CLIMATE CHARACTERISTICS OF NORTHERN GHANA. RAINFALLPATTERN

CHANGES OVER TIME.

Northern Ghana (between latitudes 8” - 11 ON), is generally characterised as tropical continental or savannah, with a single rainy season from May to October, followed by a prolonged dry season. The climate of the area is dependent mainly on the movement of two dominant air masses:

l The moist monsoon (or tropical maritime air mass) flowing out of the south west, and i The dry Harmattan (tropical continental air mass) flowing from the north east (Sahara

Desert) direction.

The circulation of the se two dominant air masses regulates the climate of the area. The zone in which the two masses meet is known as the Inter Tropical Convergence Zone (ITCZ). This zone oscillates during the year, following the apparent seasonal movement of the sun between the southern and northern hemispheres. Much of the seasonal rainfall is generated in the belt that lies just south of the ITCZ. The rainfall distribution and amount controls two distinct ecologies, which can be distinguished within the Interior Savannah Zone environment of Northern Ghana, namely the Guinea and Sudan Savannah.

Most of the Northern Ghana falls within the Guinea Savannah Ecological Zone, which is associated with total annual rainfall of about 1 000 - 1 3OOrnm/annum. The rainy season is 140-l 90 days in duration, while the estimated Reference Evapotranspiration (ETo Penman) is about 2 OOOmm/annum, creating a great seasonal deficit every dry season. The peak rainfall period is usually late August or early September. About 60% of the rainfall occurs within the three (3) months (July to September), with torrential rains creating serious drainage problems. In most cases, absorptive capacity of the soils cannot withstand the intensity of the rain, thus creating high amounts of runoff, with erosion being the one of the most significant agricultural constraints in the area. Precipitation considerably outstrips evapotranspiration during the main period of the growing season (July - October).

Sudan Savannah is evident only in the northernmost part of the country. The total rainfall in this area is below 1 00Omm/annum. The rainy season is between 110 - 140 days in duration, with high evapotranspiration losses in the dry period.

The vegetation typical of Northern Ghana consists of mixed formations of fire resistant trees and shrubs. Moving northwards, within the Savannah region, there is at first densely wooded and vigorous grassland (Andropogon spp.), with fire resistant shrubs, oflen referred to as a woodland Savannah.

Further north, at the transition between the Guinea and Sudan Savannah, woodland Savannah gradually gives way less wooded tree Savannah. Still further, in an increasingly arid environment, grass Savannah is formed, with trees and shrubs either absent or very sparse.

The evidence of climatic trends and changes in Ghana was firstly presented at the National Workshop on Climate Change in Accra, in 1993. In study carried out by Ontoyin, Y., (1993), 1961- 1990 average temperatures were compared with those from 193 1 - 1960 for about 11 synoptic stations in Ghana. The temperatures were on the rise during 1961- 1990 period, in all but two of the observed stations. The stations in the northern part of the country (namely Wa, Navrongo, Tamale and Yendi), all show an increase in the average daily temperature for the last thirty years, as compared to data recorded from 193 l-1 960.

Annual rainfall for seven (7) stations in Northern Ghana was also analysed as a part of the current presentation. Time series range from 65years (the longest available unbroken records, recorded

1bU

According to data presented in the Table l., three (3) of the observed stations display clear decreasing trend. Among these is the station with the longest unbroken records of 65 years (i.e., Navrongo).

However, station with the second longest unbroken records (Tamale, 60 years of data) shows

slight incw of annual rainfall for the period. The annual rainfall records obtained from the remaining three (3) stations used for the study show variable behaviour, increasing or decreasing without clear distinction regarding latitude, altitude, or agro-ecological zone.

It is therefore difficult to firmly conclude if the rainfall in Northern Ghana is generally declining, as was stated in the temperature study fhtoyin, 1993). It is only clear that, with the increasing temperatures, climatic water balance is going to be even more unfavourable for the agricultural production. Influence of human factors cannot be neglected in this fragile system, since population pressure is high in some parts of Northern Ghana, especially those with the least rainfall (i.e., Manga, Navrongo, Bolgatanga), exceeding 240 persons/km2.

3.0 TRADITIONAL FARMING SYSTEMS IN NORTHERN GHANA.

GOVERNMENT POLICIES AND INFLUENCE OF NON-GOVERNMENTAL

ORGANISATIONS.

Indigenous farmers in the region under study usually classify soils according their location in the topography. The classification distinguishes between the soils on uplands, the transition and the lowland or valley bottom soils. They go further to identify certain crop species with the soils on which they grow best. Thus, cereals, such as millet, sorghum or maize are farmed on upland soils, deep rooted crops like yam or cassava in the transition zone, and rice and water tolerant crops on the valley bottom soils. The names of soils in the traditional farmers’ classifications are different for each ethnic group in the area, and have been mostly incorporated in the official classification systems.

