Abstract The three-river-source (TRS) region in the hinterland of the Qinghai–Tibet Plateau over China is often affected by heavy rainfall and even disasters associated with mesoscale convective systems (MCSs). Using an MCS dataset established by hourly equivalent blackbody temperature T BB data of FY-2 series geostationary meteorological satellites and ERA5 reanalysis data in the warm season (May–August) from 2005 to 2020, the moist potential vorticity (MPV) mechanism for generating MCSs in the TRS is analyzed. Under the influences of weather systems such as midlevel trough and subtropical high and high-level South Asian high and westerly jet, the positive promotion effect of relative MPV (RMPV) on MCSs is quite apparent and is most effective near the midlevel frontal zone. The background MPV of atmosphere (AMPV) provides favorable environmental energy. RMPV is the power source to convert unstable energy into kinetic energy for MCS generation through promoting the development of moist baroclinicity and the creation of slantwise upward motion and then organizing convection, with moisture transport of lower-level easterly anomaly being a signal. The barotropic term ( ζ MPV) identifies the location of the MCS generation, and the baroclinic term (SMPV) is the dynamical supporter for the “vortex source.” The convergence near 500 hPa between high-level westerly jet and low-level southeasterly jet serves as an important driving force for MCS generation, while heating is an important exogenous accelerator in energy conversion.

East China is one of the source regions of the extratropical cyclones (ECs) over East Asia, whose generation and evolution significantly influence weather patterns in local and surrounding areas. Based on the ERA5 reanalysis data during 1979-2022 and the objective identification method for extratropical cyclogenesis (EC-genesis), the minimum geopotential height at 850 hPa and vertical relative vorticity here are viewed as the center and intensities of EC-genesis, respectively. Statistical analysis shows that the intensity of EC-genesis in East China has remained stable over the past 44 years, but the horizontal convergence has decreased significantly under the stable pattern. In order to understand such patterns, we employed the moist C-vector diagnosis. This method allows us to investigate the factors driving the vertical motion and horizontal convergence from the perspective of the destruction and restoration of the thermal wind balance, and the factors leading to the EC-genesis from the perspective of the destruction and restoration of the geostrophic balance. It is found that the ascent motion driven by the diabatic effect decreases between 750-350 hPa over the EC-genesis center. However, the ascent motion driven by the adiabatic effect increases at both the upper and lower troposphere within the EC-genesis. The counterbalance of the above two effects leads to the stable pattern of the intensity of the EC-genesis. The dominant factor in EC-genesis has transferred from the diabatic effect to the adiabatic effect. Further investigation reveals the mechanism of the two effects from the circulation and moisture convergence and transport perspectives. The active circulation anomalies lead to stronger frontogenesis and enhance the adiabatic effects. The moisture outflows at the boundary and lower layers over East China weaken the diabatic effect.

Focusing on the forecasting and early warning of heavy precipitation in the key areas along the Sichuan-Xizang Railway,a heavy precipitation classification forecast model has been constructed for various subregions based on high spatiotemporal resolution Fengyun-4(FY-4)satellite data and ERA5 reanalysis product for the summers of 2020-2024,combined with the Light Gradient Boosting Machine algorithm.The model's interpretability is analyzed using Shapley additive explanation(SHAP),and the distribution characteristics of key forecasting factors are analyzed.Results show that the model achieves a critical success index(CSI)of 0.41 for heavy precipitation forecast in the key regions with a probability of detection(POD)reaching 0.76,and demonstrates a strong forecasting capability.Regional model analysis indicates that the POD for heavy precipitation is 0.83 and the CSI is 0.53 in western Sichuan.The POD is 0.69 and the CSI is 0.33 in the southeastern region of the Qingzang Plateau,indicating significant regional differences in the forecasting.SHAP and statistical analysis show that heavy precipitation in the southeastern Qingzang Plateau is mainly dominated by satellite brightness temperature difference(BTD)factors(such as BTD6.25-7.1 and BTD13.5-10.7)that reflect variations in mid-and upper-level water vapor and cloud top height,while thermal instability parameters(such as CAPE(convective available potential energy),K index)and low-level vertical motion are the main indicators for heavy precipitation in western Sichuan.60 min prior to the occurrence of heavy precipitation,key satellite parameters and physical parameters already exhibited statistically significant differences.Satellite parameters begin to show notable evolutionary characteristics as early as 150 min prior to the precipitation,providing quantitative reference for early warning.Based on interpretable machine learning methods,it is possible to not only enhance the objective forecasting ability of heavy precipitation,but also deepen the understanding of regional heavy precipitation mechanisms.This study provides scientific support for disaster prevention and reduction along the key areas of the Sichuan-Xizang Railway.

