Atmospheric response to SST tendancy in the Eastern topical Atlantic in July-August

<p><span>The objective of this work is to understand how the seasonal tend</span><span>ance</span><span>s of the tropical Atlantic SST influence the migration of the Intertropical Convergence Zone (ITCZ) and the West African precipitation associated with it. For this we carried out different sensitivity tests to the SST, climatological, with the regional atmospheric model WRF-ARW. Our results, based on the July-August period, show a strong influence of SST anomalies in the Dakar Nino (DN) and </span><span>Atlantic </span><span>cold tongue (</span><span>ACT</span><span>) regions on the marine ITCZ and West African precipitation. Above the ocean, the cooling of the tropical northeast Atlantic induces a strong reduction in precipitation north of 10°N, associated with the southward displacement of the ITCZ which is located between 5°-10°</span><span>N </span><span>with a slight increase in rains. On the other hand, the warming of the SST of the tropical south-eastern Atlantic induces an increase in marine precipitation</span><span>s</span><span>, with a maximum centered on 5°N, explained by the location of the ITCZ </span><span>f</span><span>urther south than that associated with the cooling in the region of DN. On the continent, the influence of these SST tend</span><span>ance</span><span>s is characterized by the presence of a zonal dipole of rainfall anomalies over the Sahelian regions. The SST cooling effect in the DN region is more marked in the western Sahel, particularly in Senegal, with a sharp drop in rainfall in this region. While that of warming in the LEF region is more marked in the Sahel, which also induces a strong reduction in the intensity of the rains in this region. However, the combined experience of these two type anomalies shows a dipole of rainfall anomalies over the ocean and over the continent. This dipole is characterized by a decrease (increase) in Sahelian (Guinean) rainfall. Our results also show that, for all simulations, the increase (reduction) in precipitation is more explained by the convective (non-convective) part of the rain. The influence of the SST of DN contributes 40% to 100% on the decrease in rainfall in the West Sahel, while the SST of the </span><span>ACT</span><span> reduces rainfall in the eastern Sahel by 40% to 100%. Thus, this work underlines the importance of taking into account the effect of the seasonal anomaly of the SST of DN on Sahelian precipitation</span><span>s</span><span> in forecasting models.</span></p>

Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves

Heatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.

LANDMARK EMPIRES: SEARCHING FOR MEDIEVAL EMPIRES AND IMPERIAL TRADITION IN HISTORIOGRAPHIES OF WEST AFRICA

The history of medieval West Africa is defined by the age of three great empires that succeeded one another: Ghāna, Māli, and Songhay. How did these empires come to frame our view of the West African past? To answer the question, we have to understand first how the European and Eurocentric concept of an empire was imposed on a specific African context and why it thrived. In this respect, the case of Sudanic empires in particular illuminates the process of history writing and scholars’ relationship with their time and object of study. In the last few years, Sudanic empires have made a prominent return to the historical conversation. I propose here a critical reflection on ‘empire’ and ‘imperial tradition’ in the western Sahel based on europhone and non-europhone (Arabic) historiographies, from the first histories written in postmedieval West Africa to those produced by twenty-first-century scholarship.

Women in Mali

Over centuries, a variety of decentralized societies and centralized states have formed in territories across the western Sahel and southwest Sahara, and along the Niger and Senegal river valleys. Women have played central yet often unacknowledged roles in building these communities. By the late 11th century, some were rulers, as tombstones from the Gao region seem to suggest. A travelogue describing the Mali empire, and a chronicle from Songhay, tell stories of women who plotted political dissent or staged rebellions in the 14th–16th centuries. By and large, everyday women’s reproductive and productive labor sustained their families, and structured life in agricultural, pastoral, fishing, or trading communities. In the 1700s in Segu, women brewed mead, cultivated crops, dyed textiles, and participated in the building of fortifications. In Masina in the 1800s, girls attended qurʾanic school, and a woman was the custodian of the caliph’s library. Women also suffered great violence stemming from conflicts, forced displacement, and slavery. By the end of the 19th century, they made up a considerable portion (at times the majority) of enslaved individuals in the region. After the European conquest and creation of the French Soudan colony, the French administration imposed an export-oriented wage economy, in which women worked to supply crops and sustain infrastructure projects. From the regions of Kayes, Kita, and Nioro, many migrated to groundnut- or gold-producing regions of Senegambia. While women’s labor and migrations were seldom accounted for in administrative records, their attempts to leave unhappy marriages or escape enslavement do appear in court records. However, colonial domination was gendered: the administration ultimately shunned women’s emancipation efforts, seeking to channel its rule by reinforcing patriarchal authority in communities. In 1960, the Republic of Mali achieved independence. Under the democratic and military governments that followed, women built pan-African and transnational alliances. In 1991 and beyond, they fought to achieve more rights, and greater political power and representation. Their labor and migrations have continued to sustain a large portion of the economy. Post-2011, they have been both active participants in, and victims of, the conflicts that have engulfed the country, suffering displacement, loss of livelihood, and sexual violence, for which many have yet to receive justice.

