  We obtain an analytical expression for the linewidth of the 1s-exciton as a
function of temperature in transition metal dichalcogenides. The total
linewidth, as function of temperature, is dominated by three contributions: (i)
the radiative decay (essentially temperature independent); (ii) the
phonon-induced intravalley scattering; (iii) the phonon-induced intervalley
scattering. Our approach uses a variational \emph{Ansatz} to solve the Wannier
equation allowing for an analytical treatment of the excitonic problem,
including rates of the decay dynamics. Our results are in good agreement with
experimental data already present in the literature and can be used to readily
predict the value of the total linewidth at any temperature in the broad class
of excitonic two-dimensional materials.