Abstract Ya'an is located in the transition zone between the eastern Tibetan Plateau and the Sichuan Basin (SB), featuring a distinct trumpet‐shaped terrain. This complex topography provides unique thermodynamic and dynamic conditions for convective initiation (CI), with highly intricate mechanisms. Based on radar observations, National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) analysis and forecast data, and high‐resolution simulations using the Weather Research and Forecasting (WRF) model, this study investigates the terrain‐related triggering mechanisms of a heavy rainfall event that occurred on the southwestern slope of Ya'an on 19 July 2024. Results indicate that convection was initiated over the southwestern slope between 19:00 and 20:00 BJT, with the initiation process jointly modulated by local thermal and dynamic effects. In the daytime, the northwestern slope exhibited a pronounced “heat‐pump” effect due to solar short‐wave radiative heating, enhancing the upslope flow. In the evening, downslope winds developed at the foot of the northwestern slope and extended toward the central SB. This thermally‐forced downslope flow acted to strengthen the dynamical blocking effect of the northwestern slope for the low‐level southeasterly flow from the southeastern SB, which was thus forced to turn leftward, forming barrier‐jet‐like northeasterly winds. In consequence, the upslope lifting on the southwestern slope was enhanced, thereby triggering the convection of the heavy rainfall event. This study elucidates the key mechanisms governing nocturnal CI in this complex terrain region, highlighting the importance of coupling between orographic thermal and dynamical processes.

The Yarlung Tsangpo Grand Canyon (YGC), a major moisture channel to the Tibetan Plateau, features a complex and poorly understood precipitation structure. This study pioneers the use of China's FengYun-3G Precipitation Measurement Radar (FY-3G PMR) to analyze the precipitation structure over the YGC during a plateau vortex event on 28 June 2024. Results reveal a dual-peak vertical structure with maxima at 2 km ASL and near the 5.5 km ASL 0 degrees C layer. Vortex development enhances ice production aloft, intensifying mixed-phase precipitation and warm-rain processes below. While stratiform precipitation dominates in frequency over the YGC, convective precipitation is 2-3 times more intense with a broader particle spectrum. Orographic lifting on northern slopes triggers intense convection with extreme precipitation rates (>10 mm hr(-1)). This study demonstrates FY-3G PMR's capability to resolve fine-scale precipitation structures over the plateau area, providing critical insights for further application of PMR over complex terrain.

Summer precipitation over the Qinghai–Xizang Plateau (QXP) exhibits an uneven east–west distribution. The zonal shear line (ZSL) over the QXP is the primary synoptic system influencing summer precipitation, and it is the only synoptic system that can largely span the QXP from east to west, having obvious implications for the distribution of summer precipitation over the QXP. The proximity of the zonal distribution of precipitation to the ZSL and the reasons for this unique proximity deserve an in-depth investigation. Based on the fifth generation ECMWF Reanalysis (ERA5) hourly data in 1980–2019, 11 ZSL cases that caused heavy precipitation over the QXP were composited, and horizontal atmospheric motion was decomposed into rotational and divergent components to diagnose the atmospheric dynamics responsible for the closeness of the precipitation and ZSL. The results demonstrate that obviously heavier precipitation lies in the eastern section of the ZSL (ZSLES, east of 88.5°E) than in the western section of the ZSL (ZSLWS, west of 88.5°E). At upper levels, both the anticyclonic circulation and divergent wind intensity are stronger in the ZSLES than in the ZSLWS, and a deeper convergence layer is present in the mid–lower troposphere of the ZSLES, resulting in upward air motion approximately twice the intensity of that in the ZSLWS. The net water vapor flux of the whole layer near the ZSLES is 7.7 times that near the ZSLWS, since water vapor is found to be transported mainly through the Yarlung Zangbo Grand Canyon and converge on the southern ZSLES. The stronger upward velocity lifts more water vapor near the ZSLES, resulting in notably greater precipitation than that observed in the ZSLWS.

