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Influence of changes in extreme daily rainfall distribution on the stability of residual soil slopes

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Big Earth Data 2023年第1期7卷 101-125页

作者： Thapthai Chaithong Department of Geography Faculty of Social SciencesKasetsart UniversityBangkokThailand

Many landslides triggered by intense rainfall have occurred in moun-tainous areas in Thailand,causing major economic losses and infra-structure damage.extreme daily rainfall is a significant trigger for hillslope instability.Increases in extreme daily rainfall intensity due to climate change may be one of the key factors responsible for the increased landslides.Thus,in this context,changes in the intensity of extreme daily rainfall in Chiang Mai Province in North Thailand and their effects on hillslope stability are analyzed.Extreme rainfall is modeled using a generalized extreme value distribution and esti-mated for various return periods.A numerical analysis of seepage and an infinite slope stability model are combined to understand the hillslope response under Extreme rainfall conditions.The analysis period is divided into two periods of 34 years:1952 to 1985 and 1986 to 2019.According to the analysis results,the distribution of extreme daily rainfall changes in terms of location.The average annual daily maximum rainfall increased by approximately 11.13%.The maximum decrease in the safety factor is approximately 4.5%;therefore,these changes in extreme daily rainfall should be consid-ered in future landslide prevention policies.

关键词： Extreme rainfall generalized extreme value distribution slope stability landslide pore water pressure climate change residual soil

Predictability and skill of convection-permitting ensemble forecast systems in predicting the record-breaking“21·7”Extreme rainfall event in Henan Province,China

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Science China Earth Sciences 2022年第10期65卷 1879-1902页

作者： Kefeng ZHU Chenyue ZHANG Ming XUE Nan YANG Key Laboratory of Transportation Meteorology of China Meteorological Administration Nanjing Joint Institute for Atmospheric SciencesNanjing 210041China Key Laboratory of Mesoscale Severe Weather/Ministry of Education and School of Atmospheric Sciences Nanjing UniversityNanjing 210093China Center for Analysis and Prediction of Storms and School of Meteorology University of Oklahoma Norman Oklahoma 73072USA

During 19–21 July 2021,an Extreme rainfall event occurred in Henan Province,China,during which a recordbreaking maximum hourly rainfall of 201.9 mm was recorded in Zhengzhou at 09 UTC July 20.In this study,the predictability of this Extreme rainfall event is investigated using two convection-permitting ensemble forecast systems(CEFSs):one initialized from NCEP GEFS(named CEFS_GEFS)and the other initialized from time-lagged ERA5 data(named CEFS_ERA).Both are able to reproduce the daily heavy rainfall along the Taihang Mountains,but most members have significant position biases for the Extreme rainfall in Zhengzhou.For the hourly rainfall,a few members are able to capture the evolution and propagation of Extreme rainfall.However,all ensemble members underestimate the extreme hourly rainfall and have position errors of a few tens to a few hundreds of kilometers.Such results suggest that the predictability of the extreme hourly rainfall at the accuracy of city scale in Zhengzhou is low,especially by deterministic forecasting models,and the occurrence of the extreme requires many favorable conditions to happen simultaneously.In terms of the Brier score,CEFS_GEFS performs better than CEFS_ERA.The latter lacks spread,especially in regions with scarce rain,resulting in less dispersion in precipitation distributions and larger probability forecast error.When a neighborhood is applied,the probability of precipitation(POP)is significantly increased over Zhengzhou.While the traditional POP shows almost no skill for hourly rainfall≥25 mm h-1,the neighborhood POP significantly improves the forecast skill score,for both daily and hourly rainfall,suggesting higher predictability when spatial error among the ensemble members is allowed.

关键词： Convective-permitting ensemble forecasts Neighborhood precipitation probability Extreme rainfall

On the Influences of Urbanization on the Extreme rainfall over Zhengzhou on 20 July 2021: A Convection-Permitting Ensemble Modeling Study

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Advances in Atmospheric Sciences 2023年第3期40卷 393-409页

作者： Yali LUO Jiahua ZHANG Miao YU Xudong LIANG Rudi XIA Yanyu GAO Xiaoyu GAO Jinfang YIN State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081China Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science and TechnologyNanjing 210044China School of Atmospheric Sciences Chengdu University of Information TechnologyChengdu 610225China

