Water has been pushed into the basement light well here; an initial analysis showed: Water was flushed into the well by the strong wind and heavy rain, and it can't seep away that quickly. About 500ml of water is thus present around the window seal. I blotted it up with a cloth.
However: If such a situation lasts for several hours, the basement would probably be well underwater. I will now build a light well cover for these cases and then lay it on.
Otherwise, the humidity in the basement is high, about 68%. I am now running the dehumidifier. Washing and drying laundry also contributes to it...