Abstract The C vector, which is the extension of the Q vector in the three-dimensional space, restores the information of the ageostrophic motion lost by the latter. A comprehensive system has been established for the Q-vector diagnosis, but few studies have focused on the C vector. The vertical component of the C vector has dual physical interpretations: It describes both the rotation of the ageostrophic wind and the horizontal geopotential gradient. Based on the quasigeostrophic (QG) approximation and the vertical C-vector component in the p -coordinate system ( C p ), the C p tendency equation describing its local variations is derived. This equation has also dual physical interpretations, describing the local variation of both the ageostrophic vertical relative vorticity and the shape of the two-dimensional geopotential surface. The advection of C p , deformation, and the vorticity–divergence interactions determine the C p tendency. Based on the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA5) data and the objective cyclone identification method, the C p tendency equation is applied to diagnose the evolution of a Huang–Huai cyclone, which occurred during the extreme precipitation over Henan in July 2021. Compared with the commonly used vertical relative vorticity, C p has a better performance in both tracking the cyclone center and featuring its intensity variation. The results show that the C p tendency plays a major role in the evolution of the cyclone: Its distribution and variations drive the cyclone’s motion and predict that the cyclone will strengthen (decay), respectively. The deformation and the vorticity–divergence interactions collectively lead to the distributions and variations of the C p tendency, and the advection of C p can be neglected. Significance Statement The C vector is an improvement over the Q vector, with its vertical C-vector component ( C p ) depicting the barotropic dynamics of the ageostrophic motion that is lost by the Q vector. Nevertheless, few researchers have focused on the C vector. We developed the C-vector diagnosis by deriving the C p tendency equation. Theoretical discussions show that the equation contains complete information about the quasigeostrophic (QG) kinematics, and a case study proves its usefulness in describing the evolution of the synoptic-scale cyclone. This study can provide a new look at the application and development of the C-vector diagnosis.

The steep eastern slope of the Tibetan Plateau (ESTP) is a key area for the construction of the Sichuan-Tibet Railway. Understanding the diurnal variation of summer precipitation is essential for both construction and operational safety. Using hourly CLDAS-V2.0 precipitation data from the National Meteorological Information Center for 2016-2021, this study examines the diurnal characteristics of summer precipitation over the steep ESTP. In combination with circulation classification, the underlying causes of this diurnal variation are also investigated from the perspective of regional precipitation events (RPEs). Results reveal a pronounced unimodal diurnal variation of precipitation over the steep ESTP, with a marked east-west contrast across 102 degrees E in peak timing. The peak occurs near 18 local solar time (LST) in the western region (west of 102 degrees E), whereas it shifts to around 23 LST in the eastern region (east of 102 degrees E). The eastward RPEs, characterized by a west-east migration of the precipitation center, dominate the east-west peak-timing difference. Eastward RPEs can be further classified into two circulation types: a trough-dominated type (about 70%) and a western Pacific subtropical high type (about 30%). The east-west difference in precipitation peak timing arises from the temporal offset between moisture convergence and ascent, with anomalous ascent dominating under the trough regime and anomalous moisture convergence dominating under the subtropical high regime. These findings enhance understanding of diurnal precipitation over complex terrain and offer implications for hydrological risk assessment and railway planning.

