\usepackage{imakeidx}

%% Index entries (italic font for files, preformat for code)
\newcommand{\hf}[1]{   \index{h90 files!#1}             \textit{#1.h90}          }
\newcommand{\ifile}[1]{\index{Input NetCDF files!#1.nc} \textit{#1.nc}           }
\newcommand{\jp}[1]{   \index{Model parameters!#1}      \texttt{#1}              }
\newcommand{\key}[1]{  \index[keys]{#1@\texttt{\textbf{key\_#1}}} \texttt{\textbf{key\_#1}}}
\newcommand{\mdl}[1]{  \index[modules]{#1@\textit{#1.F90}}        \textit{#1.F90}          }
\newcommand{\nam}[1]{  \index[blocks]{#1@\texttt{\&nam#1}}        \forcode{&nam#1}         }
\newcommand{\np}[1]{   \index[parameters]{#1@\texttt{#1}}         \texttt{#1}              }
\newcommand{\npnew}[2][]{\index[parameters]{#2@\texttt{#2}}       \forcode{#2#1}           }
\newcommand{\rou}[1]{  \index[subroutines]{#1@\texttt{#1}}        \texttt{#1}              }

\indexsetup{toclevel=section, othercode=\small}

\makeindex[intoc=true, name=blocks     , title=Namelist blocks      , columns=3]
\makeindex[intoc=true, name=keys       , title=CPP keys                        ]
\makeindex[intoc=true, name=modules    , title=\fortran\ modules    , columns=3]
\makeindex[intoc=true, name=parameters , title=Namelist parameters  , columns=3]
\makeindex[intoc=true, name=subroutines, title=\fortran\ subroutines           ]