Trends in Spatio-Temporal Rainfall Variability in Ghana, (1951-2000)

Abstract

Rainfall variability in humid West Africa (south of 8oN) is less studied than that of the Sahelian zone, the data for which are responsible for the general consensus of a downward rainfall trend in West Africa over the last few decades. Such a generalization may not be useful for modelling and planning purposes. Rainfall mechanisms in the drier Sahel and the humid Guinea Coast region differ; the former region has a single rainfall peak (in summer) but the latter region has a bi-modal seasonal distribution. It is therefore not necessarily true that a failure in the rainfall regime in one zone – and its subsequent impact on agriculture and livelihood – means the same for the other. In fact, it has been observed that a warmer South Atlantic is associated with more rainfall in the Guinea Coast region and less rainfall in the Sahel (Gu and Adler, 2003). It is also suggested that the El Niño-Southern Oscillation phenomenon (ENSO) may be more strongly associated with Sahelian rainfall than with that of the Guinea Coast region (Ward et al., 2004). Therefore there is a need to investigate rainfall trends and variability in the humid areas to better inform agricultural decision-makers. Agricultural productivity has decreased in recent decades following declining rainfall since the early 1970s, with the rainfall showing signs of improvement after 2000. This analysis will contribute to the knowledge of rainfall trends and aid in agricultural and allied industrial decision-making in this important agro-climatic zone. The study utilizes annual rainfall totals over 50 years to identify the spatial and temporal dimensions of rainfall variability in Ghana by comparing the characteristics of the period 1951 to 1970 and 1981 to 2000, hereafter referred to as P1 and P2 respectively. Specific emphasis is placed on the subhumid area of mid-Ghana because of its national and regional significance to agricultural production and food security.