Characteristics and Preliminary Causes of Tropical Cyclone Extreme Rainfall Events over Hainan Island

The characteristics of tropical cyclone（TC） extreme rainfall events over Hainan Island from 1969 to 2014 are analyzed from the viewpoint of the TC maximum daily rainfall（TMDR） using daily station precipitation data from the Meteorological Information Center of the China Meteorological Administration, TC best-track data from the Shanghai Typhoon Institute,and NCEP/NCAR reanalysis data. The frequencies of the TMDR reaching 50, 100 and 250 mm show a decreasing trend[-0.7（10 yr）^（-1）], a weak decreasing trend [-0.2（10 yr）^（-1）] and a weak increasing trend [0.1（10 yr）^（-1）], respectively. For seasonal variations, the TMDR of all intensity grades mainly occurs from July to October, with the frequencies of TMDR 50 mm and 100 mm peaking in September and the frequency of TMDR 250 mm [TC extreme rainstorm（TCER） events]peaking in August and September. The western region（Changjiang） of the Island is always the rainfall center, independent of the intensity or frequencies of different intensity grades. The causes of TCERs are also explored and the results show that topography plays a key role in the characteristics of the rainfall events. TCERs are easily induced on the windward slopes of Wuzhi Mountain, with the coordination of TC tracks and TC wind structure. A slower speed of movement, a stronger TC intensity and a farther westward track are all conducive to extreme rainfall events. A weaker northwestern Pacific subtropical high is likely to make the 500-h Pa steering flow weaker and results in slower TC movement, whereas a stronger South China Sea summer monsoon can carry a higher moisture flux. These two environmental factors are both favorable for TCERs.

Sideswiping Tropical Cyclones and Their Associated Precipitation over China

Tropical cyclone(TC)precipitation(TCP)has attracted considerable attention in recent decades because of its adverse socioeconomic impacts.In particular,considerable effort has been devoted to quantifying TCP and investigating the precipitation of TCs that make landfall.However,precipitation over land induced by TCs that do not make landfall(i.e.,offshore),the so-called"sideswiping"TCs(STCs),is an important component of TCP but has attracted little attention from the research community to date.Here,best-track and daily precipitation data from the China Meteorological Administration during the 59 years of 1960-2018 are used to study STC precipitation(STP).Results show that:(i)the annual number of STCs fluctuates significantly from 3 to 17,with a mean frequency of 8.8 STCs per year;(ii)there are decreasing trends in STC frequency and STP amount over the past 59 years;(iii)both STC frequency and STP are high from July to October,with maxima in August;(iv)the distribution of STP,covering most of China’s coastal regions,is dominated by intense STCs,and the annual STP decreases from southeast coastal regions to northwest inland areas,with a maximum value over the islands of Taiwan and Hainan;and(v)extreme STP events could appear not only over the island and coastal areas,but also over inland areas such as Zhumadian of Henan Province due to the influences of local orography and favorable largescale forcing.

Establishment of an Objective Standard for the Definition of Binary Tropical Cyclones in the Western North Pacific

To develop an objective standard for defining binary tropical cyclones(BTCs)in the western North Pacific(WNP),two best-track datasets,from the China Meteorological Administration and the Joint Typhoon Warning Center,were adopted for statistical analyses on two important characteristics of BTCs-two TCs approaching each other,and counterclockwise spinning.Based on the high consistency between the two datasets,we established an objective standard,which includes a main standard for defining BTCs and a secondary standard for identifying typical/atypical BTCs.The main standard includes two requirements:two coexisting TCs are a pair of BTCs if(i)the separation distance is≤1800 km,and(ii)this separation maintains for at least 12 h.Meanwhile,the secondary standard defines a typical BTC as one for which there is at least one observation when the two TCs approach each other and spin counterclockwise simultaneously.Under the standard,the ratio of typical BTCs increases as the BTC duration increases or the minimum distance between the two TCs decreases.Then,using the JTWC dataset,it was found that there are 505 pairs of BTCs during the period 1951−2014,including 328 typical BTCs and 177 atypical BTCs,accounting for 65.0%and 35.0%of the total,respectively.In addition,a study of two extreme phenomena-the maximum approaching speed and the maximum counterclockwise angular velocity in typical BTCs-shows that the configuration of the circulation conditions and the distribution of the BTCs favor the formation of these extreme phenomena.

