Seasonal Rainfall Variability over Southern Ghana

Abstract

Rainfall variability has resulted in extreme events like devastating floods and droughts which is the main cause of human vulnerability to precipitation in West Africa. Attempts have been made by previous studies to understand rainfall variability over Ghana but these have mostly focused on the major rainy season of April-July, leaving a gap in our understanding of the variability in the September-November season which is a very important aspect of the Ghanaian climate system. The current study seeks to close this knowledge gap by employing statistical tools to quantify variabilities in rainfall amounts, rain days, and extreme precipitation indices in the minor rainfall season over Ghana. We find extremely high variability in rainfall with a Coefficient of variation (CV) between 25.3% and 70.8%, and moderate to high variability in rain days (CV=14.0% - 48.8%). Rainfall amount was found to be higher over the middle sector (262.7 mm – 400.2 mm) but lowest over the east coast (125.2 mm – 181.8 mm). Analysis of the second rainfall season using the Mankandell Test presents a non-significant trend of rainfall amount and extreme indices (R10, R20, R99p, and R99p) for many places in southern Ghana. Rainfall Anomaly Indices show that the middle sector recorded above normal precipitation which is the opposite for areas in the transition zone. The result of this work provides a good understanding of rainfall in the minor rainfall season and may be used for planning purposes.

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

“…Special thanks go to the Ghana Meteorological Agency for providing the data that was used in this work. preprints.org [65] is appreciated for allowing us to deposit the paper on their server.…”

Long-Term Evolution of Rainfall and Its Consequences on Water Resources: Application to the Watershed of the Kara River (Northern Togo)

“…The Mann-Kendall tendency test is a simple and robust test that accepts missing data but hardly detects annual trends [14]. This test was used in other studies to evaluate the importance of a trend within chronological series of climatic data [20,22,[24][25][26][27][58][59][60]. A positive value for the Mann-Kendall slope expresses an upward trend and a negative value implies a downward trend.…”

“…During the last years, numerous research studies have used parametric and nonparametric tests to define tendencies within chronological series [22][23][24][25][26][27][28][29][30][31] The most commonly used are the Mann-Kendall [32,33] and Sen [34] tests. More recently, Sen [35] developed a new methodological approach, the innovative trend analysis (ITA), to detect tendencies in chronological data series.…”