Precipitation variability and trends in Ghana: An intercomparison of observational and reanalysis products

Abstract

Inter-annual variability and trends of annual/seasonal precipitation totals in Ghana are analyzed considering different gridded observational (gaugeand/or satellite-based) and reanalysis products. A qualitycontrolled dataset formed by fourteen gauges from the Ghana Meteorological Agency (GMet) is used as reference for the period 1961-2010. Firstly, a good agreement is found between GMet and all the observational products in terms of variability, with better results for the gauge-based products-correlations in the range of 0.7-1.0 and nearly null biases-than for the satellitegauge merged and satellite-derived products. In contrast, reanalyses exhibit a very poor performance, with correlations below 0.4 and large biases in most of the cases. Secondly, a Mann-Kendall trend analysis is carried out. In most cases, GMet data reveal the existence of predominant decreasing (increasing) trends for the first (second) half of the period of study, 1961-1985 (1986-2010). Again, observational products are shown to reproduce well the observed trends-with worst results for purely satellite-derived data-whereas reanalyses lead in general to unrealistic stronger than observed trends, with contradictory results (opposite

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