We consider a periodic-parabolic eigenvalue problem with a
non-negative potential vanishing on a non-cylindrical
domain satisfying conditions similar to those for the parabolic
maximum principle. We show that the limit as
leads to a periodic-parabolic problem on having a unique
periodic-parabolic principal eigenvalue and eigenfunction. We
substantially improve a result from
[Du &
Peng, Trans. Amer. Math. Soc. 364 (2012), p. 6039–6070]. At the
same time we offer a different approach based on a periodic-parabolic
initial boundary value problem. The results are motivated by an
analysis of the asymptotic behaviour of positive solutions to
semilinear logistic periodic-parabolic problems with temporal and
spacial degeneracies.