Browsing by Author "Baidu, Michael"

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    Assessment of Long-term Spatio-temporal Rainfall Variability over Ghana usingWavelet Analysis
    (May 2016) Baidu, Michael
    Rainfall variability has serious implications on food security and livelihood in West Africa since it modulates the socio-economic activities in the sub region. The interannual, inter-seasonal and inter-decadal rainfall variability in rainfall over Ghana has been studied and their periodicities analysed using wavelet analysis. A rainfall time series from 1901 - 2010 from GPCC was used in this analysis. It was observed that, high cumulative rainfall amounts ranging from 900 - 1900 mm are recorded over the entire nation per year with very high rainfall amounts between 1500 - 1900 mm recorded at the south-western part of the country and low rainfall amounts (900 - 1200 mm) recorded in the Savannah and east coast of the country. In general a decreasing trend is observed for the inter-annual rainfall over all the agro-ecological zones except for the coastal zone where a slight rise in trend of 0.1600 mm per year is seen. The seasonal trend analysis reveals a significant decreasing trend at 99% confidence level in all the agro-ecological zones except for the Savannah during the DJF season indicating an intensification of the Harmattan. The Coastal zone records lowest mean rainfall values for all the seasons with the highest of about 150 mm recorded in MAM. The Forest zone on the other hand records very high rainfall values for all the seasons with the highest of about 200 mm recorded in JJA followed by about 170 mm in MAM. The Transition zone however records almost similar rainfall values (varying between 120 and 170 mm) for all the seasons except for DJF where a lower mean value of about 50 mm is recorded. On inter-decadal time scale, below normal rainfall values is observed between the 1901 - 1920 and 1980 - 2010 periods for all the agro-ecological zones except for the Savannah which shows above normal rainfall values within the 1901 - 1940 period. These variabilities confirm the effects of strong El Niño and La Niña episodes on the region. The wavelet analysis also revealed a strong annual periodicity over all the agro-ecological zones except for the Coastal and Forest zones where the annual periodicity is accompanied by 4 - 8 months signal. The results of both the 5 year moving average and the inter-decadal anomaly confirm that rainfall amount is significantly decreasing even in the transition zone which is the food hub of the country. This will likely have negative consequences on agricultural practices, water resource management and food security.
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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.