Can Sub-Daily Multivariate Bias Correction of Regional Climate Model Boundary Conditions Improve Simulation of the Diurnal Precipitation Cycle?

The diurnal cycle is often poorly reproduced in global climate model (GCM) simulations, particularly in terms of rainfall frequency and amplitude. While improvements in the regional climate model (RCM) with bias-corrected boundaries have been reported in previous studies, they assumed that diurnal patterns are simulated correctly by the GCM, potentially leading to inaccuracies in the maximum rainfall timing and magnitude within the RCM domain. Here we provide the first examination of improvements to the diurnal cycle, within a RCM domain, achieved through the use of sophisticated bias-corrected lateral and lower boundary conditions. Results show that the RCMs with bias-corrected boundaries generally present improvement in capturing both rainfall timing and magnitude, particularly in northern Australia, where a strong diurnal pattern in rainfall is prevalent. We show that correcting systematic sub-daily multivariate bias in RCM boundaries improves the diurnal rainfall cycle, which is particularly important in regions where short-term intense precipitation occurs. Global climate models have limitations in simulating precipitation characteristics at sub-daily time scales, leading to significant bias in capturing rainfall timing and magnitude in regional climate model (RCM) simulations that use global climate model data as input. Previous studies have applied various bias correction approaches to the boundary conditions of RCMs, but they often assume that GCM sub-daily rainfall patterns are simulated correctly, leading to a significant bias in maximum rainfall timing and magnitude within the domain. This study investigates the consequences of multivariate sub-daily bias correction on the boundary conditions in order to evaluate the model performance for short-term precipitation events. The results show that RCMs with bias-corrected boundary conditions exhibit improvement across Australia, especially in northern Australia, which regularly experiences intense sub-daily rainfall. Regional climate model (RCM) with uncorrected boundaries poorly represented 3-hourly precipitation with only 20%similar to 30% agreements compared to observationsSub-daily bias correction of RCM lateral boundaries improves the sub-daily representation of fields entering the RCM domainSub-daily multivariate bias correction on the boundaries resulted in additional improvements, especially in northern Australia

Automated summary

Global climate models have limitations in simulating the diurnal cycle, but improvements can be achieved through bias-corrected regional climate models. By correcting the boundary conditions, particularly in regions with significant diurnal rainfall, the diurnal pattern of rainfall can be more accurately simulated. Correcting systematic sub-daily multivariate biases in the boundary conditions is particularly important for short-term intense precipitation events in regional climate models.