Discrepancies of kilometer-scale dynamic downscaling over the Tibetan Plateau: underestimation of nocturnal precipitation in summer

The diurnal variation in precipitation is an essential aspect of the hydrological cycle. It is also an effective way to assess the model performance and understand the local climate. However, there is still a lack of detailed evaluation and in-depth analyses of precipitation at the sub-daily scale for kilometer-scale dynamical downscaling simulations. In this study, we evaluated the precipitation outputs from quarter-degree dynamical downscaling modeling (28kmDDM) and kilometer-scale dynamical downscaling modeling (4kmDDM) at the sub-daily scale over the Tibetan Plateau (TP) during the summer of 2014. The advantages and disadvantages of kilometer-scale simulation are well-dissected. Our findings indicated that 4kmDDM is clearly advantageous for capturing daily-scale precipitation features, primarily due to its superior ability to simulate convective precipitation during the day. On the contrary, compared to the station observations, 4kmDDM exhibits a nocturnal underestimation, particularly in the southeastern basins of the TP, where steep topographic relief exists. Compared to 28kmDDM, 4kmDDM simulates more realistic surface air temperatures and abundant precipitable water vapor. However, the formation of low-level clouds in 4kmDDM is limited due to insufficient condensation. Under stable nocturnal stratification, 4kmDDM lacks the potential to trigger more condensation in the middle and high layers without low-level condensation latent heating. Fewer clouds and hydrometeors are the primary factors contributing to nocturnal precipitation underestimation. This study highlights the discrepancies of the kilometer-scale simulation in nocturnal precipitation under stable stratification.