The relationship between the Tibetan Plateau (TP) climate and the South Asian monsoon is a subject of extensive research. During July-August (JA), the TP zonal shear line (ZSL) is a key precipitation system in the atmospheric boundary layer over the TP. The TP ZSL frequency variability exhibits a pronounced anti-phase relationship in precipitation between the southeastern TP (SETP) and northwestern South Asia (Pakistan), with correlations of 0.75 over the TP and − 0.75 over Pakistan. Both observational and simulation results indicate that frequent ZSL occurrence over the central TP enhances low-level convergence along the ZSL. This promotes local precipitation and latent heat release, which subsequently induces a counterclockwise zonal-vertical circulation anomaly between the SETP and Pakistan. The circulation anomaly is characterized by ascending motion over the SETP, descending motion over Pakistan, with upper-tropospheric easterly outflow from the TP toward Pakistan and mid-to-lower tropospheric westerly moisture transport back to the TP. Such a mechanism favors precipitation over the SETP while suppressing it over Pakistan, which provides new insights into the impacts of the TP weather system on the South Asian monsoon precipitation.

The Eurasian continent, specifically Europe, West Asia, East Asia, and the Russian Far East, experienced anomalously high temperatures during the summer of 2022. The physical drivers of this unusually warm summer are investigated using the dominant empirical orthogonal function (EOF) modes of summer 2-m air temperature over Eurasia for the period 1960-2022. The results indicate that the exceptionally warm conditions were primarily linked to three climatic modes. The first mode, explaining 36.8% of the total variance, represents a background warming trend favouring elevated temperatures. The second mode, accounting for 12.3% of the variance, is closely related to the interannual variability of La Ni & ntilde;a conditions and a pronounced sea surface temperature gradient in the North Atlantic. These factors trigger mid-high-latitude wave trains and modulate the Hadley and Walker circulations, collectively fostering persistent anticyclonic anomalies. The third mode, explaining 11.1% of the variance, corresponds to the Pacific Decadal Oscillation (PDO), which triggers a circumglobal teleconnection pattern that guides wave energy to modulate Eurasian circulation. Diagnoses based on Rossby wave source analysis and wave activity flux further support the dynamical roles of these modes. [Traduit par la r & eacute;daction] Le continent eurasien, plus pr & eacute;cis & eacute;ment, l'Europe, l'Asie occidentale, l'Asie orientale et l'Extr & ecirc;me-Orient russe ont connu des temp & eacute;ratures anormalement & eacute;lev & eacute;es pendant l'& eacute;t & eacute; 2022. Les facteurs physiques & agrave; l'origine de cet & eacute;t & eacute; exceptionnellement chaud sont & eacute;tudi & eacute;s au moyen des modes empiriques orthogonaux (MEO) dominants de la temp & eacute;rature de l'air & agrave; 2 m au-dessus de l'Eurasie pour la p & eacute;riode 1960-2022. Les r & eacute;sultats indiquent que les conditions exceptionnellement chaudes & eacute;taient principalement li & eacute;es & agrave; trois modes climatiques. Le premier mode, qui explique 36,8 % de la variance totale, repr & eacute;sente une tendance g & eacute;n & eacute;rale au r & eacute;chauffement favorisant des temp & eacute;ratures & eacute;lev & eacute;es. Le deuxi & egrave;me mode, qui repr & eacute;sente 12,3 % de la variance, est & eacute;troitement li & eacute; & agrave; la variabilit & eacute; interannuelle des conditions La Ni & ntilde;a et & agrave; un gradient prononc & eacute; de la temp & eacute;rature de surface de la mer dans l'Atlantique Nord. Ces facteurs d & eacute;clenchent des trains d'ondes & agrave; moyenne et haute latitude et modulent les circulations de Hadley et de Walker, favorisant collectivement des anomalies anticycloniques persistantes. Le troisi & egrave;me mode, qui explique 11,1 % de la variance, correspond & agrave; l'oscillation d & eacute;cennale du Pacifique (ODP), qui d & eacute;clenche un sch & eacute;ma de t & eacute;l & eacute;connexion circumglobal qui guide l'& eacute;nergie des ondes pour moduler la circulation eurasienne. Les diagnostics bas & eacute;s sur l'analyse des sources d'ondes de Rossby et le flux d'activit & eacute; des ondes confirment encore davantage le r & ocirc;le dynamique de ces modes.

