Rainfall variabilities and droughts in the Savannah zone of Ghana from 1960-2015

Abstract

In the Savannah region of Ghana, water scarcity appears to be a frequent occurrence, which is expected to worsen with the anticipated reductions in the quantity of rainfall received. A better estimation of future occurrences and the subsequent preparations are hinged on a solid understanding of past climatic patterns. Given that, trends in rainfall were analysed using the non-parametric Mann-Kendal test for nine (9) climate stations in as well as the entire Savannah zone of Ghana. from 1960 to 2015. No significant trends were observed in annual rainfall for the entire study area as well as individual climate stations except Wenchi, where a negative trend (Sen's slope = -3.30, p-value = 0.01) was recorded at a 0.05 level of significance The Standardised Precipitation Index (SPI) was used to study rainfall anomalies. Droughts were observed to be a regular feature of the climate, occurring at alternating intervals with wet periods. Recovery of the wet periods from the droughts was observed to be declining post the year 2000. For most locations, 1983 recorded the most intense drought while a few others like Navrongo and Wa also saw 2015 being hardly hit by another. Aridity in the study area was found to be intensifying, with aridity index values increasing at a rate of 0.2/decade, although this was not found to be significant (p-value = 0.06) at a 0.05 level of significance. Similar to rainfall, aridity for most of the stations appeared to be increasing although these changes were not statistically significant except for Wenchi, which again recorded a significant increase (p-value of 0.02).