19 Sep 2022
19 Sep 2022
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

How does the explicit treatment of convection alter the precipitation-soil hydrology interaction in the Holocene African humid period?

Leonore Jungandreas1,a, Cathy Hohenegger1, and Martin Claussen1,2 Leonore Jungandreas et al.
  • 1Max Planck Institute for Meteorology, Bundesstraße 53, 20146 Hamburg
  • 2Center for Earth System Research and Sustainability, Universität Hamburg, Bundesstraße 53, 20146 Hamburg
  • anow at: German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig

Abstract. Global climate models with coarse horizontal resolution are largely unable to reproduce the monsoonal precipitation pattern over North Africa during the mid-Holocene. Here we present the first regional, storm-resolving simulations with an idealized but reasonable mid-Holocene vegetation cover. In these simulations, the West African monsoon expand farther north by about 4–5° and the precipitation gradient between the Guinea coast and the Sahara decreases in comparison to simulations with a barren Sahara as it is today. The northward shift of monsoonal precipitation is caused by land surface – atmosphere interaction, i.e. the coupling of soil moisture and precipitation as well as interactions of the land surface with the large-scale monsoon circulation (e.g. the African easterly jet).

We find a similar response of the monsoon circulation to an increase in vegetation cover in simulations with parameterized convection. Moreover, changes are even larger than in simulations with explicitly resolved convection (i.e. the storm-resolving simulations). We attribute the differences in monsoonal precipitation to differences in soil moisture that are strongly controlled by runoff and the precipitation characteristics as previously shown in Jungandreas et al. (2021).

We confirm this by performing simulations with a constant soil moisture field in both explicitly resolved and parameterized convection simulations. In these simulations, explicitly resolved convection simulations expand precipitation as far north as parameterized convection simulations. This study thus highlights the importance of the type of rainfall in modulating land- atmosphere feedbacks, instead of only considering the amount of rainfall. Moreover, this study suggests that comprehensive land-surface schemes, which properly respond to varying precipitation characteristics, are needed for studying land-surface – atmosphere interaction

Leonore Jungandreas et al.

Status: open (until 14 Nov 2022)

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Leonore Jungandreas et al.

Leonore Jungandreas et al.


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Short summary
Increasing the vegetation cover over mid-Holcocene North Africa expands the West African Monsoon ~ 4–5° further north. This northward shift of monsoonal precipitation is caused by interactions of the land surface with the large-scale monsoon circulation and the coupling of soil moisture to precipitation. We highlight the importance to not only consider how soil moisture influences precipitation but also how different precipitation characteristics alter the soil hydrology via runoff generation.