Temporal Variability of Extreme Precipitation in Jiangxi during 1961-2018

Using 58 years (1961 to 2018) of daily rainfall data, this study focuses on determining trends in the annual and seasonal precipitation extremes of Jiangxi, China, by choosing four extreme precipitation indices, including strong precipitation amount (SPA), mean precipitation intensity (MPI), strong precipitation days (SPD), and strong precipitation frequency (SPF). The monotonic trends are tested by using the Mann-Kendall test for the trends and Sen’s method for the magnitude of the trends. The effective sample size (ESS) method was used to eliminate the influence of serial correlation in the Mann-Kendall test. The results indicated that station Zixi had the strongest extreme precipitation, while Wanzai had the weakest. The trends for each index showed an obvious regional feature over Jiangxi. Increasing trends in annual extreme precipitation indices were found at almost all stations, and the annual variability of the extreme precipitation indices was pronounced, especially for the mean precipitation intensity and the strong precipitation frequency;the majority of these positive trends were shown by the statistical tests. In spring, four indices exhibited significant increasing trends in Northeast and Southwest Jiangxi;however, in summer, only MPI had a remarkable positive trend across almost all of Jiangxi. For the other indices, few stations had remarkable trends. In autumn, MPI and SPF showed remarkable increasing trends in most regions of Jiangxi, while SPA and SPD showed increasing trends at only 6 stations and 3 stations, respectively, which were scattered in the northern and middle parts. In winter, the stations with remarkable upward trends in SPA and SPD were mainly located in the middle of the region, whereas the significant patterns of MPI and SPF were located in the south and middle of the region.

Relationship and Variability of Atmospheric Precipitation Characteristics in the North-West of Ukraine

The paper deals with the issues of differentiation of atmospheric precipitation into gradations according to their characteristics and established meteorological practices.The division of atmospheric precipitation into gradations allows one to have an idea of the possible consequences of their fallout on life in the area.The dependence of the average intensity of precipitation on their duration for the entire series of observations is not described by a power-law dependence with a sufficient degree of reliability,and when differentiating into gradations according to the amount of precipitation(<2.5 mm,2.5-10 mm,≥10 mm),the dependences are obtained with a high degree of correlation.The scatter of points can be explained by the presence of intermediate categories of precipitation,which does not take into account the accepted division of the data.Thus,for large values of the amount of precipitation,the existence of a sepa­rate curve is possible,since the existing classifications of precipitation imply the division of heavy showers into sepa­rate gradations.Differentiation of rains by their duration shows a stronger stratification of the field of points for shorter rains(up to 60 minutes).This stratification of the field of points is successfully differentiated into shorter segments of 20,30 minutes.Associated with the greater heterogeneity of shorter precipitation,it can be both rains of low intensi­ty and heavy downpours of short duration.The probability of the position of the maximum intensity of precipitation during rain has more significant differences for precipitation less than 2.5 mm(the curves are more curved).For rains with a precipitation amount of 2.5 mm or more,the probability curves approach straight lines,which is associated with greater heterogeneity of precipitation less than 2.5 mm.

Distribution of Convective Intensities in West Africa Using Reflectivity and Ice Scattering Characteristics from TRMM Precipitation Features

An evaluation of Radar Precipitation Feature (RPF) characteristics and distribution of convective intensity is performed across 12 regions in West Africa. Results presented in this study have shown that these characteristics over West Africa revealed interesting results which were not observed on a larger spatial scale. The ice scattering characteristics and heights attained by the 15, 20, 30, and 40 dBZ echoes show patterns that agree with the season and movement of the Inter-Tropical Discontinuity (ITD). Some locations in the Western-coast rainforest, Nigeria/Cameroon rainforest and South Sudan savannah had strong potential for convective intensity during MAM, JJA, and SON as shown by their 37-GHz and 85-GHz PCT which fell below 250 K and 225 K respectively while the maximum height attained by their 20 dBZ, 30 dBZ and 40 dBZ are well above the freezing level in those locations. One result revealed a location on the eastern part of south-central Sahel (SC Sahel) where the maximum height attained by the 30 dBZ reflectivity is above 12 km and the maximum height attained by the 40 dBZ reflectivity is above 10 km during SON. The 37-GHz and 85-GHz PCT for this particular location are below 215 K and 150 K respectively indicating a very strong potential for intense convection and hence destructive storms. The distribution of convective intensity, considering only the 85-GHz PCT ice scattering signature, revealed that the percentage of convective intensity increases, especially in the rainforest and savannah, as the ITD shifts northwards during MAM, JJA and during its retreat in SON.

