Abstract
The socio-economic sector of West African countries is rain-fed agriculture driven. Information regarding the onset, cessation and duration of the rainy season is thus, very essential. In this paper, a comparison of the onset, cessation and duration of the rainy season has been carried out using simulated rainfall data from the fourth generation Regional Climate Model (RegCM4) and rain gauge measurements from Ghana Meteorological Agency (GMet), covering a period of 1998 to 2012. Similar onset and cessation dates were seen in both the simulated and guage rainfall measurements for the various agro-ecological zones, resulting in similar duration of the rainy season. The average duration of the rainy season were less than 200 days for the savannah and coastal zones whereas the duration of the rainy season were beyond 200 days for the forest and transition zones. The bias of these comparisons was less than 30 days and the root mean square error (RMSE) values were less than 15 days for all stations, except Saltpond. The Pearson’s correlation (r) typically ranged between 0.4 and 0.8. However, negative correlations were observed for Tamale in the savannah zone, and the entire coastal zone. These findings are indications that RegCM4 has the potential to clearly simulate the movement of the rain belt, and thus, could fairly determine the onset, cessation and duration of the rainy season. The findings have significant contributions to effective water resource management and food security in Ghana, as the thriving of these sectors depend on the dynamics of the rainfall seasons.
Highlights
Rainfall is a major factor that determines crop choice and yield, as well as, success of other socio-economic activities in West Africa
The mean rainfall onset for the forest zone was found to be in the third dekad of March for both gauge and model
Onsets for the forest zone were much earlier than the transition zone and this is possibly due to the gradual migration of the Inter Tropical Discontinuity (ITD) northwards
Summary
Rainfall is a major factor that determines crop choice and yield, as well as, success of other socio-economic activities in West Africa. The variability of rainfall onset, cessation and duration affect planting (sowing) dates, crop growth, yield and food production [1] [2]. Projected rise in population by 2050, is a concern for food stability and natural resource base conservation, and there is the need to investigate the variability of the onset, duration and cessation of the rainfall season over the West African Climate [3]. In Ghana, as in other West African countries, the knowledge on past and present onset, cessation and duration of the rainy season will inform prediction and planning of appropriate interventions towards ensuring yield stability. Amekudzi et al (2015) [2] extensively studied the variability of rainfall onset, cessation and growing season over the country using the rainfall amount and rainy days approach. Omotosho (2002) [11] used the Theta-E technique, which depends on the equivalent potential temperature
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