This study investigates the influences of urban land cover on the Extreme rainfall event over the Zhengzhou city in central China on 20 July 2021 using the Weather Research and Forecasting model at a convection-permitting scale[1-km resolution in the innermost domain(d3)].Two ensembles of simulation(CTRL,NURB),each consisting of 11 members with a multi-layer urban canopy model and various combinations of physics schemes,were conducted using different land cover scenarios:(i)the real urban land cover,(ii)all cities in d3 being replaced with natural land cover.The results suggest that CTRL reasonably reproduces the spatiotemporal evolution of rainstorms and the 24-h rainfall accumulation over the key region,although the maximum hourly rainfall is underestimated and displaced to the west or southwest by most members.The ensemble mean 24-h rainfall accumulation over the key region of heavy rainfall is reduced by 13%,and the maximum hourly rainfall simulated by each member is reduced by 15–70 mm in CTRL relative to NURB.The reduction in the simulated rainfall by urbanization is closely associated with numerous cities/towns to the south,southeast,and east of Zhengzhou.Their heating effects jointly lead to formation of anomalous upward motions in and above the planetary boundary layer(PBL),which exaggerates the PBL drying effect due to reduced evapotranspiration and also enhances the wind stilling effect due to increased surface friction in urban areas.As a result,the lateral inflows of moisture and high-θe(equivalent potential temperature)air from south and east to Zhengzhou are reduced.

关键词： urbanization Extreme rainfall convection-permitting ensemble simulation land-atmosphere interaction boundary layer water vapor transport

Contrasts between the Interannual Variations of Extreme rainfall over Western and Eastern Sichuan in Mid-summer

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Advances in Atmospheric Sciences 2022年第6期39卷 999-1011页

作者： Mengyu DENG Riyu LU Chaofan LI State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China Center for Monsoon System Research Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China College of Earth and Planetary Sciences University of the Chinese Academy of SciencesBeijing 100049China Institute of Plateau Meteorology China Meteorological Administration(CMA)Chengdu 610072China Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province Chengdu 610072China

rainfall amount in mid-summer(July and August)is much greater over eastern than western Sichuan,which are characterized by basin and plateau,respectively.It is shown that the interannual variations of Extreme rainfall over these two regions are roughly independent,and they correspond to distinct anomalies of both large-scale circulation and sea surface temperature(SST).The enhanced Extreme rainfall over western Sichuan is associated with a southward shift of the Asian westerly jet,while the enhanced Extreme rainfall over eastern Sichuan is associated with an anticyclonic anomaly in the upper troposphere over China.At low levels,on the other hand,the enhanced Extreme rainfall over western Sichuan is related to two components of wind anomalies,namely southwesterly over southwestern Sichuan and northeasterly over northeastern Sichuan,which favor more rainfall under the effects of the topography.Relatively speaking,the enhanced Extreme rainfall over eastern Sichuan corresponds to the low-level southerly anomalies to the east of Sichuan,which curve into northeasterly anomalies over the basin when they encounter the mountains to the north of the basin.Therefore,it can be concluded that the topography in and around Sichuan plays a crucial role in inducing Extreme rainfall both over western and eastern Sichuan.Finally,the enhanced Extreme rainfall in western and eastern Sichuan is related to warmer SSTs in the Maritime Continent and cooler SSTs in the equatorial central Pacific,respectively.

关键词： Extreme rainfall Sichuan interannual variation topography large-scale circulation

Climatology of Tropical Cyclone Extreme rainfall over China from 1960 to 2019

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Advances in Atmospheric Sciences 2022年第2期39卷 320-332页

作者： Ying LI Dajun ZHAO National Climate Centre Beijing 100081China State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesBeijing 100081China

Tropical cyclone Extreme rainfall(TCER)causes devastating floods and severe damage in China and it is therefore important to determine its long-term climatological distribution for both disaster prevention and operational forecasting.Based on the tropical cyclone(TC)best-track dataset and TC precipitation data from 1960 to 2019,the spatiotemporal distribution of TCER affecting China is analyzed.Results show that there were large regional differences in the threshold for TCER in China,decreasing from the southeastern coast to the northwest inland.TCER occurred infrequently in northern China but had a high intensity and was highly localized.The frequency and intensity of TCER showed slightly increasing trends over time and was most likely to occur in August(41.0%).Most of the TC precipitation processes with Extreme rainfall lasted for four to six days,with TCER mainly occurring on the third to fourth days.TCER with wide areas showed a northwestward prevailing track and a westward prevailing track.Strong TCs are not always accompanied by extreme precipitation while some weak TCs can lead to very Extreme rainfall.A total of 64.7%(35.3%)of the TCER samples occurred when the TC was centered over the land(sea).TCER≥250 mm was located within 3°of the center of the TC.When the center of the TC was located over the sea(land),the Extreme rainfall over land was most likely to appear on its northwestern(northeastern)side with a dispersed(concentrated)distribution.TCER has unique climatic characteristics relative to the TC precipitation.