ANALYSIS OF TROPICAL CYCLONE PRECIPITATION FOR DIFFERENT INTENSITY CLASS IN NORTHWEST PACIFIC WITH TRMM DATA

Combined with TRMM products and Tropical Cyclone(TC) best track data in Northwest Pacific from 1 January 2003 to 31 December 2009,a total of 118 TCs,including 336 instantaneous TC precipitation observations are established as the TRMM TC database,and the database is stratified into four intensity classes according to the standard of TC intensity adopted by China Meteorological Administration(CMA):Severe Tropical Storm(STS),Typhoon(TY),Severe Typhoon(STY) and Super Typhoon(SuperT Y).For each TC snapshot,the mean rainfall distribution is computed using 10-km annuli from the TC center to a 300-km radius,then the axisymmetric component of TC rainfall is represented by the radial distribution of the azimuthal mean rain rate;the mean rain rates,rain types occurrence and contribution proportion are computed for each TC intensity class;and the mean quadrantal distribution of rain rates along TCs motion is analyzed.The result shows that:(1) TCs mean rain rates increase with their intensity classes,and their radial distributions show single-peak characteristic gradually,and furthermore,the characteristics of rain rates occurrence and contribution proportion change from dual-peak to single-peak distribution,with the peak rain rate at about 5.0mm/h;(2) Stratiform rain dominate the rain type in the analysis zone,while convective rain mainly occurred in the eye-wall region;(3) The values of mean rain rate in each quadrant along TCs motion are close to each other,relatively,the value in the right-rear quadrant is the smallest one.

Trends in Graded Precipitation in China from 1961 to 2000

Daily precipitation rates observed at 576 stations in China from 1961 to 2000 were classified into six grades of intensity, including trace （no amount）, slight （≤ 1 mm d^-1）, small, large, heavy, and very heavy. The last four grades together constitute the so called effective precipitation （〉 1 mm d^-1）. The spatial distribution and temporal trend of the graded precipitation days are examined. A decreasing trend in trace precipitation days is observed for the whole of China, except at several sites in the south of the middle section of the Yangtze River, while a decreasing trend in slight precipitation days only appears in eastern China. The decreasing trend and interannual variability of trace precipitation days is consistent with the warming trend and corresponding temperature variability in China for the same period, indicating a possible role played by increased surface air temperature in cloud formation processes. For the effective precipitation days, a decreasing trend is observed along the Yellow River valley and for the middle reaches of the Yangtze River and Southwest China, while an increasing trend is found for Xinjiang, the eastern Tibetan Plateau, Northeast China and Southeast China. The decreasing trend of effective precipitation days for the middle- lower Yellow River valley and the increasing trend for the lower Yangtze River valley are most likely linked to anomalous monsoon circulation in East China. The most important contributor to the trend in effective precipitation depends upon the region concerned.

Precipitation changes in the mid-latitudes of the Chinese mainland during 1960–2014

