In this work we investigate how the low-energy unoccupied electronic structure of bulk BaBiO${}_3$ is modulated by temperature and oxygen vacancies. Using oxygen K-edge X-ray absorption spectroscopy (XAS), we find a sizable temperature dependence of the measured spectra, with an important modification of the pre-edge peak line-shape, which might be associated with the coupling between the excited electron and the anharmonic lattice dynamics of BaBiO${}_3$. Thermal treatment significantly affects the spectral profile, particularly by suppressing the pre-edge peak, but our density functional theory calculations suggest that oxygen vacancies alone cannot fully account for the observed spectral modifications.