Frequent extreme precipitation events have resulted in severe disasters to agriculture, the economy, and human health in recent decades. Widespread concerns about extreme precipitation have been aroused among the public, the government, and the research community. Researchers have conducted numerous studies on the mechanisms responsible for extreme precipitation events (Agel et al., 2018;Collow et al., 2016). Favorable local dynamic conditions (ascending motion) and instability are critical for the occurrence of extreme precipitation. Abundant moisture supply is another indispensable condition for extreme precipitation.In recent years, many studies have focused on moisture transport and sources for precipitation, including precipitation extremes. Two main approaches are widely used in studies on moisture transport. One is in the Eulerian view by calculating water vapor transport or by identifying and tracking the variation in atmospheric rivers (Sun & Wang, 2013;Tan et al., 2021). A deficiency of the Eulerian view is that it can neither track moisture from the sources to the precipitation area nor track moisture from the target region back to its sources. The other is in the Lagrangian view by tracking the moisture of particles (or air parcels) forward or backward using Lagrangian trajectory models (Sodemann et al., 2008;Sodemann & Zubler, 2010). The Lagrangian model can provide moisture variation processes from evaporation to precipitation along the transport trajectories. Several Lagrangian trajectory models are available, such as the Lagrangian particle dispersion model FLEXPART (
This study analyzes the synoptic‐scale circulation patterns favorable for regional extreme precipitation events over southwest China (SWC) from 1979 to 2018 occurring during the rainy seasons. The whole SWC is regionalized into two subregions, western SWC and eastern SWC, according to the spatial distribution of two extreme precipitation indices. Furthermore, the atmospheric patterns associated with the independent regional extreme precipitation events (REPEs) that occurred over the two subregions are categorized into two types using k‐means clustering. For type 1, a Rossby wave train originating from the Northeast Atlantic almost a week before REPEs leads to an anomalous low over the eastern Tibetan Plateau (TP), inducing upper‐troposphere divergence and ascending motion over SWC. Moreover, anomalous convective activities over India and the Bay of Bengal (the enhanced and westward‐extended western Pacific subtropical high) are critical precursors of REPEs over western (eastern) SWC. For type 2, an anomalous high is developed over the Ural Mountains at least a week prior to REPEs. The subsequent anomalous low over Lake Baikal and eastward‐shifted South Asian high are conducive to forming updrafts over SWC. An anomalous anticyclone at the middle‐to‐lower troposphere south of the TP is the main moisture contributor. Discrepancies in the zonal location of the Lake Baikal low and the strength of the Ural Mountain high, as well as the intensity of atmospheric circulation anomalies at low latitudes, are the major differences between the type 2 events occurring in western and eastern SWC.
The interannual variability in summer precipitation intraseasonal oscillation intensity over southwest China (SWC) is investigated in this study. The results indicate that the 7–20-day period dominates the intraseasonal variability in summer SWC precipitation. The leading mode of summer SWC precipitation 7–20-day oscillation intensity (SPOI) is a north-south dipole pattern with prominent interannual variability. The atmospheric circulation anomalies from both tropics and mid-high latitudes are responsible for the interannual variability in the dipole pattern. In the tropics, an enhanced local Hadley cell and an anomalous anticyclone over southern China and the Northwest Pacific contribute to the north-positive-south-negative pattern of SPOI by inducing moisture convergence/divergence over northern/southern SWC in the background state. In the mid-high latitudes, the 7–20-day Rossby wave trains along the subtropical jet are crucial for the 7–20-day precipitation over northern SWC. Further analyses suggest that the sea surface temperature (SST) anomalies over the Maritime Continent (MC) and the North Atlantic (NA) are associated with the SPOI dipole pattern. The MC SST warming causes convection anomalies over the tropical Indo-Pacific, consequently triggering a Matsuno-Gill-type atmospheric response conducive to the north-positive-south-negative pattern of SPOI. The NA SST tripole triggers a Rossby wave train across Eurasia that strengthens the East Asian westerly jet and enhances 7–20-day atmospheric variability, consequently favoring the variability of 7–20-day precipitation over northern SWC. Diagnoses of moisture and vorticity budgets further indicate the importance of the interaction between intraseasonal fluctuations and atmospheric background in the formation of the north-south difference in 7–20-day precipitation variability over SWC.