Based on daily precipitation data from 163 meteorological stations, this study investigated precipitation changes in the mid-latitudes of the Chinese mainland（MCM） during 1960–2014 using the climatic trend coefficient, least-squared regression analysis, and a non-parametric Mann-Kendall test.According to the effects of the East Asian summer monsoon on the MCM and the climatic trend coefficient of annual precipitation during 1960–2014, we divided the MCM into the western MCM and eastern MCM. The western MCM was further divided into the western MCM1 and western MCM2 in terms of the effects of the East Asian summer monsoon. The main results were as follows：（1） During the last four decades of the 20^（th） century, the area-averaged annual precipitation presented a significant increasing trend in the western MCM, but there was a slight decreasing trend in the eastern MCM, where a seesaw pattern was apparent. However, in the 21^（st） century, the area-averaged annual precipitation displayed a significant increasing trend in both the western and eastern MCM.（2） The trend in area-averaged seasonal precipitation during 1960–2014 in the western MCM was consistent with that in the eastern MCM in winter and spring. However, the trend in area-averaged summer precipitation during1960–2014 displayed a seesaw pattern between the western and eastern MCM.（3） On an annual basis,both the trend in rainstorms and heavy rain displayed a seesaw pattern between the western and eastern MCM.（4） The precipitation intensity in rainstorms, heavy rain, and moderate rain made a greater contribution to changes in the total precipitation than precipitation frequency. The results of this study will improve our understanding of the trends and differences in precipitation changes in different areas of the MCM. This is not only useful for the management and mitigation of flood disasters, but is also beneficial to the protection of water resources across the MCM.

Estimation of meteorological drought indices based on AgMERRA precipitation data and station-observed precipitation data

Meteorological drought is a natural hazard that can occur under all climatic regimes. Monitoring the drought is a vital and important part of predicting and analyzing drought impacts. Because no single index can represent all facets of meteorological drought, we took a multi-index approach for drought monitoring in this study. We assessed the ability of eight precipitation-based drought indices（SPI（Standardized Precipitation Index）, PNI（Percent of Normal Index）, DI（Deciles index）, EDI（Effective drought index）, CZI（China-Z index）, MCZI（Modified CZI）, RAI（Rainfall Anomaly Index）, and ZSI（Z-score Index）） calculated from the station-observed precipitation data and the Ag MERRA gridded precipitation data to assess historical drought events during the period 1987–2010 for the Kashafrood Basin of Iran. We also presented the Degree of Dryness Index（DDI） for comparing the intensities of different drought categories in each year of the study period（1987–2010）. In general, the correlations among drought indices calculated from the Ag MERRA precipitation data were higher than those derived from the station-observed precipitation data. All indices indicated the most severe droughts for the study period occurred in 2001 and 2008. Regardless of data input source, SPI, PNI, and DI were highly inter-correlated（R^2=0.99）. Furthermore, the higher correlations（R^2=0.99） were also found between CZI and MCZI, and between ZSI and RAI. All indices were able to track drought intensity, but EDI and RAI showed higher DDI values compared with the other indices. Based on the strong correlation among drought indices derived from the Ag MERRA precipitation data and from the station-observed precipitation data, we suggest that the Ag MERRA precipitation data can be accepted to fill the gaps existed in the station-observed precipitation data in future studies in Iran. In addition, if tested by station-observed precipitation data, the Ag MERRA precipitation data may be used for the data-lacking areas.

Spatiotemporal analysis of drought variability based on the standardized precipitation evapotranspiration index in the Koshi River Basin, Nepal

Drought is an inevitable condition with negative impacts in the agricultural and climatic sectors,especially in developing countries.This study attempts to examine the spatial and temporal characteristics of drought and its trends in the Koshi River Basin(KRB)in Nepal,using the standardized precipitation evapotranspiration index(SPEI)over the period from 1987 to 2017.The Mann-Kendall test was used to explore the trends of the SPEI values.The study illustrated the increasing annual and seasonal drought trends in the KRB over the study period.Spatially,the hill region of the KRB showed substantial increasing drought trends at the annual and seasonal scales,especially in summer and winter.The mountain region also showed a significant increasing drought trend in winter.The drought characteristic analysis indicated that the maximum duration,intensity,and severity of drought events were observed in the KRB after 2000.The Terai region presented the highest drought frequency and intensity,while the hill region presented the longest maximum drought duration.Moreover,the spatial extent of drought showed a significant increasing trend in the hill region at the monthly(drought station proportion of 7.6%/10 a in August),seasonal(drought station proportion of 7.2%/10 a in summer),and annual(drought station proportion of 6.7%/10 a)scales.The findings of this study can assist local governments,planners,and project implementers in understanding drought and developing appropriate mitigation strategies to cope with its impacts.

