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The latitudinal distribution of starspots deviates from the solar patternwith increasing rotation rate. Numerical simulations of magnetic flux emergenceand transport can help model the observed stellar activity patterns and theassociated brightness variations. We set up a composite model for the processesof flux emergence and transport on Sun-like stars, to simulate stellarbrightness variations for various levels of magnetic activity and rotationrates. Assuming that the distribution of magnetic flux at the base of theconvection zone follows solar scaling relations, we calculate the emergencelatitudes and tilt angles of bipolar regions at the surface for variousrotation rates, using thin-flux-tube simulations. Taking these two quantitiesas input to a surface flux transport SFT model, we simulate thediffusive-advective evolution of the radial field at the stellar surface,including effects of active region nesting. As the rotation rate increases, (1)magnetic flux emerges at higher latitudes and an inactive gap opens around theequator, reaching a half-width of $20^\circ$ for $8\Omega_\odot$, (2) the tiltangles of freshly emerged bipolar regions show stronger variations withlatitude. Polar spots can form at $8\Omega_\odot$ by accumulation offollower-polarity flux from decaying bipolar regions. From $4\Omega_\odot$ to$8\Omega_\odot$, the maximum spot coverage changes from 3 to 20%, respectively,compared to 0.4% for the solar model. Nesting of activity can lead to stronglynon-axisymmetric spot distributions. On Sun-like stars rotating at$8\Omega_\odot$ ($P_{\rm rot}\simeq 3$ days), polar spots can form, owing tohigher levels of flux emergence rate and tilt angles. Defining spots by athreshold field strength yields global spot coverages that are roughlyconsistent with stellar observations.

Forward modelling of brightness variations in Sun-like stars I. Emergence and surface transport of magnetic flux