Variabilities in Rainfall Onset, Cessation and Length of Rainy Season for the Various Agro-Ecological Zones of Ghana

Leonard Amekudzi,Michael Baidu,Samuel Codjoe,Jeffrey Aryee,Edmund Yamba,Kwasi Preko,Ernest Asare

doi:10.3390/cli3020416

Leonard Amekudzi, Michael Baidu + Show 5 more

Open Access

https://doi.org/10.3390/cli3020416

Copy DOI

Abstract

This paper examines the onset and cessation dates of the rainy season over Ghana using rain gauge data from the Ghana Meteorological Agency (GMet) over the period of 1970–2012. The onset and cessation dates were determined from cumulative curves using the number of rainy days and rainfall amount. In addition, the inter-annual variability of the onset and cessation dates for each climatic zone was assessed using wavelet analysis. A clear distinction between the rainfall characteristics and the length of the rainy season in the various climatic zones is discussed. The forest and coastal zones in the south had their rainfall onset from the second and third dekads of March. The onset dates of the transition zone were from the second dekad of March to the third dekad of April. Late onset, which starts from the second dekad of April to the first dekad of May, was associated with the savannah zone. The rainfall cessation dates in the forest zone were in the third dekad of October to the first dekad of November, and the length of the rainy season was within 225–240 days. The cessation dates of the coastal zone were within the second and third dekad of October, and the length of rainy season was within 210–220 days. Furthermore, the transition zone had cessation dates in the second to third dekad of October, and the length of the rainy season was within 170–225 days. Lastly, the savannah zone had cessation dates within the third dekad of September to the first dekad of October, and the length of rainy season was within 140–180 days. The bias in the rainfall onset, cessation and length of the rainy season was less than 10 days across the entire country, and the root mean square error (RMSE) was in the range of 5–25 days. These findings demonstrate that the onset derived from the cumulative rainfall amount and the rainy days are in consistent agreement. The wavelet power spectrum and its significant peaks showed evidence of variability in the rainfall onset and cessation dates across the country. The coastal and forest zones showed 2–8- and 2–4-year band variability in the onsets and cessations, whereas the onset and cessation variability of the transition and savannah zones were within 2–4 and 4–8 years. This result has adverse effects on rain-fed agricultural practices, disease control, water resource management, socio-economic activities and food security in Ghana.

Highlights

The schedule of agricultural activities, right from land preparation, through crop selection and planting, to the time of harvesting for a developing country like Ghana, is rainfall dependent [1,2,3,4]
These results show a clear distinction in the onset from the coastal zone through the forest and transition to the savannah zone, and there are slight differences in some stations for the two methods
The rainfall onset and cessation dates, as well as the length of the rainy season over Ghana have been assessed using rain gauge data from Ghana Meteorological Agency (GMet) covering the period of 1970–2012

Summary

Introduction

The schedule of agricultural activities, right from land preparation, through crop selection and planting, to the time of harvesting for a developing country like Ghana, is rainfall dependent [1,2,3,4]. The assessment and prediction of the onset and cessation dates of the rainy season is crucial to the success of agricultural activities in Ghana [5,6]. The variability in the rainy season onset and cessation could pose socio-economic and developmental challenges as they threaten food security and induce poverty [2,4]. This is so because erratic and significant delays in rainfall affect the country’s overall production of food and, in particular, cereals (maize, millet, soya bean and rice), which form the main staple food in the country. The mosquito population is likely to increase rapidly during the warmer humid conditions [7]

Methods

Results

Conclusion