Precipitation under Subtropical High Conditions:Evidence and Implications

The impact of the subtropical high (STH) on precipitation was investigated on a daily timescale using matched NCEP and the Global Precipitation Climatology Project (GPCP) datasets.Comparison of the conditional probability (intensity) of precipitation under STH condi-tions with that under non-STH conditions suggests that the presence of the STH conditions has a limited impact on local precipitation.In the West Pacific Subtropical High (WPSH) and the North Atlantic Subtropical High (NASH),precipitation was only 30% lower under STH conditions than under non-STH conditions.The STH conditions had somewhat more impact on precipitation intensity,but it was still 50% less than the intensity under non-STH conditions (mean of roughly 5 mm d 1).Pre-cipitation under STH conditions was found to be highly correlated with vertical motion.Active updrafts occurring even under STH conditions are essential for frequent oc-currences and moderate intensities of precipitation.

The increasing predominance of extreme precipitation in Southwest China since the late 1970s

本文分析了中国西南20世纪70年代末以来极端降水事件的频率,强度及其对总降水的贡献.结果表明,该地区约60%的降水站点极端降水的频率和强度正在增加,而大多数站点总降水频率明显减少.同时极端降水总量对总降水量的贡献有显著增加的趋势,极端降水在日益干旱的中国西南地区变得更具主导性.研究结果提醒应更加重视极端降水及其可能引发的次生灾害,如洪水,山体滑坡等.

Century-long variability and trends in daily precipitation characteristics at three Finnish stations

Long-term variations and trends in a wide range of statistics for daily precipitation characteristics in terms of intensity, frequency and duration in Finland were analysed using precipitation records during 1908e2008 from 3 meteorological stations in the south(Kaisaniemi),centre(Kajaani) and north(Sodankyl€a). Although precipitation days in northern part were more frequent than in central and southern parts, daily precipitation intensity in the south was generally higher than those in the centre and north of the country. Annual sum of very light precipitation(0 mm < daily precipitation long-term 50 th percentile of daily precipitation more than 0 mm) significantly( p < 0.05) decreased over time,with the highest rate in northern Finland. These decreasing trends might be the result of significant increases in frequency of days with very light precipitation at all the stations, with the highest and lowest rates in northern and southern Finland, respectively. Ratio of annual total precipitation to number of precipitation days also declined in Finland over 1908e2008, with a decreasing north to south gradient. However, annual duration indices of daily precipitation revealed no statistically significant trends at any station. Daily precipitation characteristics showed significant relationships with various well-known atmospheric circulation patterns(ACPs). In particular, the East Atlantic/West Russia(EA/WR)pattern in summer was the most influential ACP negatively associated with different daily precipitation intensity, frequency and duration indices at all three stations studied.

Analysis on Summer Precipitation Efficiency in Shenyang

[Objective] The research aimed to analyze summer precipitation efficiency in Shenyang.[Method] By using the method which estimated the cloud water resource,based on the vertical accumulated liquid water content which was observed by 'QFW-1 dual-channel microwave radiometer' and the rain intensity data which had 1min interval and were inverted by 'particle laser-based optical measurement' (Parsivel),the precipitation efficiency in Shenyang area during July-August,2007 was analyzed.[Result] When the rain intensity I<7.5 mm/h,the precipitation efficiency E was stable and was during 3.2%-2.7%.The average value was 3.0%.When the rain intensity I ≥7.5 mm/h,the precipitation efficiency E presented the linear increasing as the rain intensity I increased.The bigger the rain intensity was,the more the remaining liquid water content in the air was,and the bigger the artificial precipitation potential was.[Conclusion] The research provided the guidance role for analyzing the cloud water resource in the air and the artificial precipitation potential.

