Droughts pose a major risk in most African countries including Ghana where agricultural activities are heavily dependent on rainfall. Efforts at assessing droughts and providing decision support tools to farmers are hampered by a lack of rainfall and other meteorological data over many parts of Africa. Satellite based rainfall measurements have been suggested to fill the rainfall data gaps over Africa to enable effective assessment of droughts. Traditional methods of assessing droughts have been based on statistical formulations that relied mostly on precipitation. This approach to assessing droughts ignores important soil water balance processes such as evapotranspiration and antecedent soil moisture which limits its applicability to agricultural drought assessment. We use in-situ observation data (OBS), satellite estimated rainfall data (TAMSAT) and the Joint UK Land and Environment Simulator model to study soil moisture and how it impacts on crop production. The response of soil moisture to changes in vegetation and soil type is tested through a series of experiments in which the soil and vegetation parameters in JULES are changed. TAMSAT was found to persistently underestimate the intensity and amount of rainfall and as a result soil moisture content over northern Ghana but showed good skill replicating the inter-annual variations and the occurrence of rainfall during the rainy season. Soils with greater clay contents showed more tendencies to have drought than those with lesser clay content. Land surfaces with C3 grass were found to be less prone to droughts than those with C4 grass. Meteorological wet and dry years were found not to correspond to agricultural wet and dry years highlighting the importance of using soil moisture for assessment agricultural drought as was done in this study.
Notes: A dissertation submitted in partial fulfilment of the requirement for the degree of Master of Science in Applied Meteorology and Climate with Management. - If you wish to download the full text, please contact library(at)wmo.int (Please replace (at) by @).
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