In the upper panels, the normalised redshift distributions, P(z), for each tomographic bin (S1 to S5). The redshift distribution from the entire KiDS-1000 DR4 galaxy sample, P_total(z), is shown in black, while the other ten redshift distributions are derived from 10 equi-populated subsamples of DR4 based on their observational depth (i.e. the mean value of the root-mean-square of the background noise, ${\overline{\sigma }}_{\mathrm{rms}}$) which is shown with its respective colour. The lower panels show the associated residual change in the redshift distributions with respect to P_total(z) per unit redshift. It is apparent that variable depth mostly affects the source distributions at high redshifts, while the effect tends to decrease the mean of the redshift distribution with increasing σ_rms.