Spatial Variation and Trend of Extreme Precipitation in West Africa and Teleconnections with Remote Indices

Extreme precipitation is a great concern for West Africa country, as it has serious consequence on key socio-economic activities. We use high resolution data from the Climate Hazards Group InfraRed Precipitation Stations (CHIRPS) to determine the spatial variability, trend of 8 extreme precipitation indices in West Africa and their relationship to remote indices. Spatial variability of extreme is characterized by maximum precipitation over the orographic regions, and in southern Sahel. The trend analysis shows a decrease of dry condition in Sahel and Sahara, and an increase tendency of wet indices over western Sahel and southern Sahel. The correlation analysis reveals that extreme precipitation in Sahel is strongly teleconnected to the Eastern Mediterranean Sea (EMS), whereas western and western-north Sahel is associated with both Atlantic Meridional Mode (AMM), Maiden Julian Oscillation phase 8 (MJO8), El Niño 3.4 index (NINO.3.4), and Trans-Atlantic-Pacific Ocean Dipole Index (TAPODI) but with different characteristics or directions. Guinean coast extreme precipitation is highly associated with Atlantic zone 3 SST anomaly (ATL3), Northern Cold Tongue Index (NCTI), TAPODI but also with an opposite sign with NINO.3.4 and in somewhat with the MJO8.

Future evolution of the Sahel precipitation zonal contrast in CESM1

The main focus of this study is the zonal contrast of the Sahel precipitation shown in the CMIP5 climate projections: precipitation decreases over the western Sahel (i.e., Senegal and western Mali) and increases over the central Sahel (i.e., eastern Mali, Burkina Faso and Niger). This zonal contrast in future precipitation change is a robust model response to climate change but suffers from a lack of an explanation. To this aim, we study the impact of current and future climate change on Sahel precipitation by using the Large Ensemble of the Community Earth System Model version 1 (CESM1). In CESM1, global warming leads to a strengthening of the zonal contrast, as shown by the difference between the 2060–2099 period (under a high emission scenario) and the 1960–1999 period (under the historical forcing). The zonal contrast is associated with dynamic shifts in the atmospheric circulation. We show that, in absence of a forced response, that is, when only accounting for internal climate variability, the zonal contrast is associated with the Pacific and the tropical Atlantic oceans variability. However, future patterns in sea surface temperature (SST) anomalies are not necessary to explaining the projected strengthening of the zonal contrast. The mechanisms underlying the simulated changes are elucidated by analysing a set of CMIP5 idealised simulations. We show the increase in precipitation over the central Sahel to be mostly associated with the surface warming over northern Africa, which favour the displacement of the monsoon cell northwards. Over the western Sahel, the decrease in Sahel precipitation is associated with a southward shift of the monsoon circulation, and is mostly due to the warming of the SST. These two mechanisms allow explaining the zonal contrast in precipitation change.

Using the CHIRPS Dataset to Investigate Historical Changes in Precipitation Extremes in West Africa

This study aims to provide improved knowledge and evidence on current (1986–2015) climate variation based on six rainfall indices over five West African countries (Senegal, Niger, Burkina Faso, Ivory Coast, and Benin) using the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) dataset. On average, precipitation has increased over the central Sahel and the western Sahel. This increase is associated with increase in the number of rainy days, longer wet spells and shorter dry spells. Over the Guinea Coast, the slight increase in precipitation is associated with an increase in the intensity of rainfall with a shorter duration of wet spells. However, these mean changes in precipitation are not all statistically significant and uniform within a country. While previous studies are focused on regional and sub-regional scales, this study contributes to deliver a climate information at a country level that is more relevant for decision making and for policy makers, and to document climate-related risks within a country to feed impact studies in key sectors of the development, such as agriculture and water resources.

Reading with the colonial in the life of Shaykh Musa Kamara, a Muslim scholar-saint

The colonial-era Senegalese Muslim intellectual Shaykh Musa Kamara is best known for his over 1,700-page Arabic-language text about the history and social organization of the greater Western Sahel, Zuhūr al-basātīn fī tārīkh al-Sawādīn (Flowers in the Gardens in the History of the Blacks). Long celebrated by nationalist historiography as proof of an autochthonous historical consciousness and a spirit of tolerance, his status as a point of reference has been renewed in the contemporary context of Islamist political violence in the region. However, these receptions do not account for Kamara's own intellectual project, nor do they exhaust the possible readings of him in the present. In addition to thinking about Senegal in terms that cohere with the modern, Kamara also offers a way of thinking about the Muslim-majority West African country, and the greater Western Sahel more generally, in terms that have emerged from the historical specificity of the region. These include saintly subjectivity, notions of power irreducible to either the religious or the political, and a method of genealogical criticism. Importantly, he developed these ideas at the moment when a consensus about the place of Islam in colonial governance was being elaborated. Revisiting his body of work permits us to consider an analytical language about an African society with deep histories of Islam and an intellectual elaboration that was expressed within and sought to intervene in a colonial context.