The evolution of mesoscale convective systems (MCSs) leading to a heavy rainstorm event that occurred in Beijing on 21 July 2012 was simulated using the Weather Research and Forecasting model. Observational analyses indicated that this event can be divided into an earlier‐occurring warm‐sector precipitation (WSP) and a later‐occurring cold‐frontal precipitation (CFP). Owing to the considerable differences in their ambient weather conditions, the features and evolution of the cloud microphysics were different. Diagnoses of the mass‐ and heat‐hydrometeor budgets showed that the major differences in rainwater source were that the graupel melting (PGMLT) and the collection of snow by rain (PRACS_s2r) had similar magnitudes in the WSP, and PGMLT was larger than PRACS_s2r in the CFP, while the accretion growth of cloud droplets (PRA) was always the largest in both phases. The main cooling effect in the WSP was due to the evaporation of rainwater (PRE) and cloud water, while it was PRE and PGMLT for the CFP. The mechanisms of how microphysical processes influenced the precipitation were explored. It was found that the strong PRA in the WSP was conducive to the formation of a supercooled water level and evoked a seeding effect. However, graupel processes were crucial for the CFP. The strong sublimation processes of graupel and snow associated with the collection of droplets by graupel caused more latent heat release and drove airflow to reach a higher convection height. Moreover, the stronger PGMLT cooled the air in the MCS and reduced the effect of cloud droplet accretion growth.

A heavy rainfall event that occurred in Beijing on July 21, 2012 was simulated successfully using the Weather Research and Forecasting model, and the precipitation efficiency (PE) during different rainfall stages was studied. The results showed that both the large‐scale precipitation efficiency (LSPE) and the cloud‐microphysics precipitation efficiency (CMPE) in the peak of the warm sector stage (T1) were significantly higher than those in the cold front stage (T2). The higher LSPE was related to the water vapor advection, which played a positive role in T1 due to the warm and moist advection in the lower troposphere, and a negative role in T2 because of the cold and dry airflow in the middle level. The snow‐related microphysical processes had similar tendencies to the CMPE, in which the higher rain–snow collection and deposition of water vapor brought about the higher CMPE in T1. Analysis of the underlying mechanisms proved that the LSPE and CMPE were subject to the large‐scale environment and cloud microphysical features.

Compared with conventional pumped-storage hydroplants, seawater pumped-storage hydroplants are constructed in a complex marine environment. The wave disturbance may affect the safety operation of the pump turbine in the seawater pumped hydroplant via affecting the level of the free water surface. To explore the effect of wave disturbance on the operation of the pump turbine in a seawater pumped-storage hydroplant, assuming that the wave disturbance follows a sine function, on the basis of Airy’s micro-amplitude wave theory and the comprehensive characteristic curve of a pump turbine, we use sliding grid technology and the SST k–ω turbulence model to simulate the dynamics of fluid in a full-flow channel. In this study, the unsteady flow field, Q-criterion vorticity, relative pressure pulsation amplitude, and frequency of pressure pulsation are analyzed to determine the internal flow field and pressure pulsation under different wave disturbance conditions and operating loads. The results show that both the pressure pulsation in the pump turbine and its frequency domain are affected by the wave disturbance. In addition, the turbulent flow with a large flow rate tends to produce higher relative pressure pulsation under wave disturbance. Due to the large flow rate and strong static and dynamic interference in the vaneless area, the relative amplitude of the pressure pulsation is significantly affected by wave disturbance. Furthermore, the low-frequency pressure pulsation of the draft tube is superimposed with the wave disturbance frequency.

The safe operation of drainage pumping stations, which are core flood-control facilities in eastern coastal areas of China, is paramount due to frequent typhoons and short-duration heavy rainfall. To enhance the operational safety against water hammer during pump trips caused by power failure, a water hammer protection method based on the combined application of flap valves and sluice gates is proposed. Only the scenario of all pumps tripping simultaneously was considered. A one-dimensional simulation model of the pumping station’s hydraulic transient process, which included pumps, pipelines, flap valves, and sluice gates, was established to analyze the system response under three scenarios: (i) only the flap valve closes normally, with the sluice gates remaining open, (ii) the flap valve fails, only the sluice gates operate, and (iii) the combined application of flap valve and sluice gates. In scenario (i), the maximum and minimum channel pressure heads were 13.53 m and −2.22 m, respectively, with no pump reversal occurred. However, continuous pressure fluctuations were observed downstream of the flap valve, posing a threat to the flow channel’s safety. In scenario (ii), the channel pressure heads all met the control requirements. Employing a 60 s single-stage linear closure rule for Gate #1 maintained the pump’s reverse speed within the safe range, peaking at −147.25% of the rated speed, with a reversal duration of 60 s. In scenario (iii), all channel pressure heads met basic control requirements, and no pump reversal occurred. The optimal strategy was found to be the adoption of a 60 s single-stage linear closure rule for both sluice gates. Compared to the scenario (i), the combined application reduced the amplitude of pressure fluctuations and damped these fluctuations rapidly, thus shortening the oscillation duration. The combined approach innovatively utilizes existing infrastructure for water hammer control, providing an economical and reliable solution for water hammer protection in urban drainage pumping stations.

A torrential rainfall that occurred in Beijing during the period of 21–22 July 2012 is simulated by the Weather Research and Forecasting Model in order to investigate the probable mechanisms for the initiation and organization of warm-sector mesoscale convective systems (MCSs). The simulated results show that the cyclone, which formed in Hetao area, Inner Mongolia and moved eastward slowly, played a key role in the formation and development of warm-sector precipitation, although the favorable atmospheric environment and the configuration of weather systems are also important, which caused the trigger and organization of convective cells along Taihang Mountains. It is the interaction of the local terrain convergence line and the southerly airflows of Hetao cyclone that cause the continuous trigger of convective cells along Taihang Mountains. While, the triggers of convective cells in the plains are caused by the gravity waves, which is related to the development and eastward movement of Hetao cyclone. It must be pointed out that the merging and coupling between the cells that triggered in Taihang Mountains and moved southwesterly and the cells that triggered in plains and moved northeasterly are the key factors for the formation and development of MCSs during the warm-sector precipitation. In addition, the back-building processes and the cold pool forcing are also important for the formation and development of MCSs in this study.

This study on the warm-sector heavy rainfall event in Guangzhou on 7 May 2017, examined the effects and mechanisms of incorporating 30 m high-resolution land surface data into its numerical simulation. The updated 1km numerical model, integrating 30 m high-resolution land surface data, successfully captured the initiation, back-building, and organized development of warm-sector convections in Huadu and Zengcheng District. The analysis revealed that the high spatial resolution of the surface data led to a reduced urban area footprint (urban −6.31%), increased vegetation cover (forest 11.63%, croplands 1%), and enhanced surface runoff (water 2.77%) compared with a model’s default land cover (900 m). These changes mitigated the urban heat island (UHI) effect within the metropolitan area and decreased the surface sensible heat flux. This reduction contributed to a pronounced temperature gradient between Huadu Mountain and the urban area. Additionally, a stronger high-pressure recirculation and sea–land breezes facilitated the transport of warm and moist air from the sea inland, creating a humid corridor along the sea–land interface. The consistent influx of warm and moist air near the mountain front, where strong temperature gradients were present, forcibly triggered warm-sector convection, intensifying its organization. This study highlighted the critical role of high-resolution land surface data in the accurate numerical simulation of warm-sector heavy rainfall.