Browsing by Author "Aryee, Jeffrey"

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    Development of high spatial resolution rainfall climatology for Ghana
    (July 2015) Aryee, Jeffrey
    Various sectors of the country’s economy (health, energy, agriculture, planning and many others) depend on climate, and as such availability of quality climate data becomes essential for climate impact studies in these sectors. In this study, rainfall climatology database has been developed for Ghana using GMet station datasets distributed over the four agro-ecological zones and spanning a 33-year period (1980 – 2012). Datagaps within the rainfall time-series were filled by Regularized Expectation Maximization (RegEM) and homogenization of the time-series was performed by Quantile Matching Adjustments (QMadj). The homogenized datasets were then gridded at a high-spatial resolution (0:25 o x 0:25 o ) using Minimum Surface Curvature (MSC) with tensioning parameter. Seasonal rainfall for the four agro-ecological zones have been derived based on the grids covering the entire country and this allowed a clear evidence of the migration of Inter-Tropical Discontinuity (ITD) from the South of the country to the North and back; thus, establishing a uni-modal rainfall regime over the Northern part of the country and a bi-modal rainfall regime over the Southern part of the country. Finally, Climatic Research Unit Time-Series 3.22 (CRU TS 3.22) monthly precipitation data was used to validate the gridded dataset, obtaining high Pearson’s correlation co-efficients (0.5 – 0.9), low relative mean difference (0 – 0.3) and low relative root mean square error values (0 – 8). At present, a country-wide rainfall climatology has iii been developed from GMet rainfall time-series which will serve as a precursor for further climate impact study, in the aforementioned sectors, across the country.
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    Variabilities in Rainfall Onset, Cessation and Length of Rainy Season for the Various Agro-Ecological Zones of Ghana
    (Climate, 2015-06-15) Amekudzi, Leonard K.; Yamba, Edmund I.; Preko, Kwasi; Asare, Ernest O.; Aryee, Jeffrey; Baidu, Michael; Codjoe, Samuel N. A.
    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.