A great challenge in climate modelling is how to parametrize sub-grid cloud processes, such as autoconversion and accretion in warm rain formation. In this study, we use ground-based observations and retrievals over the Azores to investigate the so-called enhancement factors, E auto and E accr , which are often used in climate models to account for the influences of sub-grid variances of cloud and precipitation water on the autoconversion and accretion processes. E auto and E accr are computed at a variety of tempo-spatial scales corresponding to different model resolutions. The calculated E auto increase from 1.79 (0.5-hr/36 km) to 3.15 (3.5-hr/126 km), and the calculated E accr increases from 1.25 (0.5-hr/36 km) to 1.6 (5-hr/180 km). Comparing the prescribed enhancement factors to the values from observations shows that GCMs are using a much higher E auto (3.2) and lower E accr (1.07). This helps to explain why most of the GCMs produce too frequent precipitation events but with too light precipitation intensity. The ratios of rain to cloud liquid water at E accr = 1.07 and E accr = 2.0 are 0.048 and 0.119, respectively, further proving that the prescribed value of E accr = 1.07 used in GCMs is too small to simulate correct precipitation intensity. Both E auto and E accr increase when the boundary layer becomes less stable, and the values are larger in precipitating clouds (CLWP > 75 gm −2 ) than those in nonprecipiting clouds (CLWP < 75 gm −2 ). Therefore, the selection of E auto and E accr values in GCMs should be regime-dependent.