Modern drought conditions in western Sahel unprecedented in the past 1600 years

Abstract

As climate model uncertainties remain very large for future rainfall in the Sahel, a multicentennial perspective is required to assess the situation of current Sahel climate in the context of global warming. We present here the first record of hydroclimatic variability over the past 1600 years in Senegal, obtained from stable oxygen isotope analyses (δ 18 O) in archaeological shell middens from the Saloum Delta. During the preindustrial period, the region was relatively humid, with maximum humidity reached during the period from AD 1500 to AD 1800, referred to as the Little Ice Age. A significant negative link is observed at the centennial scale between global temperature and humidity in the Sahel that is at odds with the expected effects of latitudinal shifts of the intertropical convergence zone during the last millennium. In the context of the past 1600 years, the Western Sahel appears to be experiencing today unprecedented drought conditions. The rapid aridification that started ca. AD 1800 and the recent emergence of Sahel drought from the natural variability point to an anthropogenic forcing of Sahel drying trend. This new long-term perspective suggests that the recovery of Sahel rainfall in the last decade may only result from short-term internal variability, and supports climate models that predict an increase of Sahel drought under future greenhouse climate.

The impact of climate change on incomes and convergence in Africa

“…Even though some of the climatic conditions currently experienced on the African continent are unprecedented (e.g. the drought conditions in the Sahel - Carré et al, 2018), limiting global warming below 1.5°C by the end of the century would reduce the occurrence of climate-related extremes such as heat waves compared to a scenario in which global mean temperature reaches 2.0°C by 2100 (Nangombe et al, 2018). Lessening the occurrence of such extremes could have significant benefits in avoiding social and economic impacts (Nangombe et al, 2018).…”

The Iso2k database: a global compilation of paleo-<i>δ</i><sup>18</sup>O and <i>δ</i><sup>2</sup>H records to aid understanding of Common Era climate

“…In some ocean settings, the close coupling between ocean and atmosphere variability leads to co-occurring cool and dry (or warm and wet) anomalies that produce complementary isotopic anomalies (Carilli et al, 2014;Russon et al, 2013;Stevenson et al, 2015Stevenson et al, , 2018) (e.g., ENSO variability; Cobb et al, 2003). In estuarine or freshwater settings, mollusk δ 18 O values are closely linked to the local precipitation-evaporation budget (Azzoug et al, 2012;Carré et al, 2019). Coral δ 18 O and δ 13 C contain a vital effect and coral δ 18 O is offset from δ 18 O w , whereas mollusk and sclerosponge δ 18 O is generally precipitated in equilibrium with environmental water.…”

A predominantly tropical influence on late Holocene hydroclimate variation in the hyperarid central Sahara

“…Green and orange contours along the southern Mediterranean coast delineate regions with respectively increased and reduced winter rainfall under a negative mode of the NAO ( 45 ). 1, Lake Sidi Ali ( 43 ); 2, Tassili N’Ajjer plateau ( 40 ); 3, Red Sea corals ( 62 ); 4, Saloum Delta shell middens ( 63 ); 5, Lake Bosumtwi ( 6 ); 6, Manga grasslands ( 5 ); 7, Lake Chad ( 2 ); 8, Lake Tizong ( 42 ). ( B ) Topography surrounding the deflation basins of Ounianga Kebir and Ounianga Serir at the base of the Erdi escarpment, with the estimated Early Holocene extent of both paleolakes (purple stippled lines) ( 15 , 23 ) and the extant lakes color coded according to their salinity (expressed as conductivity, in microsiemens per centimeter).…”