Heavy precipitation events have a greater impact on ecology, economy, and human livelihoods than general precipitation events. Based on observational data from 19 meteorological stations, two gridded daily precipitation datasets, and the ERA5 monthly reanalysis dataset from June to August during 1961-2022, this study investigates the inter-decadal variations of summer heavy precipitation and its underlying mechanisms in the Three-River Source (TRS) region, known as the water tower of China. The results show that over the past 60 years, summer heavy precipitation in the TRS has exhibited an overall increasing trend, with a significantly stronger trend in the eastern TRS (98 degrees-102 degrees E) than in its central and western parts. The interannual variation rate is relatively larger in the first three decades, but summer heavy precipitation in the latter 30 years initially decreases before increasing again. Since the 21st century, a Silk Road-like wave train characterized by positive-negative-positive geopotential height anomalies (anticyclone-cyclone-anticyclone) has dominated the middle and upper troposphere over Eastern Europe, Central Asia, and East Asia. During this period, the western Pacific subtropical high has intensified and extended westward, while the South Asian high has strengthened and extended eastward, creating a synoptic background that favours the interdecadal increase in summer heavy precipitation in the TRS. Since the 21st century, the westerly jet has intensified, shifted northward, and extended eastward, contributing to enhanced upper-level divergence and lower-level convergence over the TRS region located south of the jet core. Additionally, a notable rise in spring sensible heat (SH) around 2003 strengthened the thermal pumping effect over the TRS, which, combined with increased atmospheric instability, provided favourable thermodynamic lifting conditions for heavy precipitation events in the region since the 21st century. In addition, the inter-decadal variation of the regional net water vapour budget follows a similar pattern, showing a transition from less to more around 2002. The strengthened anticyclonic circulation in Northeast Asia has reduced the outflow of water vapour from the eastern boundary of the TRS. Meanwhile, intensified southwesterly water vapour transport and enhanced water vapour convergence have further contributed to the interdecadal increase in both summer heavy precipitation and the net water vapour budget in the TRS since the 21st century.

The convection over the Tibetan Plateau (TP) is active during the warm season, but the characteristics of the convective initiation (CI) remain less understood. Based on the observation data of FengYun-4A (FY-4A) satellite from 2018 to 2022, the temporal and spatial distribution characteristics of CI during the warm season over the TP have been investigated. It is found that the CI mainly occurs on the windward slopes of the valley plains along the mountain ranges in the warm season over the TP, with a high-frequency area located at 27 degrees N-30 degrees N, 87 degrees E-92 degrees E. CI occurrences are closely linked to monsoon activity, intensifying with the onset of the monsoon and exhibiting a northward expansion during summer. The CI presents a single diurnal peak at 13:00 (local solar time, the same below) and a minimum at 23:00. Daytime CI primarily occurs over the plains, whereas nighttime initiation is mainly concentrated along the hillsides. The study on the CI in the warm season over the TP is beneficial to deepening the understanding of the development of convection.

Tibetan Plateau vortices (TPVs) are the major precipitation‐producing weather system, which dominates the water supplies over the TP. Serial clustering is one of the basic features of TPVs and is closely related to the atmospheric intraseasonal oscillation of the TP. Through a database of TPVs derived from multiple reanalysis data sets, we investigated the spatiotemporal characteristics of TPV clustering (TPVC) and its connection with the atmospheric quasi‐biweekly oscillation (QBWO). The TPV tracks from variant reanalysis data sets reproduced consistent features for TPVC. The database revealed that the TPVC primarily occurs during the warm season and exhibits significant interannual variability. TPV clustering frequently occurs during the positive phase of the QBWO, in which the TP emerges cyclonic anomalies at lower atmospheric levels and anticyclonic anomalies at upper levels. This configuration creates a baroclinic structure that favors the formation of TPVCs. Conversely, the negative phase of QBWO results in an inverse atmospheric anomaly pattern, reducing TPVC occurrences. The interannual variability of TPVCs is primarily influenced by the amplitude of relative vorticity rather than the frequency of positive or negative phases. Furthermore, there are distinct differences in circulation patterns between years with high and low TPVC frequencies. In high‐TPVC (low‐TPVC) years, the lower levels of the TP predominantly show positive (negative) vorticity anomalies, accompanied by an anticyclone (cyclone) in the northern TP and a cyclone (anticyclone) in the eastern TP, while an anti‐cyclonic (cyclonic) anomaly is active over the TP that indicates an intensified (weakened) South Asian High.

