Influence of Climate Change on the Future Precipitation Pattern in the Region of Ghana

2019

English

Model predictions for the Ghana region are highly uncertain and in most cases do not show any significant trend within the 95% confidence interval. Over western West Africa, the monsoon system and rainfall started to strengthen from 1998 indicating a new inter-decadal variation. Ghana displayed a negative annual trend of precipitation ranging from -50 to -100 mm/year for the period 1951-2010. By the end of the 21st century a small delay in the monsoon season and an intensification of lateseason precipitation events are projected across West Africa. The implications for future changes in Ghanaian mean rainfall are uncertain primary due to the inability of global climate models to resolve convective rainfall and due to the lack of available historical data. In Accra city and in the broader area of Ghana, seasonal rainfall averages are anticipated to increase (0.2 mm day−1) with a 1.5°C of global warming under the RCP 8.5 high GHG-forcing scenario. Projections for consecutive wet days (CWT) show a reverse pattern with CWT being reduced by one day or two days. According to the RCP 4.5 mid-level and to the RCP 2.6 low-level GHG scenarios a small increase in precipitation is projected during the rainy season (i.e. 0.1-0.2 mm day−1 precipitation changes per changes of global annual mean surface-air temperature in oC) and a small decrease of precipitation during the dry season (0-0.1 mm day−1 oC−1) across Ghana. For the same area, under the SRES A1b scenario it is also projected a small increase of annual precipitation (0-0.1 mm day−1 oC−1). Under RCPs 4.5 and 8.5 scenarios, recent studies projected an increase in the frequency and intensity of extreme rainfall events over West Africa. Based on physical reasoning it could be suggested that projected increases in heavy precipitation and sea level extremes would contribute to increases in local flooding, although there is low confidence in projections of changes in fluvial floods because the causes of regional changes (e.g., soil moisture gradients and topographic particularities) are complex. Under the A1F1 scenario sea level may rise up to 0.79 m along the coastline of Accra leading to a shoreline recession of 200 m by the year 2100. The southwestern part Volta basin and Oti basin in Ghana will probably experience increases in runoff by 2050 under the SRES A1b scenario. The fluctuations in runoffs, particularly in the Volta River, may increase the risk of floods and/or droughts.

Trepekli, K.; Friborg, T.; Allotey, A. N. M.; Møller-Jensen, L.