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Large parts of southern Africa are influenced by extra-tropical weather systems for most of the year. During late summer (December–March), the circulation over the area becomes distinctly tropical. This paper introduces the Africáne, a synoptic scale tropical low-pressure system which has been shown to cause widespread and heavy rainfall over the southern sub-continent of Africa. The frequency of occurrence of Africánes, their contribution to rainfall and interannual variability are discussed in this paper. Africánes occur most frequently at the longitude of the Caprivi area with a second peak in frequency at around 32.5° E. They mostly occur over Namibia, Botswana and Zimbabwe and only infrequently infiltrate as far south as the borders of South Africa. However, when they do occur over South Africa, they cause widespread heavy rainfall and floods. Rainfall is mostly confined to the eastern flank of Africánes and between 20 and 35% of the annual rainfall over southern Africa in late summer can be attributed to these systems. There are two main synoptic regimes associated with Africánes: a westerly wave or tropical-temperature trough combines with the Africáne to pull rainfall southwards into South Africa. The second, is a mid-level subtropical high pressure, located south of the Africáne, which causes the rainfall to be confined to the north. The interannual variability of Africánes are closely linked to rainfall over southern Africa, such that an above normal number of Africánes in a season causes above normal rainfall over southern Africa. The number of Africánes that form per year is linked to El Niño–Southern Oscillation (ENSO). It is recommended that the predictability of Africánes on different time scales should be investigated. [ABSTRACT FROM AUTHOR]

The positive phase of the subtropical Indian Ocean dipole (SIOD) is one of the climatic modes in the subtropical southern Indian Ocean that influences the austral summer inter-annual rainfall variability in parts of southern Africa. This paper examines austral summer rain-bearing circulation types (CTs) in Africa south of the equator that are related to the positive SIOD and the dynamics through which specific rainfall regions in southern Africa can be influenced by this relationship. Four austral summer rain-bearing CTs were obtained. Among the four CTs, the CT that featured (i) enhanced cyclonic activity in the southwest Indian Ocean; (ii) positive widespread rainfall anomaly in the southwest Indian Ocean; and (iii) low-level convergence of moisture fluxes from the tropical South Atlantic Ocean, tropical Indian Ocean, and the southwest Indian Ocean, over the south-central landmass of Africa, was found to be related to the positive SIOD climatic mode. The relationship also implies that positive SIOD can be expected to increase the amplitude and frequency of occurrence of the aforementioned CT. The linkage between the CT related to the positive SIOD and austral summer homogeneous regions of rainfall anomalies in Africa south of the equator showed that it is the principal CT that is related to the inter-annual rainfall variability of the south-central regions of Africa, where the SIOD is already known to significantly influence its rainfall variability. Hence, through the large-scale patterns of atmospheric circulation associated with the CT, the SIOD can influence the spatial distribution and intensity of rainfall over the preferred landmass through enhanced moisture convergence. [ABSTRACT FROM AUTHOR]

In this paper, daily characteristics of the Central Africa rainfall are assessed using the regional model REMO in the framework of contributions to the CORDEX-Africa project. The model is used to dynamically downscale two global climate models (MPI-ESM-LR and EC-EARTH) for the present (1981–2005) and future (2041–2065, 2071–2095) climate under the Representative Concentration Pathway (RCP) 2.6, 4.5, and 8.5 emission scenarios. A substantial spatio-temporal variability of the daily precipitation characteristics is obtained, as well as varying inferences for individual indices. For the present days, both REMO's runs capture reasonably well the mean seasonal rainfall, the frequency of wet days, the threshold of extreme rainfall, and the cumulative frequency of daily rainfall. The model better simulates the frequency of rainy days than their intensity. It is found that origins of model biases differ as a function of regions. Over the continent, boundary conditions tend to influence the spatial distribution of rainfall whereas over oceanic and coastal regions, REMO's physics seems to dominate over the boundary forcing. The projected frequency of wet days shows a decrease along the twenty-first century over most part of the continent. Throughout the century, all scenarios of REMO decrease the rate of rainfall with increasing intensity, and which will be noticeable in the Sahelian region at late twenty-first century. Furthermore, the extreme event thresholds decrease over Sahelian regions and increase along the coastal regions. [ABSTRACT FROM AUTHOR]