关键词： tropical cyclones Extreme rainfall threshold track characteristics intensity characteristics

PV Perspective of Impacts on Downstream Extreme rainfall Event of a Tibetan Plateau Vortex Collaborating with a Southwest China Vortex

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Advances in Atmospheric Sciences 2021年第11期38卷 1835-1851页

作者： Guanshun ZHANG Jiangyu MAO Yimin LIU Guoxiong WU State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG) Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing 100029China University of Chinese Academy of Sciences Beijing 100049China

An Extreme rainfall event occurred over the middle and lower reaches of the Yangtze Basin(MLY)during the end of June 2016,which was attributable to a Tibetan Plateau(TP)Vortex(TPV)in conjunction with a Southwest China Vortex(SWCV).The physical mechanism for this event was investigated from Potential Vorticity(PV)and omega perspectives based on MERRA-2 reanalysis data.The cyclogenesis of the TPV over the northwestern TP along with the lower-tropospheric SWCV was found to involve a midtropospheric large-scale flow reconfiguration across western and eastern China with the formation of a high-amplitude Rossby wave.Subsequently,the eastward-moving TPV coalesced vertically with the SWCV over the eastern Sichuan Basin due to the positive vertical gradient of the TPV-related PV advection,leading the lower-tropospheric jet associated with moisture transport to intensify greatly and converge over the downstream MLY.The merged TPV−SWCV specially facilitated the upper-tropospheric isentropic-gliding ascending motion over the MLY.With the TPV-embedded mid-tropospheric trough migrating continuously eastward,the almost stagnant SWCV was re-separated from the overlying TPV,forming a more eastward-tilted high-PV configuration to trigger stronger ascending motion including isentropic-gliding,isentropic-displacement,and diabatic heating-related ascending components over the MLY.This led to more intense rainfall.Quantitative PV diagnoses demonstrate that both the coalescence and subsequent re-separation processes of the TPV with the SWCV were largely dominated by horizontal PV advection and PV generation due to vertically nonuniform diabatic heating,as well as the feedback of condensation latent heating on the isentropic-displacement vertical velocity.

关键词： Extreme rainfall Tibetan Plateau vortex Southwest China vortex PV vertical velocity

A Possible Dynamic Mechanism for Rapid Production of the extreme Hourly rainfall in Zhengzhou City on 20 July 2021

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Journal of Meteorological Research 2022年第1期36卷 6-25页

作者： Jinfang YIN Haodong GU Xudong LIANG Miao YU Jisong SUN Yanxin XIE Feng LI Chong WU State Key Laboratory of Severe Weather Chinese Academy of Meteorological SciencesChina Meteorological AdministrationBeijing 100081 Research Center for Disastrous Weather over Hengduan Mountains&Low-Latitude Plateau China Meteorological AdministrationKunming 650034

In this study,the unprecedented Extreme rainfall event during 19-20 July 2021,which caused devastating flooding in Zhengzhou City and its nearby areas,is examined based on observational data analysis and WRF model 40-h simulations on 1-km horizontal resolution.The results show that the model successfully reproduces(i)major synopticscale weather systems(i.e.,the western Pacific subtropical high,the Tibetan high,two typhoons,and the Huang-Huai cyclone),(ii)convective initiation along the east to north edge of the Songshan Mountain,where orographic lifting is obvious,and(iii)subsequent formation of the convective storm producing the Extreme rainfall in Zhengzhou.In particular,the model generates the maximum rainfall rate of 233 mm h^(-1)and 40-h accumulated rainfall of 704 mm,corresponding well to the observed extreme values of 201.9 mm h^(-1)and 818 mm,at nearly observed timing and location.Importantly,the model reproduces an intense quasi-stationary,well-organized meso-γ-scale convective system,surrounded by an arc-shaped convergence zone,allowing the development of convective updrafts in a three-quarter circle around the convective system,in a way similar to“multidirectional pumping,”attracting all associated precipitation overlaid and concentrated into the same trailing region to generate the extreme hourly rainfall over Zhengzhou.Our study emphasizes the significant contribution of the unique dynamic structure of the well-organized meso-γ-scale convective system to the record-high hourly rainfall.A possible dynamic mechanism for short-time Extreme rainfall production is proposed.That is,the arc-shaped convergence zone of the mesoscale convective system,acting like multidirectional lifting pumps,transports precipitation from different directions into the same region,and thus produces the Extreme rainfall.The results gained herein may shed new light on better understanding and forecasting of short-time Extreme rainfall.

关键词： Extreme rainfall meso-γ-scale convective system extreme hourly rainfall rate devastating flooding

Why Does Extreme rainfall Occur in Central China during the Summer of 2020 after a Weak El Niño?

