Variability of the Minor Season Rainfall over Southern Ghana (1981–2018)

Abstract

The monitoring of rainfall variability over recent decades has become a necessity due to its devastating effects such as floods and droughts, which render humans vulnerable across different parts of the West African region. The current study seeks to provide a good understanding of variability within the minor rainfall season over southern Ghana by employing statistical tools to quantify variability in rainfall. Daily rainfall data from 1981 to 2018 for seventeen (17) synoptic weather stations across southern Ghana are used for this analysis. We perform trend and descriptive statistics of rainfall amount and extreme indices intending to identify the areas with the greatest variability in rainfall. Further, for five recent years (2014–2018), we do an interpolation of the ground station rainfall data and compute anomalies. We find increasing trends of rainfall in the minor rainy season for 16 out of the 17 stations, with rainfall increasing between 0.10 mm and 4.30 mm each season. For extreme rainfall indices, the 17 stations show nonsignificant trends of very wet and extremely wet days. We also find that the middle parts of Ghana have the highest rainfall amounts (262.7 mm/season–400.2 mm/season), while the East Coast has the lowest (125.2 mm/season–181.8 mm/season). Over the whole of southern Ghana, we find high variability in rainfall amount with the coefficient of variations (CV) between 25.3% and 70.8% and moderate to high variability in rainfall frequency (CV = 14.0%–48.8%). The results of rainfall anomalies show that the middle parts had an above-normal rainfall amount. In the same period, the transition areas experienced below-normal rainfall. Our finding of high variability in the minor rainfall season has implications for agricultural productivity in Ghana and countries in the West African region, which rely heavily on rain-fed agriculture. Hence, this study recommends more research to understand the causes of variability in the West African monsoon and how this will change in the region.

Agricultural Yield Responses to Climate Variabilities in West Africa: A Food Supply and Demand Analysis

“…According to [65], the variability of the major season is strongly affected by atmospheric moisture that may result in upward humidity trends over the minor period. A recent study by [66] determined a growing rainfall tendency during the minor cycle that agrees with the Mann-Kendall trend results. Also, the greening of the rain forest causes higher surface moisture which most likely enhances the amount of precipitation.…”

Spatial Analysis of Exposure of Roads to Flooding and Its Implications for Mobility in Urban/Peri-Urban Accra

“…In June, the average monthly rainfall is about 175 mm and the highest daily rainfall ever recorded since 2000 was 212.8 mm received on 3 June 2015 [47]. However, there have been growing concerns in the media over the last decade about the increasing occurrence of extreme rainfall events in the minor season (see [48]). This means that floods due to these extreme rainfall events are increasing in frequency and severity in Accra and hence, In June, the average monthly rainfall is about 175 mm and the highest daily rainfall ever recorded since 2000 was 212.8 mm received on 3 June 2015 [47].…”

“…This means that floods due to these extreme rainfall events are increasing in frequency and severity in Accra and hence, In June, the average monthly rainfall is about 175 mm and the highest daily rainfall ever recorded since 2000 was 212.8 mm received on 3 June 2015 [47]. However, there have been growing concerns in the media over the last decade about the increasing occurrence of extreme rainfall events in the minor season (see [48]). This means that floods due to these extreme rainfall events are increasing in frequency and severity in Accra and hence, exacerbating the exposure of infrastructure and human livelihoods to flooding [49] modelled flooding within the Greater Accra Metropolitan Area (GAMA) and identified these neighbourhoods as some of the flood bluespots in Accra.…”

Extreme Temperature and Rainfall Events and Future Climate Change Projections in the Coastal Savannah Agroecological Zone of Ghana

“…Again, Atiah et al [36] found a significant decrease in wet extreme indices over Volta Lake and an increase in wet extreme indices over northern Ghana. In addition, Braimah et al [37] found no significant trends in the number of very wet and extremely wet days in southern Ghana. Variability in temperature and rainfall, as well as an increase in the frequency of extreme weather or climate events, have devastating effects on society, especially in West Africa [38,39] and Ghana, where most of the population relies on rain-fed agriculture [40,41].…”