The Tibetan Plateau (TP) zonal shear line (TPZSL) is one of the most typical precipitation-producing weather systems over the TP. In this paper, based on ERA-5 reanalysis data and observation data from June to August 1980-2019, TPZSLs are identified by objective identification technologies and then classified in detail. The spatiotemporal distributions and the dynamic and thermodynamic characteristics of TPZSLs are revealed in different subregions of northeast (NE), northwest (NW), southeast (SE) and southwest (SW) TP. Results show that an average of 93 TPZSLs generate each year with a striking diurnal variation: a preferential genesis during afternoon to night and a wee-hours dissipation peak. TPZSLs occur frequently in the range of 76 degrees similar to 103 degrees E, 29 degrees similar to 36 degrees N and are concentrated in the area of 76 degrees similar to 85 degrees E, 32 degrees similar to 35 degrees N in the central and western TP. TPZSLs are mainly oriented in the east-west direction (72.9%), and the majority of TPZSLs remain stationary (58.7%). The horizontal and vertical scales of TPZSLs vary significantly across subregions, with the largest horizontal scale in the SE and the deepest vertical scale in the SW. Except for the southwestern TPZSLs, TPZSLs incline northward with increasing altitude. All TPZSLs at 500 hPa are within areas of positive vorticity; notably, TPZSLs in NW are positioned north to the maximum vorticity centre, while the remaining TPZSLs intersect the centre. TPZSLs in NW, SW and SE are situated within convergence zones where convergence centres are situated at eastern and western ends of these shear lines. Vertically, TPZSLs in the NW and NE are embedded within ascending airflow. Except for those in the northeastern TP, all TPZSLs are located within the high-temperature and high-moisture areas. This research serves as an essential reference for comprehending the genesis and evolutionary processes of TPZSLs.

Using 30 years of NCEP/NCAR reanalysis data from winter (January), along with daily precipitation data from the China Meteorological Administration (CMA), this study employed an objective recognition method to classify southern branch troughs (SBTs) into eastern and western types. Subsequently, an analysis was conducted to identify the structural characteristics of each type and evaluate their effects on precipitation. The findings reveal that the eastern and western SBTs are located at different coordinates at 500 hPa, each affecting distinct precipitation zones. Specifically, the eastern SBT influences regions east of 90 degrees E, particularly Yunnan, while the western SBT primarily impacts areas west of 90 degrees E, with a pronounced effect on southern Tibet. Dynamic analysis indicates that both types of SBTs manifest as baroclinic troughs, though the western type exhibits stronger dynamic conditions than the eastern type. Both SBTs types are characterised by warm, moist advection ahead of the trough and cold, dry advection behind it. The eastern SBT shows more favourable thermal conditions than the western SBTs. Water vapour associated with both types of SBTs is concentrated at the front of the troughs below 450 hPa, with convergence observed below 700 hPa. Additionally, the eastern SBTs generate more pronounced water vapour convergence compared to the western SBT. Notably, torrential precipitation related to the eastern SBTs is driven by water vapour from the outer circulation of the western Pacific subtropical high, with additional moisture from the Bay of Bengal. In contrast, the water vapour associated with the western SBT primarily originates from the Arabian Sea and is supplemented by moisture from the Bay of Bengal.

