Savannah zone. There are two rainy seasons. The average annual rainfall is about 730mm, which falls primarily during the two rainy seasons.

The first begins in May and ends in mid-July. The second season begins in mid-August and ends in October. Rain usually falls in intensive short storms and give rise to local flooding where drainage channels are obstructed.

There is very little variation in temperature throughout the year. The mean monthly temperature ranges from 24.7°c in August (the coolest) to 28°c in March (the hottest) with annual average of 26.8°c.

As the area is close to the equator, the daylight hours are practically uniform during the year. Relative humidity is generally high varying from 65% in the mid-afternoon to 95% at night. The predominant wind direction in Accra is from the WSW to NNE sectors. Wind speeds normally range between 8 to 16 km/hr. High wind gusts occur with thunderstorm activity, which pass in squall along the coast.

The maximum wind speed record in Accra is 107.4 km/hr (58 knots). Strong winds associated with thunderstorm activity often cause damage to property by removing roofing material. Several areas of Accra experience micro climatic effects. Low profile drainage basins with a north-south orientation are not as well ventilated as that orientated east west.

Air is often trapped in pockets and an insulation effect gives rise to local increase in air temperature of several degrees. This occurs in the Accra Newtown, sports complex areas.  

Vegetation

 

There is evidence to suggest the vegetation of the metropolitan areas has been altered in the more recent past century by climatic and other factors. Much of the metropolitan area was believed to have been covered by dense forest of which only a few remnant trees survive.

A climatic change combined with the gradient of the plains and cultivation has imposed vegetational structures similar to those of the southern shale, Sudan and Guinea Savannahs all of which lie north of the Accra plains.

There are three broad vegetation zones in the metropolitan area, which comprise shrub land, grassland and coastal lands. Only the shrub land occurs more commonly in the western outskirts and in the north towards the Aburi hills.

It consists of dense clusters of small trees and shrubs, which grow, to an average height of five metres. The grasses are a mixture of species found in the undergrowth of forests.

They are short, and rarely grow beyond one metre. Ground herbs are found on the edge of the shrub. They include species, which normally flourish after fire.

The coastal zone comprises two vegetation types, wetland and dunes. The coastal wetland zone is highly productive and an important habitat for marine and terrestrial-mainly bird life.

Mangroves, comprising two dominant species, are found in the tidal zone of all estuaries sand lagoons. Salt tolerant grass species cover substantial low-lying areas surrounding the lagoons.

These grasslands have an important primary production role in providing nutrients for prawns and juvenile fish in the lagoon systems. In recent times, wetlands are however being encroached upon. Protection of the coastal wetland zone is very important to the long-term sustainability of the fish industry, which the Ga population of Accra depend upon.

The dune lands have been formed by a combination of wave action and wind. They are most unstable but stretch back several hundred metres in places. There are several shrub and grassland species, which grow and play an important role in stabilising dunes.

Coconuts and palms grow well in this zone, providing protection and an economic crop. Most of the coconuts were panted in the 1920s but it is estimated that over 80% of those plantations have disappeared as a result of felling, disease and coastal erosion. The loss of these trees is one of the principal reasons for the severity of erosion in some areas.

In addition to the natural vegetation zones, a number of introduced trees and shrubs thrive in the metropolitan area. Neems, mangoes, cassias, avocados, and palms are prominent trees on the Accra landscape. Introduced shrubs like bouganvilia are also very prominent. these are being damaged from residential encroachment, bush fire, sand collection and illegal tree felling.

Most of the open spaces in Accra are used for the cultivation of food crops like corn, okro, tomatoes and other vegetables. Fertilizers and insecticides are used in these areas. Constant felling of trees, bad farming practices and annual burning has altered the vegetation from “dry forest” and greatly depleted the fertility of the soil.

Aquatic Vegetation

 

Apart from mangroves and salt marsh grasses, which grow in the intertidal zone, sea grasses or attached algae also occur mainly in rocky areas and wave cut platforms.

These areas have increased as a result of erosion exposing the underlying bedrock - especially to the east of Tema. They have an important role in the coastal ecosystem because of their high rate of primary production in the provision of food and shelter for the survival of shrimps, prawns and many species of fin fishes.

Ocean floor sea gases are confined to a few sheltered areas of the coastline and the lagoons. The ocean floor regime is too unstable to support large areas of sea grass.

Terrestrial Fauna

 

Different species of antelopes, squirrels, monkeys and reptiles live in Accra. Many animals such as the Togob have grass cutter, bush baby and bossman potto are found in the Achimota forest and outside the urbanised area.

Most animals have been pushed inland because for the rapid expansion of settlements in the Metropolitan area. Many species of snakes (some venomous) and lizards are found throughout the Metropolitan area.

Apart from the above-mentioned fauna a great number of domestic animals - donkey, sheep, and goat, chicken are kept domestically in the metropolitan area.

To the north east of Accra on the Akosombo Road lie the Shai Hills. This is a small game park with several of these isolated hills. Several species of monkeys, ground foraging animals and birds inhabit this area.

The Akuapim Hills also provide sheltered habitats for many bird and animal species. The two areas are sparsely populated and generally unsuitable for agriculture use. The long-term prospects of species protection in the Akuapim and Shail Hills are good.

Over 120 indigenous, migratory and exotic bird species have been counted in the Metropolitan area. Wetland species occur mainly in the Densu delta and Sakumo I and II lagoons.

Sakumo II lagoon hosts 10 species of birds of national and international importance. These lagoons could easily be endangered by pollution and is already experiencing adverse impacts from urban development.

Metropolitan bird life is diverse and in spacious residential areas prolific. The many exotic trees planted in the inner city areas provide a suitable habitat for food and shelter, and the lack of predator species has enabled numbers to grow.  

Aquatic Fauna

 

The open lagoon systems support a wide range of crustacean, mollusks, gastropods, predatory and bottom feeding fish. The lagoons are important breeding grounds giving adequate protection against large predator species and a continual supply of nutrients and organisms for food.

The habitat of many of the lagoons is or has been modified by development and increasing levels of pollution. Some species in the lagoons - in particular the Korle lagoon - are no longer suitable for human consumption.

Protection of the water quality and vegetation in the lagoons is important to the long-term sustainability of aquatic fauna along the coastline.

The ocean supports a wide range of pelagic and bottom feeding fish. Common species are grouper, mackerel, cassava fish, African lookdown, sole shark and tiger fish.

Stocks of off shore species have not been depleted mainly because fishing techniques result in a significant loss of smaller fish from nets.

Evidence suggests that on-shore species are nearing exhaustion caused by excessive catches of juvenile and small fish. The loss of this resource will have a substantial impact on the indigenous population of Accra whose livelihood is dependent on fishing.

Weija reservoir, the marshes at the mouth of the Densu River, the Sakumo lagoon near the Panbros salt industry constitute the most important fresh water wetlands for aquatic fauna.

Apart from harbouring a variety of mportant commercial fish species like tilapia and atfish, they also act as breeding grounds for animals, which are adapted to the characteristic coastal Savannah vegetation.



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