documentclass[landscape]{scrartcl}
setparsizes{0pt}{0pt}{0pt plus 1fil}
usepackage[showframe=true]{geometry}
  usepackage{scrlayer-scrpage}

begin{document}
newgeometry{headheight=3baselineskip,
margin=3cm,
includehead,
headsep=0mm,
}
333 chead{111 \ aaa \ bbb}
newpage

newgeometry{  headheight=2baselineskip,
margin=3cm,
includehead,
headsep=0mm,
}
222  chead{222 \ aaa }
newpage

newgeometry{headheight=4baselineskip,
margin=3cm,
includehead,
headsep=0mm,
}
444 chead{444 \ aaa \ bbb \ ccc}
newpage

end{document}