The Huang-Huai River Basin (HHRB) in East China is highly susceptible to frequent floods and droughts, making it one of the most disaster-prone regions in China. Extratropical cyclones (ETCs) are the primary weather systems generating precipitation over the HHRB. This study investigates the spatiotemporal characteristics and precipitation patterns of ETCs affecting the HHRB, based on a long-term dataset (1979-2022) derived from ERA5 reanalysis. On average, 33.2 ETCs traverse the HHRB annually, exhibiting a statistically insignificant increasing trend over the study period. Most ETC activity occurs during summer months and nighttime hours. ETCs contribute to approximately 60% of the HHRB's total precipitation, with their contribution increasing for more intense precipitation events. Based on source regions and tracks, the ETCs are classified into five distinct types: locally generated systems and those originating from northwestern, northeastern, southwestern, and southern China. Locally generated ETCs produce the largest total precipitation, whereas those originating from southwestern China trigger the most intense rainfall events. ETC-induced precipitation plays a crucial role in driving summer floods and droughts over the HHRB. Consequently, a deeper understanding of the characteristics, formation mechanisms, and precipitation-generating processes of these systems is essential for effective disaster prevention and mitigation strategies.

Research on complete rainfall events rather than rainfall moments is more conducive to deepening the understanding of the laws of precipitation processes. Studying rainfall events over the Tibetan Plateau (TP) can fill some gaps in TP precipitation research and is particularly significant under global warming. This study investigated summer rainfall events over the TP during 2000-21 using GPM datasets by focusing on impact areas, evolutionary features, and regional variations. Furthermore, topographic influences on rainfall events were quantified, and possible causes across regions were explored. Results suggest that the mean duration of rainfall events is 4.2 h (up to 8.6 h), and the mean longest duration is 19 h (up to 89 h), with maxima occurring near the Yarlung Tsangpo Grand Canyon. Rainfall events can be categorized (LRE, 7-12 h), and ultra-LRE (ULRE, >12 h) based on duration. The longer the duration, the lower the frequency of rainfall events and the more southerly the impact area. The duration of rainfall events below 2000 m generally (about 90%) exceeds the TP average, highlighting elevation's influences on rainfall events. Rainfall event evolutionary characteristics vary by region and topography. In hillsides or plateaus (regions A and D), the precipitation peak mainly occurs in the afternoon. Conversely, in basins or valleys (regions B and C), the peak is concentrated at night. Differences in atmospheric dynamical and thermal conditions caused by TP topography are major factors for different rainfall events.

The Sanjiangyuan region, known as the “Water Tower of China”, is the source of the Yangtze, Yellow, and Lancang rivers. The diurnal variation of summer precipitation in this region is essential to the regional water cycle. In this study, we utilize the Tropical Rainfall Measuring Mission (TRMM) 3B42 Version 7 and the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) datasets to investigate the diurnal patterns of summer precipitation in the Sanjiangyuan region. Furthermore, we explore the underlying causes of these diurnal variations in precipitation from the perspective of moisture. The results show that: (1) the climatological summer precipitation in the Sanjiangyuan area follows a diurnal pattern, with less rainfall during the day and more at night, peaking at 20 Beijing Time Coordinate. (2) The diurnal variation in summer precipitation in the Sanjiangyuan area is mainly caused by the diurnal cycle of horizontal moisture transport, with precipitation peaking when moisture transport is at its maximum. (3) The diurnal variation in horizontal moisture transport in the Sanjiangyuan area is closely linked to the moisture balance at the region’s eastern and northern boundaries. Boundary layer inertial oscillations primarily govern the diurnal moisture budgets along the eastern boundary, while mountain-valley wind circulations predominantly control them along the northern boundary.

As a critical component of global water cycle, diurnal variation of precipitation (DVP) exhibits significant spatial heterogeneity under topographic effect. However, DVP's dependency on elevation and evolution in a warming climate remain unclear. This study investigates the elevation‐dependency of the terrestrial DVP in boreal summer and its evolution using 20‐year satellite data. Results show that late‐afternoon to evening is the major peak period for boreal summer precipitation across all altitudes, while late night is the secondary peak period at 2–4 km above sea level (ASL). Precipitation tends to peak more in the late afternoon above 5 km ASL compared to lower altitudes. With global warming, the late‐afternoon peak is weakening while the evening peak is strengthening, particularly above 4 km ASL. Diurnal precipitation may have become more homogeneous with narrowing amplitude, which is more pronounced at lower elevations. These findings highlight DVP is elevation‐dependent and is evolving in probable response to global warming.