Changes in Typhoon Regional Heavy Precipitation Events over China from 1960 to 2018

In earlier studies,objective techniques have been used to determine the contribution of tropical cyclones to precipitation(TCP)in a region,where the Tropical cyclone Precipitation Event(TPE)and the Regional Heavy Precipitation Events(RHPEs)are defined and investigated.In this study,TPE and RHPEs are combined to determine the Typhoon Regional Heavy Precipitation Events(TRHPEs),which is employed to evaluate the contribution of tropical cyclones to regional extreme precipitation events.Based on the Objective Identification Technique for Regional Extreme Events(OITREE)and the Objective Synoptic Analysis Technique(OSAT)to define TPE,temporal and spatial overlap indices are developed to identify the combined events as TRHPE.With daily precipitation data and TC best-track data over the western North Pacific from 1960 to 2018,86 TRHPEs have been identified.TRHPEs contribute as much as 20%of the RHPEs,but100%of events with extreme individual precipitation intensities.The major TRHPEs continued for approximately a week after tropical cyclone landfall,indicating a role of post landfall precipitation.The frequency and extreme intensity of TRHPEs display increasing trends,consistent with an observed positive trend in the mean intensity of TPEs as measured by the number of daily station precipitation observations exceeding 100 mm and 250 mm.More frequent landfalling Southeast and South China TCs induced more serious impacts in coastal areas in the Southeast and the South during 1990-2018 than1960-89.The roles of cyclone translation speed and"shifts"in cyclone tracks are examined as possible explanations for the temporal trends.

Recent advances in landfalling tropical cyclone asymmetric rainfall mechanism and forecast verification over China

Held every four years,the International Workshop on Tropical Cyclone(IWTC)organized by the World Meteorological Organization has been a global leading conference in thefield of tropical cyclone.In preparation for the 10th IWTC(IWTC-10)in December 2022,a summary of research advances of landfalling tropical cyclone(LTC)rainfall during past four years of 2019–2022 has been prepared.Some of the latest research advances has been summarized in Lamers et al.(2023),which reviewed the latest forecast and disaster prevention methods related to TC precipitation.As a supplement,this article mainly focuses on the recent advances in LTC asymmetric rainfall evolution mechanisms and forecast verification results over China.Some newfindings have been made in the LTC inner-core size relationship with the asymmetric rainfall distri-bution.Some major advances focused on asymmetric microphysical characteristics in the TC rainbands.Current simulation and forecast per-formances of LTC precipitation have been analyzed,and different forecast error sources for rainfall during different landfall stages of TC were compared.To estimate the risk of TC rainfall hazards in China,a parameterized Tropical Cyclone Precipitation Model was reviewed as well in this article.

工程渣土资源化基础问题与低碳技术路径

本文针对国内工程渣土排放量大但高附加值利用率低、资源化过程碳排放高等难题,探究了技术层面的基础问题,并提出了可行的创新技术路径:阐明了工程渣土的定义、成分与危害,并将现有资源化处置技术概括分成4类;梳理了国内近20年工程渣土的4类处置与资源化技术发展脉络与地区差异,分析了技术的主要研发与应用方向,明晰并界定了技术术语;进一步探明了工程渣土的基本性质,厘清了直接再利用、简单处理与改良、固化以及烧制4类技术的科学原理.根据国内工程渣土的处置现状,深入剖析了工程渣土资源化利用率低在技术层面的基础问题,分析了资源化处置的减排潜力.结合我国的碳达峰、碳中和战略,提出了多路径多场景利用、协同处置、数字化技术赋能等创新性解决路径与高附加值策略,并建议了具有潜力的低碳新技术以及工程渣土综合利用的低碳技术路径.

CHANGES IN MONSOON AND TROPICAL CYCLONE EXTREME PRECIPITATION IN SOUTHEAST CHINA FROM 1960 TO 2012

Using daily precipitation data from 110 stations in Southeast China from 1960 to 2012,the extreme precipitation(EP)events associated with monsoon and tropical cyclones were examined using the Objective Synoptic Analysis Technique.In Southeast China,the extreme precipitation associated with tropical cyclones(TEP),which mainly occur in the summer(July–September),accounted for 27.9%of the total extreme precipitation amount,with 40–50%in the coastal regions.While the regional mean TEP amount showed an inconspicuous trend,total EP and monsoon EP(MEP)both showed an increasing trend,with the MEP trend being statistically significant.Although there was little change in the frequency of tropical cyclones affecting Southeast China,the TEP contribution to frequency increased with increasing EP threshold and the frequency of TEP with daily precipitation of more than 300 mm showed an increasing trend in the background of global climate change.The upward trend in the highest-threshold TEP events presents a challenge for mitigation of the damage associated with tropical cyclones.