The development of land preparation and conservation methods is based on past experience of changes in biophysical environment. The following are most common methods used in the study region:

l Broad Beds. They are generally staggered in various directions to reduce the effect of water erosion. These beds are frequently planted with groundnuts, and in some cases with millet or sorghum, in which case their height is adjusted. Broad beds are usually constructed on transitional soils.

l Stone Bunds - Terrace System. This method is used in places with slopes of about 10% and rock outcrops on the surface, which are common in the study area. Recently, this traditional conservation method has been improved with contributions from non-governmental organisations (NGOs) working in the area, which are training farmers to identify contour lines and place stone bunds along them. The usual crops sown on the terraced fields are millet, sorghum, beans and groundnuts.

l Mounds. Their size and shape vary with their topographic position along the slope. The upper slope mounds are smaller and usually cropped with millet, sorghum, and sometimes groundnuts.

Those located on the middle slopes are about 30cm high, with about 50cm diameter at the base.

On the lower slopes with heavy textured soils, the mounds are about lm high, with a base of about 1.5m in diameter. The lower slope soils are subject to water logging during the rainy season, and the larger size of the mounds ensures better drainage. Some mounds are semi-circular in shape, and placed at the boundaries of farmer’s field to trap runoff water and enhance water availability during

check soil erosion, while for excessive runoff, ridges along the slope serve to drain away any exceeding water. In some cases, ridges can be enclosed in a bund system.

l Basins. Basins are usually constructed in the valley bottoms of inland valleys. They are mostly of irregular shape, made by hand hoe, using available soil, which is usually clay loam. During rainy season the basin edge is reinforced, using uprooted weeds. Rice is the main crop in basins, followed by sorghum. A second crop can sometimes be produced, using residual moisture after the rice has been harvested.

In addition to mechanical protection against erosion, mixed cropping is traditionally used to ensure higher food security. This involves planting crops of different rooting depths on the same piece of land to reduce competition for nutrients and water.

Planting groundnuts on flat lands is also practised as agronomic measure providing surface cover against erosion. Other crops used for the same purpose include local varieties of creeping cowpea.

Strip cropping with Andropogon spp., is sometimes used to reinforce ridges or in between the stone bunds to reduce soil erosion. This technique has also been modified by some NGO’s present in the area, and grass strips are planted following contour lines.

Traditional methods of maintaining soil fertility are also widely practised. They include, among others:

- inter-cropping cereals with legumes;

- incorporation of weeds in mounds;

- use of manure and household wastes (especially on the farms close to compounds);

- pseudorotation;

- utilisation of crop residues;

- short-term land fallow, etc.

Permanent damage to the environment, caused by various farming activities, both traditional and modem, can be reduced, and in some cases altogether avoided through research programmes combined with education and training of farmers. Current policy of the Government of Ghana is oriented towards responsible use of the environmental resources. The concepts summarised by the Environmental protection Council are fundamental to agricultural development as outlined in the strategies for agricultural growth set out by Ministry of Food and Agriculture (MoFA) in Medium Term Agricultural Development Plan WTDAP, 1990). A policy has been proposed to reduce constrains imposed by soil erosion, degradation of soil physical characteristics, and limited moisture availability.

The implementation strategy revolves around the promotion of sound farming systems instead of placing emphasis on the construction of physical conservation works, as it was done from 1960s to 1980s.

Although there are critical areas, which may require physical works to reduce erosion, the emphasis is on extension advice to the farmers to promote and improve already existing conservation systems.

However, this policy recognises the major agricultural constraint posed by rainfall unreliability typical for this part of the country. This makes it difficult to quantify the impacts of dry periods on yields, and consequently to define a cost-effective strategy for moisture conservation. As a way to resolve this issue, the policy seeks to give high priority to completion of necessary climatic analysis and to undertake trials with a view to establish whether the improved traditional techniques of moisture conservation are acceptable as a tool in the current socio-economic environment of Northern Ghana.

In this situation, it is not surprising that many non-governmental organisations work on the improvement of conservation systems in the study area. They are organised in four (4) broad groups, or networks, which enable them to collaborate with each other. The broad groups in the region are

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Northern Ghana Network for Development, with approximately 44 grass-root non-governmental organisations as its members, Low External Input Sustainable Agriculture &EISA) group, with 11 members, Association of Church Development Projects/Agricultural Information Service (25 members), and other 13 organisations which are not formally organised. All these organisations are engaged in soil and water conservation activities. Their scope vary from fund mobilisation through creation of environmental awareness in rural communities to watershed management initiatives such as tree planting on demonstration fields or video shows and exchange visits to communities within or outside country.