The evaluation of gridded high-resolution precipitation products (HRPPs) is important in areas with complex topography, because rain gauges that are unevenly and sparsely distributed over an area cannot effectively reflect the spatial variabilities of the precipitation and related extremes in detail. In this study, the applicability of six satellite-based precipitation products (TMPA-3B42V7, IMERG, GSMaP-Gauge, CMORPH-CRT, PERSIANN-CDR and GPCP) and five gauge-based precipitation products (APHRODITE, CN05.1, GPCC-D, GPCC-M and CRU) over Southwest China (SWC) from 1998 to 2016 is evaluated by performing a comparison with meteorological station observations. The results show that GPCC-M exhibits the best performances for annual, seasonal and monthly precipitation, which is supported by the lowest root mean square errors (RMSEs) for annual and seasonal precipitation and the lowest normalized root mean square error (NRMSE) for monthly precipitation. According to the NRMSE and critical success index (CSI), CN05.1 outperforms the other HRPPs at detecting daily precipitation; however, CN05.1 tends to overestimate the frequencies of light precipitation and underestimate the frequencies of heavy precipitation, which is reflected by the probability density function (PDF) for daily precipitation. The bias ratio (BIAS) and extreme precipitation indices show that IMERG shows numerous advantages over the other HRPPs in detecting extreme precipitation and estimating the precipitation intensity. Such results are helpful for future research on precipitation/extremes and related hydrometeorological disasters that occur throughout Southwest China.
Spring extreme precipitation (SEP) significantly disturbs spring ploughing over Southwest China (SWC), bringing challenges for agricultural activities and production over the region. This study investigates the interannual relationship between SWC SEP and sea surface temperature (SST) in preceding winter, from a perspective of prediction. It is found that the dominate mode of SWC SEP interannual variability mainly reflects the variability over the eastern part. The variability of eastern SWC SEP has an enhanced connection with a dipole SST pattern over the South Indian Ocean in preceding winter after the late 1980s. Under the warmer SST background after the late 1980s, the South Indian Ocean dipole SST pattern can lead to significant convection activity over tropical central and western Indian Ocean. The tropical diabatic heating associated with enhanced convection can strengthen the western North Pacific anticyclone, which transports more water vapour to eastern SWC and induces stronger moisture convergence there, providing favourable moisture condition for the SEP occurrence. In addition, the dipole SST pattern can strengthen upward motion over eastern SWC through exiting a meridional circulation, providing a favourable dynamic condition for the SEP occurrence over there.In contrast, under the colder SST background before the late 1980s, the dipole SST pattern-related convection and atmospheric circulation anomalies are weak over the Indo-Pacific region. Therefore, the relationship of the dipole SST pattern with SEP over eastern SWC is weak before the late 1980s. The SST signals with one-season leading could provide valuable source for seasonal prediction of eastern SWC SEP variability after the late 1980s.
A wet-to-dry shift in summer over the Sichuan Basin (SCB) during the late 20th century was noticed by previous studies. However, this study found that summer precipitation over SCB significantly increases during the past two decades, with an abrupt change point around 2011/2012. An anomalous
<p>Southwest China (SWC) is vulnerable to disasters caused by extreme precipitation. This study investigates the mechanisms of low-latitude intraseasonal oscillations affecting regional persistent extreme precipitation events (RPEPEs) over SWC during rainy seasons. Most of the RPEPEs over SWC are dominated by 7&#8211;20-day variability. The RPEPEs over SWC are preconditioned by two different types of 7&#8211;20-day Rossby waves with almost opposite phases over the western North Pacific (WNP). The two types of 7&#8211;20-day Rossby waves have direct (indirect) effects on Type 1 (2) RPEPEs, respectively. For Type 1, a coupled 7&#8211;20-day low-level anticyclone and suppressed convection originating from the tropical WNP propagate northwestward and cover the region from the South China Sea (SCS) to the Bay of Bengal before the RPEPEs. The anticyclone triggers ascending motion over SWC and transports more moisture to SWC, favoring the SWC RPEPEs. Before the Type 2 RPEPEs, a coupled 7&#8211;20-day low-level cyclone and enhanced convection propagates from the tropical WNP to the SCS. The enhanced convection over the SCS leads to the westward extension of the western Pacific subtropical high (WPSH) and the eastward shift of the South Asian high (SAH). The variations in the WPSH and the SAH directly cause SWC RPEPEs by inducing ascending motion and transporting moisture. The mechanisms for Type 2 RPEPEs tend to work under the background with a strong WPSH. Using a Lagrangian model, we found that both the 7&#8211;20-day oscillations and their background atmospheric circulations result in significant differences in moisture sources for the two types of RPEPEs. These findings benefit a better understanding of SWC extreme precipitation events.</p>
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