The composition of a ZnO (0001) polar surface irradiated with hydrogen ions has been investigated with the measuring temperature range from 22°C to 800°C. The surface has been analyzed by Auger electron spectroscopy for surface composition, X-ray photoelectron spectroscopy for chemical binding states, and reflection high energy electron diffraction for surface crystal structures and morphology. The surface oxygen concentration is found to increase at temperatures above 400°C. Reactions of oxygen with the hydrogen in the surface region are discussed with the results of the temperature programmed desorption. A model explaning the combined effects of oxygen segregation onto the surface, H₂ desorption, H₂O desorption and zinc atom evaporation is presented, by which the experimental results are well understood.