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A Lagrangian model—the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT)—is used to quantify changes in moisture sources and paths for precipitation over North China's Henan Province associated with tropical cyclone (TC) over the western North Pacific (WNP) during July–August of 1979–2021. During TC-active periods, an anomalous cyclone over the WNP enhances southeasterly and reduces southwesterly moisture transport to Henan. Accordingly, compared to TC-inactive periods, moisture contributions from the Pacific Ocean (PO), eastern China (EC), and the local area (Local) are significantly enhanced by 48.32% (16.73% versus 11.28%), 20.42% (9.44% versus 7.84%), and 2.89% (4.91% versus 4.77%), respectively, while moisture contributions from the Indian Ocean (IO), Southwestern China (SWC), Eurasia (EA), and the South China Sea (SCS) are significantly reduced by −31.90% (8.61% versus 12.64%), −16.27% (4.60% versus 5.50%), −8.81% (19.10% versus 20.95%), and −6.92% (12.18% versus 13.09%). Furthermore, the moisture transport for a catastrophic extreme rainfall event during 17–22 July ("21⋅7" event) influenced by Typhoon Infa is investigated. Compared to the mean state during TC-active periods, the moisture contribution from the PO was substantially increased by 126.32% (37.87% versus 16.73%), while that from IO significantly decreased by −98.26% (0.15% versus 8.61%) during the "21⋅7" event. Analyses with a bootstrap resampling method show that moisture contributions from the PO fall outside the +6σ range, for both the TC-active and TC-inactive probability distributions. Thus, the "21⋅7" event is rare and extreme in terms of the moisture contribution from the PO, with the occurrence probability being less than 1 in 1 million times. Significance Statement: Henan, one of the most populated provinces in China, experienced a catastrophic extreme precipitation event in July 2021 (the "21⋅7" event), coinciding with the activity of a tropical cyclone (TC) over the western North Pacific, which helps establish the moisture channel. Using a Lagrangian model, we provide a better understanding of how moisture transport changes associated with TC for the mean state of 1979–2021, and reveal how extreme is the moisture transport for the "21⋅7" event with the bootstrap technique. It is found that during active TC periods, the moisture contribution from the Pacific Ocean (the Indian Ocean) is significantly enhanced (reduced). For every 1 000 000 six-day events, less than one instance like the "21⋅7" event should be expected. [ABSTRACT FROM AUTHOR]

This study investigates future changes in daily precipitation extremes and the involved physics over the global land monsoon (GM) region using climate models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). The daily precipitation extreme is identified by the cutoff scale, measuring the extreme tail of the precipitation distribution. Compared to the historical period, multimodel results reveal a continuous increase in precipitation extremes under four scenarios, with a progressively higher fraction of precipitation exceeding the historical cutoff scale when moving into the future. The rise of the cutoff scale by the end of the century is reduced by 57.8% in the moderate emission scenario relative to the highest scenario, underscoring the social benefit in reducing emissions. The cutoff scale sensitivity, defined by the increasing rates of the cutoff scale over the GM region to the global mean surface temperature increase, is nearly independent of the projected periods and emission scenarios, roughly 8.0% K−1 by averaging all periods and scenarios. To understand the cause of the changes, we applied a physical scaling diagnostic to decompose them into thermodynamic and dynamic contributions. We find that thermodynamics and dynamics have comparable contributions to the intensified precipitation extremes in the GM region. Changes in thermodynamic scaling contribute to a spatially uniform increase pattern, while changes in dynamic scaling dominate the regional differences in the increased precipitation extremes. Furthermore, the large intermodel spread of the projection is primarily attributed to variations of dynamic scaling among models. [ABSTRACT FROM AUTHOR]

Precipitation accumulations, integrated over rainfall events, are investigated using hourly data across continental China during the warm season (May–October) from 1980 to 2015. Physically, the probability of precipitation accumulations drops slowly with event size up to an approximately exponential cutoff scale sL where probability drops much faster. Hence sL can be used as an indicator of high accumulation percentiles (i.e., extreme precipitation accumulations). Overall, the climatology of sL over continental China is about 54 mm. In terms of cutoff changes, the current warming stage (1980–2015) is divided into two periods, 1980–97 and 1998–2015. We find that the cutoff in 1998–2015 increases about 5.6% compared with that of 1980–97, with an average station increase of 4.7%. Regionally, sL increases are observed over East China (10.9% ± 1.5%), Northwest China (9.7% ± 2.5%), South China (9.4% ± 1.4%), southern Southwest China (5.6% ± 1.2%), and Central China (5.3% ± 1.0%), with decreases over North China (−10.3% ± 1.3%), Northeast China (−4.9% ± 1.5%), and northern Southwest China (−3.9% ± 1.8%). The conditional risk ratios for five subregions with increased cutoff sL are all greater than 1.0, indicating an increased risk of large precipitation accumulations in the most recent period. For high precipitation accumulations larger than the 99th percentile of accumulation s99, the risk of extreme precipitation over these regions can increase above 20% except for South China. These increases of extreme accumulations can be largely explained by the extended duration of extreme accumulation events, especially for "extremely extreme" precipitation greater than s99. [ABSTRACT FROM AUTHOR]

Correlations of the urban heat island intensity (UHII) and key surface variables with the short-duration intense rainfall (SDIR) events are examined for the Beijing urban areas by applying hourly data of a high-density automatic weather station (AWS) network. Higher frequencies (amounts) of the SDIR events are found in or near the central urban area, and most of the SDIR events begin to appear in late evening and nighttime, but tend to end in late night and early morning. Correlations of the UHII with the SDIR frequency (amount) are all highly significant for more than 3 h ahead of the beginning of the SDIR events. Although the UHII at immediate hours (<3 h) before the SDIR occurrence is more indicative of SDIR events, their occurrence more depends on the magnitude of the UHII at earlier hours. The UHII before the beginning of the SDIR events also shows high-value centers in the central urban area, which is generally consistent with the distribution of the SDIR events. The spatial and temporal patterns of regional SDIR events exhibit similar characteristics to the site-based SDIR events and also show a good relationship with the UHII in the urban areas. In addition to the UHII over the urban areas, surface air temperature, surface air pressure, relative humidity, and near-surface wind directions at the Beijing station experience large changes before and after the beginning time of regional SDIR events, and have the potential to indicate the occurrence of SDIR events in the studied area. [ABSTRACT FROM AUTHOR]