The mesoscale Weather Research and Forecasting (WRF) model has been widely employed to forecast day-ahead rainfalls. However, the deterministic predictions from the WRF model incorporate relatively large errors due to numerical discretization, inaccuracies in initial/boundary conditions and parameterizations, etc. Among them, the uncertainties in parameterization schemes have a huge impact on the forecasting skill of rainfalls, especially over the Sichuan Basin which is located east of the Tibetan Plateau in southwestern China. To figure out the impact of various parameterization schemes and their interactions on rainfall predictions over the Sichuan Basin, the Global Forecast System data are chosen as the initial/boundary conditions for the WRF model and 48 ensemble tests have been conducted based on different combinations of four microphysical (MP) schemes, four planetary boundary layer (PBL) schemes, and three cumulus (CU) schemes, for four rainfall cases in summer. Compared to the observations obtained from the Chinese ground-based and encrypted stations, it is found that the Goddard MP scheme together with the asymmetric convective model version 2 PBL scheme outperforms other combinations. Next, as the first step to explore further improvement of the WRF physical schemes, the polynomial chaos expansion (PCE) approach is then adopted to quantify the impacts of several empirical parameters with uncertainties in the WRF Single Moment 6-class (WSM6) MP scheme, the Yonsei University (YSU) PBL scheme and the Kain-Fritsch CU scheme on WRF rainfall predictions. The PCE statistics show that the uncertainty of the scaling factor applied to ice fall velocity in the WSM6 scheme and the profile shape exponent in the YSU scheme affects more dominantly the rainfall predictions in comparison with other parameters, which sheds a light on the importance of these schemes for the rainfall predictions over the Sichuan Basin and suggests the next step to further improve the physical schemes.

Knowledge of the microphysical characteristics of precipitation plays a significant role in meteorology, hydrology, and natural hazards management, especially in the western Sichuan Basin (WSB), which is located east of the Tibetan Plateau (TP) in southwestern China and thus has unique terrain conditions and weather systems. Nonetheless, the literature regarding raindrop size distribution (RSD) in the WSB is still very limited. This work investigates RSD characteristics and temporal variations in a site (Chengdu, CD) of the WSB by employing three years of quality-controlled RSD observation collected from a second-generation PARSIVEL disdrometer. The results show that RSD has noticeable seasonal and diurnal variations in CD. Specifically, the broadest mean raindrop spectra can be found in summer and the narrowest in winter, and the raindrop spectra of a day can be the narrowest during 1400–1500 BJT (Beijing Standard Time, UTC+8). In addition, the mass-weighted mean diameter ($D_m$) is lower in the daytime than in the nighttime, while the logarithm of the generalized intercept parameter ($lo{g}_{10}$N_w, the unit of the N_w is m⁻³ mm⁻¹) has a larger value in the daytime than in the nighttime. In addition, intercomparisons indicate that the mean $D_m$ of convective rains in CD is smaller than in South China and it is higher than in the eastern slope of TP, East China, and North China; on the other hand, the corresponding mean $lo{g}_{10}{N}_w$ is close to the value at the middle TP. Local empirical relations of shape–slope parameters ($\mu$–$\Lambda$) and reflectivity–rain rate (Z–R) are also presented to provide references for optimizing the RSD parameterization scheme and radar precipitation estimation in the local area.

Previous research has primarily focused on assessing seasonal mean or annual extreme climate events, whereas intraseasonal variability in extreme climate has received comparatively little attention, despite its importance for understanding short-term climate dynamics and associated risks. This study evaluates the performance of nine climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in reproducing summer maximum temperature (Tmax) variability across China during 1979–2014, with the variability defined as the standard deviation of daily Tmax anomalies for each summer. Results show that most CMIP6 models fail to reproduce the observed north–south gradient of Tmax variability with significant regional biases and limited agreement on temporal trends. The multi-model ensemble (MME) outperforms most individual models in terms of root-mean-square error and spatial correlation, but it still under-represents the observed temporal trends, especially over southeastern and central China. Taylor diagram analysis reveals that EC-Earth3, GISS-E2-1-G, IPSL-CM6A-LR, and the MME perform relatively well in capturing the spatial characteristics of Tmax variability, whereas MIROC6 shows the poorest performance. These findings highlight the persistent limitations in simulating intraseasonal Tmax variability and underscore the need for improved model representations of regional climate dynamics over China.

