Representation of Multidecadal Sahel Rainfall Variability in 20th Century Reanalyses

Abstract

Summer rainfall in the Sahel region has exhibited strong multidecadal variability during the 20th century causing dramatic human and socio-economic impacts. Studies have suggested that the variability is linked to the Atlantic multidecadal variability; a spatially persistent pattern of warm/cold sea surface temperatures in the North Atlantic. In the last few years, several promising century-long reanalysis datasets have been made available, opening up for further studies into the dynamics inducing the observed low-frequency rainfall variability in Sahel. We find that although three of the 20th century ECMWF reanalyses show clear multidecadal rainfall variability with extended wet and dry periods, the timing of the multidecadal variability in two of these reanalyses is found to exhibit almost anti-phase features for a large part of the 20th century when compared to observations. The best representation of the multidecadal rainfall variability is found in the ECMWF reanalysis that, unlike the other reanalyses (including NOAA’s 20th century), do not assimilate any observations and may well be a critical reason for this mismatch, as discussed herein. This reanalysis, namely ERA-20CM, is thus recommended for future studies on the dynamics driving the multidecadal rainfall variability in Sahel and its linkages to the low-frequency North Atlantic oceanic temperatures.

Farmers’ Perceptions of Climate Change and Agricultural Adaptation in Burkina Faso

“…These values were in line with studies providing longer datasets , showing a precipitation reduction (25%) and higher variability in southernmost parts of the country [5]. In addition, the 20th century reanalysis exhibited a clear multidecadal rainfall variability within the Sahel region [41]; while increasing interannual rainfall variability was reported since the 1960s, due to changes in rainfall patterns and decreases in total annual rainfall [7]. Our study showed a strong decline in annual rainfall between 1973-1982 and 2003-2012 periods in central and northernmost parts of the country, but with a rainfall recovery since 2006.…”

The Tropical Atlantic Observing System

“…There was a period of severe drought between the 1960s and 1980s that strongly impacted West African agriculture and economies. Rainfall in the Sahel has increased since the 1980s, but has not recovered to pre-drought levels (Nicholson et al, 2000;Dong and Sutton, 2015;Berntell et al, 2018). Through its impacts on soil moisture, vegetation, and albedo, the rainfall received during a given year affects the likelihood of drought the following year, acting to enhance decadal-multidecadal variations of Sahel rainfall (Zeng et al, 1999).…”

Impacts of Large‐Scale Sahara Solar Farms on Global Climate and Vegetation Cover

“…Past studies (Hazeleger et al., 2010, 2012; Kageyama et al., 2017) provide an overview of the general performance of an earlier version of this model. In particular, the model demonstrates skill in emulating a number of key physical processes relevant to this study, such as the atmospheric general circulation and monsoon system (Berntell et al., 2018; Pausata et al., 2016) and the tropical climate variability and atmospheric teleconnections (Pausata et al., 2017a). A recent study shows that simulated 100‐year trends and interdecadal variability of EC‐Earth (EC‐Earth3‐Veg configuration, also used in this study) fall within the range of the CMIP6 (the latest ESM Intercomparison project) piControl ensemble (Parsons et al., 2020).…”