Preprints
https://doi.org/10.5194/cp-2021-129
https://doi.org/10.5194/cp-2021-129

  05 Oct 2021

05 Oct 2021

Review status: this preprint is currently under review for the journal CP.

Simulated range of mid-Holocene precipitation changes to extended lakes and wetlands over North Africa

Nora Farina Specht1, Martin Claussen1,2, and Thomas Kleinen1 Nora Farina Specht et al.
  • 1Max Planck Institute for Meteorology, Bundesstrasse 53, 20146 Hamburg, Germany
  • 2Meteorological Institute, Centrum für Erdsystemforschung und Nachhaltigkeit (CEN), Universität Hamburg, Bundesstrasse 55, 20146 Hamburg, Germany

Abstract. Enhanced summer insolation over North Africa induced a monsoon precipitation increase during the mid-Holocene, about 6000 years ago, and led to a widespread expansion of lakes and wetlands in the present-day Sahara. This expansion of lakes and wetlands is documented in paleoenvironmental sediment records, but the spatially sparse and often discontinuous sediment records provide only a fragmentary picture. Former simulation studies prescribed either a small lake and wetland extent from reconstructions or focused on documented mega-lakes only to investigate their effect on the mid-Holocene climate. In contrast to these studies, we investigate the possible range of mid-Holocene precipitation changes in response to a small lake extent and a potential maximum lake and wetland extent. 

Results show that the maximum lake and wetland extent shift the North African rain belt about 3 ° farther northward than the small lake extent. Vegetated wetlands cause a larger precipitation increase than the equally-large lakes due to their high surface roughness. A moisture budget analysis reveals that both, lakes and wetlands, cause an enhanced inland moisture transport and local moisture recycling to their southern side. In contrast, increased moisture advection by the Harmattan winds causes a drying response to the north of the lakes and wetlands. These results indicate that the latitudinal position of the lakes and wetlands influences the northward extension of the African summer monsoon. In the sensitivity experiments, the northern position of West Saharan lakes and wetlands substantially contributes to the strong monsoon northward shift seen in the maximum lake and wetland simulations.

Nora Farina Specht et al.

Status: open (until 30 Nov 2021)

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Nora Farina Specht et al.

Nora Farina Specht et al.

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Short summary
Palaeo-environmental records only provide a fragmentary picture of the lake and wetland extent in North Africa during the mid-Holocene. Therefore, we investigate the possible range of mid-Holocene precipitation changes caused by an estimated small and maximum lake extent and a maximum wetland extent. Results show a particularly strong monsoon precipitation response to lakes and wetlands over the Western Sahara and an increased monsoon precipitation when replacing lakes with vegetated wetlands.