Long-term spatio-temporal variability and change in rainfall over Ghana (1960–2015)

Abstract

Assessment of the change in the characteristics of precipitation for more than half a century (1960–2015) is important for determining the extent of climate change on the country Ghana, and more specifically, the Northern Savannah Agro-ecological Zone (NSAZ). This is because the change in the attributes of rainfall has a direct impact on the quality of livelihood and is crucial not only for the sustenance of natural systems but also for agriculture productivity and the supply of food. The analysis involved the determination of the Daily Precipitation Analysis (Annual Total precipitation, Number of wet days, Number of dry days, Number of wet spells, and Number of dry spells) for the period and trend analysis using Mann-Kendall test and Sen's slope estimation. The following climate extreme indices; R10mm, R20mm, R25mm, CDD, CWD, PRCPTOT, SDII were also computed to assess the level of change in rainfall characteristics for the country. It is observed that Inter-annual, decadal changes and the general trend in Total precipitation (PRCPTOT) show a decline which is higher for the country than for the NSAZ. On the other hand, NSAZ has a higher variability observed in terms of the standard deviation and the coefficient of Variation (CoefVar). There is a general drying up of the climate evident in the decline in rainfall amount (PRCPTOT) and intensity (SDII), and this pattern exhibits a latitudinal decrease from the south (5°N) to the north (11°N). We observe the decrease in PRCPT from latitude 4°N up to latitude 10°N with some exceptional years of increases, however, from latitude 10.3°N up to 11°N, there is a steep increase in the driest part of the country especially to the north east. SDII is the only precipitation indices which have a positive and significant relationship with the AMO for both national and Zone. All other indices have Negative and insignificant values of the relationship AMO. NAO has a negative correlation with all the Precipitation indices except CDD and Dry days. This indicates that as NAO increases, PRCPTOT, Wet days, CWD, R10mm, R20mm, R25mm, and SDII decreases, or vice versa.