Assessing Biases and Climate Implications of the Diurnal Precipitation Cycle in Climate Models

Abstract

The diurnal cycle is a common benchmark for evaluating the performance of weather and climate models on short timescales. For decades, capturing the timing of peak precipitation during the day has remained a challenge for climate models. In this study, the phase and amplitude of the diurnal precipitation cycle in Coupled Model Intercomparison Project (CMIP) models are compared to satellite data. While some improvements align CMIP6 models closer to satellite observations, significant biases in the timing of peak precipitation remain, especially over land. Notably, precipitation over land in CMIP6 models still occurs ∼5.4 h too early; the diurnal cycle amplitude is ∼0.81 mm day⁻¹ too small over the oceans. Further, the diurnal phase of oceanic precipitation correlates weakly with the equilibrium climate sensitivity in CMIP6 models: models with a later precipitation peak over oceans tend to exhibit a higher climate sensitivity. However, it is unclear whether this relationship is robust.