Abstract. Global climate models experience difficulties in simulating the northward extension of the monsoonal precipitation over north Africa during the mid-Holocene as
revealed by proxy data. A common feature of these models is that they usually
operate on grids that are too coarse to explicitly resolve convection, but convection
is the most essential mechanism leading to precipitation in the West African
Monsoon region. Here, we investigate how the representation of tropical deep
convection in the ICOsahedral Nonhydrostatic (ICON) climate model affects the meridional distribution of
monsoonal precipitation during the mid-Holocene by comparing regional
simulations of the summer monsoon season (July to September; JAS) with
parameterized and explicitly resolved convection. In the explicitly resolved convection simulation, the more localized nature of precipitation
and the absence of permanent light precipitation as compared to the
parameterized convection simulation is closer to expectations. However, in the JAS mean,
the parameterized convection simulation produces more precipitation and extends further
north than the explicitly resolved convection simulation, especially between 12 and
17∘ N. The higher precipitation rates in the parameterized convection
simulation are consistent with a stronger monsoonal circulation over
land. Furthermore, the atmosphere in the parameterized convection simulation is less
stably stratified and notably moister. The differences in atmospheric water
vapor are the result of substantial differences in the probability
distribution function of precipitation and its resulting interactions with the
land surface. The parametrization of convection produces light and large-scale
precipitation, keeping the soils moist and supporting the development of
convection. In contrast, less frequent but locally intense precipitation
events lead to high amounts of runoff in the explicitly resolved convection
simulations. The stronger runoff inhibits the moistening of the soil during
the monsoon season and limits the amount of water available to evaporation in
the explicitly resolved convection simulation.