During the past three years, new insights have been gained into the convective features and microphysical characteristics of heavy rainfall in South China, which is a typical monsoon coastal area. Such improved understanding is closely related to the rapid progress of application of advanced remote sensing techniques, in particular the upgrade of the dual-polarization function of the operational weather radars in South China. This paper reviews the representative studies since approximately 2019 in three aspects. First, spatiotemporal distribution and diurnal propagation of the convection initiation during the warm season. Second, general features and synoptic-scale environments of the meso-β-scale convective systems (MCSs) during the pre-summer rainy season (April to June). Third, microphysical characteristics of the extreme short-term rainfall and the coexisting frontal and warm-sector heavy rainfall in South China.

In July 2024, a severe rainfall event struck Sichuan Province, Southwest China, triggering deadly landslides and causing significant societal impacts. This study investigates the spatiotemporal characteristics and underlying mechanisms of the event using high-resolution surface observations, radar reflectivity, and ERA5 reanalysis data. The rainfall exhibited distinct mesoscale organization, with two primary precipitation centers identified: subregion A located within the plateau-lain transitional zone of the western Sichuan Basin, and subregion B situated over the Chengdu Plain. Synoptic-scale analysis indicated that the rainfall developed under favorable large-scale atmospheric conditions, including a mid-tropospheric trough, a pronounced low-level jet, and a well-defined Southwest Vortex (SWV), which is a dominant lower-tropospheric circulation system in this region. The evolution of rainfall was closely tied to the initiation and subsequent eastward progression of the SWV. The rainfall-producing mesoscale convective system (MCS) first formed over subregion A at approximately 2300 BST (UTC + 8) on 19 July. Vorticity budget diagnostics revealed that vertical advection and low-level convergence significantly contributed to vortex intensification during this initial phase, closely associated with the orographic lifting of low-level airflow. Convective activity in subregion B commenced roughly four hours later, coinciding with the eastward propagation of the SWV, during which horizontal vorticity advection became the primary mechanism sustaining the vortex. After 1400 BST on 20 July, the SWV weakened significantly, leading to the dissipation of the MCS and the cessation of rainfall.

 South China is one of China’s rainiest regions, where mesoscale convective systems (MCSs) frequently produce heavy rainfall during the post-flood rainy season (July-September). Using 1-km, 6-min radar mosaics and ERA5 reanalysis, this study identified 123 MCSs from 2019 to 2022. MCS activity is concentrated over southern Guangxi (S-GX) and the Pearl River Delta (PRD), with marked regional contrasts in diurnal evolution and environmental conditions. Variations in the relative positions of the South Asian High (SAH) and the western North Pacific subtropical high (WNPSH) produce distinct circulation regimes over the two regions. S-GX MCSs over the S-GX mainly form from midnight to early morning and are associated with an eastward-extended SAH and a westward-displaced WNPSH, which strengthen the southerly monsoonal flow and produce a deeper moisture transport layer extending to approximately 750 hPa. Together with larger convective instability (mean CAPE ≈ 1843 J kg⁻¹), these conditions allow convection to overcome the relatively larger convective inhibition (CIN) and support nocturnal MCS development. In contrast, PRD MCSs over the PRD mainly form from afternoon to evening under weaker large-scale forcing, shallower moisture transport largely confined below 900 hPa, lower but localized instability (mean CAPE ≈ 1523 J kg⁻¹) and smaller inhibition. These conditions increased the relative importance of daytime boundary-layer heating and sea-breeze convergence, consistent with the afternoon to evening MCS maximum. The results identify a synoptic-dynamical mode over S-GX and a boundary-layer thermodynamic mode over the PRD, providing a physical framework for understanding post-flood-season MCS development and heavy rainfall over South China.