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Advances in Atmospheric Sciences 2021年第12期38卷 2067-2081页

作者： Congxi FANG Yu LIU Qiufang CAI Huiming SONG The State Key Laboratory of Loess and Quaternary Geology Institute of Earth EnvironmentChinese Academy of SciencesXi’an710061China CAS Center for Excellence in Quaternary Science and Global Change Chinese Academy of SciencesXi’an710061China Laboratory for Ocean Dynamics and Climate Pilot Qingdao National Laboratory for Marine Science and TechnologyQingdao266000China

In summer 2020,Extreme rainfall occurred throughout the Yangtze River basin,Huaihe River basin,and southern Yellow River basin,which are defined here as the central China(CC)region.However,only a weak central Pacific(CP)El Niño happened during winter 2019/20,so the correlations between the El Niño–Southern Oscillation(ENSO)indices and ENSO-induced circulation anomalies were insufficient to explain this extreme precipitation event.In this study,reanalysis data and numerical experiments are employed to identify and verify the primary ENSO-related factors that cause this Extreme rainfall event.During summer 2020,unusually strong anomalous southwesterlies on the northwest side of an extremely strong Northwest Pacific anticyclone anomaly(NWPAC)contributed excess moisture and convective instability to the CC region,and thus,triggered extreme precipitation in this area.The tropical Indian Ocean(TIO)has warmed in recent decades,and consequently,intensified TIO basinwide warming appears after a weak El Niño,which excites an extremely strong NWPAC via the pathway of the Indo-western Pacific Ocean capacitor(IPOC)effect.Additionally,the ENSO event of 2019/20 should be treated as a fast-decaying CP El Niño rather than a general CP El Niño,so that the circulation and precipitation anomalies in summer 2020 can be better understood.Last,the increasing trend of tropospheric temperature and moisture content in the CC region after 2000 is also conducive to producing heavy precipitation.

关键词： Extreme rainfall Northwest Pacific anticyclone anomaly(NWPAC) Indo-western Pacific Ocean capacitor(IPOC) Tropical Indian Ocean warming trend fast-decaying El Niño

High-resolution Simulation of an extreme Heavy rainfall Event in Shanghai Using the Weather Research and Forecasting Model: Sensitivity to Planetary Boundary Layer Parameterization

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Advances in Atmospheric Sciences 2021年第1期38卷 98-115页

作者： Rui WANG Yiting ZHU Fengxue QIAO Xin-Zhong LIANG Han ZHANG Yang DING Key Laboratory of Geographic Information Science Ministry of EducationEast China Normal UniversityShanghai 200241China School of Geographic Sciences East China Normal UniversityShanghai 200241China Institute of Eco-Chongming Shanghai 200062China College of Atmospheric Science Nanjing University of Information Science and TechnologyNanjing 210044China Department of Atmospheric&Oceanic Science University of MarylandCollege ParkMaryland 20742USA Earth System Science Interdisciplinary Center University of MarylandCollege ParkMaryland 20742USA Shanghai Central Meteorological Observatory Shanghai 200030China

In this study,an Extreme rainfall event that occurred on 25 May 2018 over Shanghai and its nearby area was simulated using the Weather Research and Forecasting model,with a focus on the effects of planetary boundary layer(PBL)physics using double nesting with large grid ratios(15:1 and 9:1).The sensitivity of the precipitation forecast was examined through three PBL schemes:the Yonsei University Scheme,the Mellor−Yamada−Nakanishi Niino Level 2.5(MYNN)scheme,and the Mellor−Yamada−Janjic scheme.The PBL effects on boundary layer structures,convective thermodynamic and large-scale forcings were investigated to explain the model differences in Extreme rainfall distributions and hourly variations.The results indicated that in single coarser grids(15 km and 9 km),the Extreme rainfall amount was largely underestimated with all three PBL schemes.In the inner 1-km grid,the underestimated intensity was improved;however,using the MYNN scheme for the 1-km grid domain with explicitly resolved convection and nested within the 9-km grid using the Kain−Fritsch cumulus scheme,significant advantages over the other PBL schemes are revealed in predicting the Extreme rainfall distribution and the time of primary peak rainfall.MYNN,with the weakest vertical mixing,produced the shallowest and most humid inversion layer with the lowest lifting condensation level,but stronger wind fields and upward motions from the top of the boundary layer to upper levels.These factors all facilitate the development of deep convection and moisture transport for intense precipitation,and result in its most realistic prediction of the primary rainfall peak.

关键词： PBL parameterization Extreme rainfall high resolution