Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Seasonal Rainfall Variability over Southern Ghana

Version 1 : Received: 5 August 2021 / Approved: 6 August 2021 / Online: 6 August 2021 (08:01:09 CEST)

How to cite: Braimah, M.; Asante, V.A.; Ahiataku, M.; Ansah, S.O.; Otu-Larbi, F.; Yahaya, B.; Ayabila, J.B. Seasonal Rainfall Variability over Southern Ghana. Preprints 2021, 2021080150 (doi: 10.20944/preprints202108.0150.v1). Braimah, M.; Asante, V.A.; Ahiataku, M.; Ansah, S.O.; Otu-Larbi, F.; Yahaya, B.; Ayabila, J.B. Seasonal Rainfall Variability over Southern Ghana. Preprints 2021, 2021080150 (doi: 10.20944/preprints202108.0150.v1).

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.

Keywords

rainfall trend; Mann Kendall’s test; Sen’s slope estimator; climate statistics; seasonal rainfall; standardized anomaly index; extreme precipitation indicators; rainfall variability; southern Ghana

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