Intra-Annual Variability of Diurnal Cycle Precipitation over China from 1960–2000

Characteristics of diurnal cycle precipitation over China are investigated using twice-daily observations by the China Meteorological Administration during 1960–2000. Characteristics investigated include nighttime/daytime precipitation amount(PA), intensity, and frequency. Geographically, the region is separated into western and eastern China by the 110°E longitude. Our analysis shows that there generally is more night-time than daytime precipitation in western China, particularly in the Sichuan Basin. Over eastern China, the opposite holds true, particularly along the southeast coast. Regional average monthly daytime and night-time precipitation peaks in the same month for both western and eastern China. Over western China, monthly night-time precipitation is always greater than that during daytime, but the night-time precipitation frequency(PF) is only greater in non-summer(June–August) months. Over eastern China, daytime precipitation is greater than that in the night-time during the warm season(May–August) in both amount and frequency. The night-day difference(night-time minus daytime) in PA over western China is mainly influenced by precipitation intensity, while over eastern China the night-day difference in rainfall amount is mostly driven by PF.

MULTI-TIMESCALE VARIATIONS OF SOMALI JET AND ITS RELATION WITH PRECIPITATION IN CHINA

Based on the ERA reanalysis winds data, the multi-time scale variations of Somali jet are analyzed synthetically. The jet's influences on rainfall in China on interannual, interdecadal and sub-monthly scales are also studied using correlation and composite analyses. The results demonstrate that the interdecadal variations of the jet are significant.The Somali jet became weaker in the 1960 s and became the weakest in the early 1970 s before enhancing slowly in the late 1970 s. Moreover, the relation between the Somali jet and summer precipitation in China is close, but varies on different timescales. Preliminary analysis shows that the intensity variations in May and June during the early days of establishment are well correlated with summer precipitation in China. The Somali jet intensity on the interdecadal scale is closely related with interdecadal variations of the precipitation in China. Regardless of leading or contemporaneous correlation, the correlations between the Somali jet intensity and the rainfall in northern and southern China show obvious interdecadal variations. Moreover, the link between the anomalies of the jet intensity in May-August and precipitation evolution on synoptic scale in China is further studied. China has more rainfall with positive anomalies of the Somali jet but less rainfall with negative anomalies during the active period of the jet. The influence of positive Somali jet anomalies on China precipitation is more evident.

Modeling Rainfall Intensity-Duration-Frequency (IDF) and Establishing Climate Change Existence in Uyo-Nigeria Using Non-Stationary Approach

This study aims at establishing if climate change exists in the Niger Delta environment using non-stationary rainfall Intensity-Duration-Frequency (IDF) modelling incorporating time-variant parameters. To compute the intensity levels, the open-access R-studio software was used based on the General Extreme Value (GEV) distribution function. Among the four linear parameter models adopted for integrating time as a covariate, the fourth linear model incorporating scale and location with the shape function constant produced the least corrected Akaike Information Criteria (AICc), varying between 306.191 to 101.497 for 15 and 1440 minutes, respectively, selected for calibration of the GEV distribution equation. The non-stationary intensities yielded higher values above those of stationary models, proving that the assumption of stationary IDF models underestimated extreme events. The difference of 13.71 mm/hr (22.71%) to 14.26 mm/hr (17.0%) intensities implies an underestimation of the peak flood from a stationary IDF curve. The statistical difference at a 95% confidence level between stationary and non-stationary models was significant, confirming evidence of climatic change influenced by time-variant parameters. Consequently, emphasis should be on applying shorter-duration storms for design purposes occurring with higher intensities to help reduce the flood risk and resultant infrastructural failures.

广东省2024年4月气候概况及极端性分析

2024年4月,广东省平均气温创历史4月新高,4月降水为有气象记录以来最多,但空间分布不均,呈北多南少。月内出现2次冷空气过程,同时先后出现了1981年以来最强的3轮4月份强降水过程,具有强对流明显、暴雨区重叠、累积雨量大、极端性显著的特点。

