Investigating the dynamics and drivers of extreme rainfall in Ghana

Abstract

Daily rainfall data from Ghana Meteorological Agency (GMet) rain gauge network was analysed to identify extreme rainfall events in Ghana. The data was first processed in order to remove all errors in the observational time series prior to analysis. The data was then analysed by excluding all rainfall events, which fell below a pre-determined threshold in order to identify extreme rainfall event days and non-extreme event days. Inter-annual variability and trends of annual precipitation totals in Ghana are analyzed considering different gridded observational and ERA-Interim re-analysis products. The spatial and temporal distribution of the different rainfall seasons (wet and dry) over Ghana was analyzed in the period 1988-2014. The total annual precipitation as well as extreme precipitation showed a general shift towards a wet climate in the study area. Most of the variables analysed, specific humidity and horizontal moisture flux during extreme and non extreme events showed significant differences. These are the key variables when describing climatological differences between extremes and non extremes. The surface specific humidity distribution has relatively higher values during extreme events than the non-extreme events. The transport of moisture flux along the boundary layer at 850 hPa shows a more westward transport in wet seasons. The extreme events are favoured by southwesterly wind flow and stronger northeasterly winds as compared with the non-extreme events.