An application of the LTP＿DSEF model to heavy precipitation forecasts of landfalling tropical cyclones over China in 2018

Recently, a track-similarity-based Dynamical-Statistical Ensemble Forecast(LTP_DSEF) model has been developed in an attempt to predict heavy rainfall from Landfalling Tropical cyclones(LTCs). In this study, the LTP_DSEF model is applied to predicting heavy precipitation associated with 10 LTCs occurring over China in 2018. The best forecast scheme of the model with optimized parameters is obtained after testing 3452 different schemes for the 10 LTCs. Then, its performance is compared to that of three operational dynamical models. Results show that the LTP_DSEF model has advantages over the three dynamical models in predicting heavy precipitation accumulated after landfall, especially for rainfall amounts greater than 250 mm. The model also provides superior or slightly inferior heavy rainfall forecast performance for individual LTCs compared to the three dynamical models. In particular, the LTP_DSEF model can predict heavy rainfall with valuable threat scores associated with certain LTCs, which is not possible with the three dynamical models. Moreover, the model can reasonably capture the distribution of heavier accumulated rainfall, albeit with widespread coverage compared to observations. The preliminary results suggest that the LTP_DSEF model can provide useful forecast guidance for heavy accumulated rainfall of LTCs despite its limited variables included in the model.

Typhoon disaster risk zoning for China’s coastal area

Previous studies on typhoon disaster risk zoning in China have focused on individual provinces or small-scale areas and lack county-level results.In this study,typhoon disaster risk zoning is conducted for China’s coastal area,based on data at the county level.Using precipitation and wind data for China and typhoon disaster and social data at the county level for China’s coastal area from 2004 to 2013,first we analyze the characteristics of typhoon disasters in China’s coastal area and then develop an intensity index of factors causing typhoon disasters and a comprehensive social vulnerability index.Finally,by combining the two indices,we obtain a comprehensive risk index for typhoon disasters and conduct risk zoning.The results show that the maximum intensity areas are mainly the most coastal areas of both Zhejiang and Guangdong,and parts of Hainan Island,which is similar to the distribution of typhoon disasters.The maximum values of vulnerability in the northwest of Guangxi,parts of Fujian coastal areas and parts of the Shandong Peninsula.The comprehensive risk index generally decreases from coastal areas to inland areas.The high-risk areas are mainly distributed over Hainan Island,south-western Guangdong,most coastal Zhejiang,the coastal areas between Zhejiang and Fujian and parts of the Shandong Peninsula.

Comparison of Two Drought Indices in Studying Regional Meteorological Drought Events in China

The composite-drought index （CI）, improved weighted average of precipitation index （IWAP）, and the objective identification technique for regional extreme events （OITREE） were employed to detect China＇s regional meteorolo- gical drought events （CRMDEs） during 1961-2010. Compared with existing references, CI and IWAP both showed strong ability in identifying CRMDEs. Generally, the results of CI and IWAP were consistent, especially for extreme and severe CRMDEs. During 1961-2010, although the frequencies of extreme and severe CRMDEs based on C! and IWAP both showed weak decreasing trends, the two mean-integrated indices both showed increasing but not signifi- cant trends. However, the results of IWAP were more reasonable than CI＇s in two aspects. Firstly, the monthly fre- quency of extreme and severe CRMDEs based on IWAP showed a clear seasonal variation, which coincided with the seasonal variation of the East Asian monsoon over central-eastern China, whereas the frequency based on CI presen- ted a much weaker seasonal variation. Secondly, the two sets of results were sometimes inconsistent with respect to the start and end times of a CRMDE, and CRMDEs based on CI generally showed two unreasonable phenomena： （1） under non-drought conditions, a severe drought stage could suddenly occur in a large area; and （2） during the follow- ing period, drought could alleviate gradually in cases of non-precipitation. Comparative analysis suggested that the IWAP drought index possesses obvious advantages in detecting and monitoring regional drought events.