近62 a华南“龙舟水”气候特征及变化

每年端午节前后龙舟竞渡之时,是华南前汛期降水最多、最为集中的时段,容易引发严重洪涝灾害,并对早稻生产造成严重影响,称之为“龙舟水”。对华南“龙舟水”期间暴雨过程的频次和强度进行研究是当前防灾减灾的迫切需求。利用1961—2022年华南192个国家气象观测站逐日降水资料,采用EOF、线性趋势、M-K突变等方法,分析了华南“龙舟水”期间降水量的时空特征及变化;构建了一个表征华南“龙舟水”暴雨过程的综合强度指数,由此分析华南近62 a“龙舟水”期间暴雨过程频次、强度以及“龙舟水”强度年景指数的特征和变化。结果表明,华南“龙舟水”一致性变化是其最主要的特点。1961—2022年“龙舟水”期间,华南共出现229次暴雨过程,平均每年3.7次。近62 a来华南区域平均“龙舟水”降水量和暴雨过程频次变化趋势不显著,但“龙舟水”强度年景指数以1.2·(10 a)^(-1)的速率显著上升。评估得到近62 a华南“龙舟水”最强暴雨过程出现在2022年6月4—21日,华南“龙舟水”强年有4 a,分别出现在2022年、2020年、2008年和2006年。

常州市主城区高强度降水变化特征及其影响分析

以常州市主城区为研究区域,基于高强度降水指数等指标,分析常州市主城区高强度降水特性及其对城市防汛的影响。研究结果表明,受气候变化和城镇化等影响,常州市主城区在1953—2022年期间有雨日数等3个极端降水日数指标、强降水量等6个高强度降水量级指标均呈递增趋势。

1961-2020年中国降水等级的变化特征

[目的]探究全国各等级降水的时空分布特征及季节变化规律,增强对我国不同等级降水发生规律的认知,进而为提升全国防灾减灾能力提供科技支撑。[方法]基于1961—2020年全国681个气象站点的逐日地面降水资料,分析了全国不同等级降水(小雨、中雨、大雨和暴雨)日数、强度的时空分布特征和季节变化规律。[结果](1)1961—2020年全国小雨日数呈减少趋势,中雨以上等级日数呈增长趋势,除暴雨强度变化幅度较大外,小雨、中雨和大雨强度均无明显变化。秋季小雨日数减幅最大,大雨、暴雨日数在夏季增加最快、秋季最缓,暴雨强度在各季节波动幅度均较大。(2)不同等级降水空间分布有一定差异性,小雨日数高值区主要分布在西南诸河流域,中雨以上等级降水日数以及各等级降水强度均从东南向西北逐渐减小,内陆河流域降水日数、强度均为最小。(3)春、秋、冬三季降水主要集中在东南诸河流域和珠江流域,小雨占主导地位,夏季降水主要集中在西南诸河流域、东南诸河流域和珠江流域。(4)小雨日数的减少在春季和冬季较为明显,东南诸河流域和珠江流域对小雨日数减少起到了很大贡献,中雨以上等级降水日数在各季节大致以上升趋势为主,大雨强度在春季增强、秋季减弱,各流域暴雨强度在春季呈增强趋势。[结论]全国各等级降水在时空分布以及季节尺度上有明显差异,九大流域对全国不同等级降水的贡献作用不尽相同,未来应加强各流域主要环流系统及水循环等对不同等级降水影响的研究。

中国昼夜降水特征的空间分异规律

降水昼夜分配的时空特征,是干旱半干旱地区降水资源有效性的重要影响因素。我国昼夜降水空间分异复杂,在雨强、高程、季相等方面的规律还有待进一步研究。为此,采用空间分区、高程分带、雨强分级、季相对比等方法,基于全国839个气象站点1951~2019年的降水资料,研究了我国昼夜降水特征的空间分异规律。结果表明,在空间分区上,我国可划分为受夜间冷却和山谷风效应的青藏及周边夜雨典型区、受辐射对流效应的秦-淮以南昼雨典型区、秦-淮以北降水昼夜相对均衡区;在垂直分异方面,青藏高原及周边山地最为明显,年夜间降水量的高程递减率大于昼间,昼夜差异随海拔升高而减弱;降水的雨强特征为中高雨强降水比重大,尤其是青藏东缘中高强度夜雨显著;季相规律为青藏及西南地区月降水均为夜雨大于昼雨,而南方4~10月昼雨典型。我国昼夜降水特征的空间分异规律,可作为农业与生态水资源气候评估的参考,对山洪预警也有重要意义。