Given its high dependence on rainfed agriculture and its comparatively low adaptive capacity, Africa is frequently invoked as especially vulnerable to climate change. Within Africa, there is likely to be considerable variation in vulnerability to climate change both between and within countries. This paper seeks to advance the agenda of identifying the hot spots of what we term 'climate security' vulnerability, areas where the confluence of vulnerabilities could put large numbers of people at risk of death from climate-related hazards. This article blends the expertise of social scientists and climate scientists. It builds on a model of composite vulnerability that incorporates four 'baskets' or processes that are thought to contribute to vulnerability including: (1) physical exposure, (2) population density, (3) household and community resilience, and (4) governance and political violence. Whereas previous iterations of the model relied on historical physical exposure data of natural hazards, this paper uses results from regional model simulations of African climate in the late 20th century and mid-21st century to develop measures of extreme weather events-dry days, heat wave events, and heavy rainfall days-coupled with an indicator of low-lying coastal elevation. For the late 20th century, this mapping process reveals the most vulnerable areas are concentrated in Chad, the Democratic Republic of the Congo, Niger, Somalia, Sudan, and South Sudan, with pockets in Burkina Faso, Ethiopia, Guinea, Mauritania, and Sierra Leone. The mid 21st century projection shows more extensive vulnerability throughout the Sahel, including Burkina Faso, Chad, Mali, northern Nigeria, Niger, and across Sudan. [ABSTRACT FROM AUTHOR]

This paper presents the first interdecadal and interannual periodisation of the climate in West Africa between 1750 and 1800. The climatic synthesis is founded on previously unexploited British documents written at Cape Coast Castle, Cape Coast, Ghana and travel journals, which are combined with previous research on the Sahel. By combining historical evidence with the most recently identified rainfall patterns in the Sahel and the Guinea coast, the climatic periodisation distinguishes between wetter and drier periods. The results show that there was great interannual and interdecadal variability in the West African rainfall regime in the 18th century. The historical evidence suggests that the climate in the Sahel and the Guinea coastal interior alternated between five wet and dry periods, whereas the coastal dry zone alternated between three wet and dry periods. The most pronounced changes in the climate are found in the 1780s and 1790s. The Guinea coastal interior and the Sahel experienced a wet period in the 1780s and a dry period in the 1790s, whereas the coastal dry zone was drier in the 1780s and wetter in the 1790s. The investigation shows that the secondary rainy season on the Gold coast was weak or non-existent. [ABSTRACT FROM AUTHOR]

This paper examines the connection between the probability of precipitation and forecast amounts from Weather Research and Forecasting (WRF) model runs over Central and West Africa. A one season period (June-September 2010) was used to investigate the quantitative precipitation forecast-probability relationship. The predictive capability of this relationship was then tested on an independent sample of data (June-September 2011); 2010 and 2011 were wet and dry years, respectively. The results show that rainfall is less likely to occur in those areas where the model indicates no precipitation than it is elsewhere in the domain. Rainfall is more likely to occur in those regions where precipitation is predicted, especially where the predicted precipitation amounts are largest. The probabilities of rainfall forecasts based on this relationship are found to possess skill as measured by relative operating characteristic curves, reliability diagrams, and Brier skill scores. Skillful forecasts from the technique exist throughout 24-h periods for which WRF output was available. The results suggest that this forecasting tool might assist forecasters throughout the season in a wide variety of weather events and not only in areas of difficult-to-forecast convective systems. [ABSTRACT FROM AUTHOR]

This paper is devoted to the first results from the GHYRAF (Gravity and Hydrology in Africa) experiment conducted since 2008 in West Africa and is aimed at investigating the changes in water storage in different regions sampling a strong rainfall gradient from the Sahara to the monsoon zone. The analysis of GPS vertical displacement in Niamey (Niger) and Djougou (Benin) shows that there is a clear annual signature of the hydrological load in agreement with global hydrology models like GLDAS. The comparison of GRACE solutions in West Africa, and more specifically in the Niger and Lake Chad basins, reveals a good agreement for the large scale annual water storage changes between global hydrology models and space gravity observations. Ground gravity observations done with an FG5 absolute gravimeter also show signals which can be well related to measured changes in soil and ground water. We present the first results for two sites in the Sahelian band (Wankama and Diffa in Niger) and one (Djougou in Benin) in the Sudanian monsoon region related to the recharge-discharge processes due to the monsoonal event in summer 2008 and the following dry season. It is confirmed that ground gravimetry is a useful tool to constrain local water storage changes when associated to hydrological and subsurface geophysical in situ measurements. [ABSTRACT FROM AUTHOR]