i want the second "diffusivity" verticallay centered within its obvious scope 
MWE
\documentclass{scrreprt} \usepackage{amsmath} \begin{document} \begin{table} \centering \begin{tabular}{c c c c} \hline Variable &Region Variable &Value &Unit \\ \hline area &$A$ &0 &m\\ \hline &$L_{1}$ &0 &m\\ lengths &$L_{2}$ &0 &m\\ &$L_{3}$ &0 &m\\ \hline &$D_{1}$\\ diffusivity &$D_{2}$\\ &$D_{3}$\\ \hline diffusivity &$D_{1}$\\ &$D_{2}$\\ \hline \end{tabular} \caption{xyz} \label{tab:para} \end{table} \end{document} 

multirow: ctan.org/pkg/multirow (BTW the package needs some improvements)