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UNDP Climate Change Country Profile: Ghana
Document Type:Oxford Climate Data
Document Author (other):and G. Lizcano, C. McSweeney, M. New
Publication Date:2008 October 30
Ghana is located in West Africa on the Guinea Coast. At latitudes of 4‐12°N, the climate of Ghana is tropical, and strongly influenced by the West African Monsoon.
The rainfall seasons of Ghana are controlled by the movement of the tropical rain belt (also known as the Inter‐Tropical Conversion Zone, ITCZ), which oscillates between the northern and southern tropics over the course of a year. The dominant wind direction in regions south of the ITCZ is south‐ westerly, blowing moist air from the Atlantic onto the continent, but north of the ITCZ the prevailing winds come from the north east, bringing hot and dusty air from the Sahara desert (known as the ‘Harmattan’). As the ITCZ migrates between its north and south positions over the course of the year, the regions between these those northern and southernmost positions of the ITCZ experience a shift between the two opposing prevailing wind directions. This pattern is referred to as the West African Monsoon. In northern Ghana, there is a single wet season occurring between May and November, when the ITCZ is in its northern position and the prevailing wind is south‐westerly, and a dry season between December and March when the ‘Harmattan’ wind blows north‐easterly. The northern and central regions receive 150‐250mm per month in the peak months of the wet season (July to September). The southern regions of Ghana have two wet seasons, one in March to July, and a shorter wet season in September to November, corresponding to the northern and southern passages of the ITCZ across the region.
The seasonal rainfall in this region varies considerably on inter‐annual and inter‐decadal timescales, due in part to variations in the movements and intensity of the ITCZ, and variations in timing and intensity of the West African Monsoon. The most well documented cause of these variations is the El Niño Southern Oscillation (ENSO). El Niño events are associated with drier than average conditions in West Africa.
Seasonal variations in temperature in Ghana are greatest in the north, with highest temperatures in the hot, dry season (AMJ) at 27‐30°C, and lowest in JAS at 25‐27°C. Further south, temperatures reach 25‐27°C in the warmest season JFM, and 22‐25°C at their lowest in JAS.