TEMPERATURE,RAINFALL VARIATIONS AND THEIR ANOMALIES OVER CHINA UNDER THE COLD-WARM BACKGROUND IN THE 20TH CENTURY

In this study,the climate trend of the annual average air temperature and total annual rainfall inChina in the present century has been examined.It is noted that in the Northwest,the Northeast andNorth China the climate has become notably warmer this century but the rainfall trend has not beenevident,mainly negative.In the 1980s China's rainfall and temperature showed noticeable regionalfeatures: warm and dry in North China,cold and dry in the Southwest,warm and wet in theNortheast,cold and wet in the middle-lower reaches of the Changjiang River.Besides,the fourinterdecadal climate change features and ranges of this century have been studied.It is found that onthe scale of several decades there was considerably less rainfall in the most part of China in the warmbackground than in the cold background.The increase of temperature which started from the 1970smainly happened in the Northwest and Northeast,while to the south of the Huanghe River thetemperature increase did not even as great as in 1940s.The corresponding rainfall feature is that mostareas experienced much less rainfall except the area to the south of the Huanghe River and over theChangjiang and Huaihe River basin.     

TEMPERATURE, RAINFALL VARIATIONS AND THEIR ANOMALIES OVER CHINA UNDER THE COLD-WARM BACKGROUND IN THE 20TH CENTURY*

In this study,the climate trend of the annual average air temperature and total annual rainfall in China in the present century has been examined.It is noted that in the Northwest,the Northeast and North China the climate has become notably warmer this century but the rainfall trend has not been evident,mainly negative.In the 1980s China's rainfall and temperature showed noticeable regional features:warm and dry in North China,cold and dry in the Southwest,warm and wet in the Northeast,cold and wet in the middle-lower reaches of the Changjiang River.Besides,the four interdecadal climate change features and ranges of this century have been studied.It is found that on the scale of several decades there was considerably less rainfall in the most part of China in the warm background than in the cold background.The increase of temperature which started from the 1970s mainly happened in the Northwest and Northeast,while to the south of the Huanghe River the temperature increase did not even as great as in 1940s.The corresponding rainfall feature is that most areas experienced much less rainfall except the area to the south of the Huanghe River and over the Changjiang and Huaihe River basin.     

东亚夏季风的变化及对松嫩流域旱涝影响

根据近50年来美国NCEP/NCAR再分析资料及松嫩流域39个站1951~2000年的逐日降水资料,用相关分析、合成、对比分析及小波分析等方法分析了东亚夏季风的年际、年代际变化及对松嫩流域旱涝的影响。结果表明,东亚夏季风对位于中高纬度的松嫩流域的旱涝趋势确有影响,但东亚夏季风的年际、年代际变化很大。东亚夏季风与松嫩流域盛夏降水特点相似:都具有3~5年、10~12年的变化周期,在20世纪60年代末、80年代初都有气候突变。松嫩流域的旱涝趋势除与东亚夏季风有关外,还与中高纬度的西风带天气系统及西太平洋副热带高压密切相关。     

长江流域1960-2004年极端强降水时空变化趋势

Recent trends of the rainfall, intensity and frequency of extreme precipitation (EP) over the Yangtze River Basin are analyzed in this paper. Since the mid-1980s the rainfall of EP in the basin has significantly increased, and the most significant increment occurred in the southeast mid-lower reaches, and southwest parts of the basin. Summer witnessed the most remarkable increase in EP amount. Both the intensity and frequency of EP events have contributed to the rising of EP amount, but increase in frequency contributed more to the increasing trend of EP than that in intensity. The average intervals between adjacent two EP events have been shortened. It is also interesting to note that the monthly distribution of EP events in the upper basin has changed, and the maximum frequency is more likely to occur in June rather than in July. The synchronization of the maximum frequency month between the upper and mid-lower reaches might have also increased the risk of heavy floods in the mid-lower reaches of the Yangtze River.     

1951-2006年黄河和长江流域雨涝变化分析

 根据1951-2006年黄河和长江流域雨涝灾害灾情统计资料,分析了两个流域雨涝灾害发生频率的时空分布特征,结果表明：近50 a以来,特别是20世纪80年代以来,受气候变化影响,黄河和长江流域雨涝灾害不断增加,农作物受灾、成灾面积呈增加趋势,损失日趋严重,且长江流域受雨涝灾害影响范围较大,灾害发生频率大于黄河流域。受暴雨影响,夏季两个流域雨涝发生频率最高、范围最广。20世纪80年代末以来,黄河流域雨涝灾害增加趋势较为明显,而长江流域80年代初雨涝受灾面积和成灾面积显著增加。两个流域雨涝灾害的受灾率均自上游至下游逐渐增加,其中长江流域中下游地区受雨涝灾害影响较大。     

CWRF模式对长江流域极端降水气候事件的模拟能力评估

基于1980—2016年长江流域站点观测降水,评估了CWRF区域气候模式对长江流域面雨量和极端降水气候事件的模拟能力.结果表明:CWRF模式能较好地再现1980—2016年长江流域及不同分区降水空间分布及月/季面雨量年际变率,且在冬、春季表现较好,夏、秋季次之.CWRF模式对长江流域面雨量存在系统性高估,对面雨量的模拟...     

2050年前长江流域极端降水预估

20世纪90年代长江流域日最大降水增加主要出现在长江以南地区和金沙江流域,ECHAM5/MPI-OM模型也大致模拟出了这种趋势。在IPCC给出的3种不同的排放情景下,2000-2050年长江上游日最大降水均有上升趋势,2020年前A2情景下日最大降水最大,A1B最小;长江中下游日最大降水在2025年之前均有明显上升趋势,之后略有下降,波动较大。长江流域未来日最大降水增多的区域可能主要出现在长江以南地区,而极端降水减少的区域可能出现在长江以北地区。     

近50a江淮地区梅雨期水汽输送特征研究

利用1958—2007年ERA再分析风场及气压场资料和APHRO高分辨率逐日降水资料,对近50 a来梅雨期水汽输送的时空特征及其与江淮地区降水的关系进行了研究,发现各条水汽通道对江淮地区梅雨期降水强度及范围的影响程度均不同。梅雨期影响我国降水的水汽输送有显著的年际变化,并且水汽输送强弱年对应江淮地区降水强度也有明显差异。相关分析及合成差值的结果显示,西太平洋水汽输送贡献更大,且西太平洋水汽输送(东南通道)增强时,江淮地区降水增多。印度洋水汽输送的加强会减弱太平洋的水汽输送从而使得江淮少雨。在全球变暖的背景下,西太平洋的水汽输送对降水的增强作用有所减弱而印度洋输送所导致降水强度减弱的范围则明显扩大。自1980年起,江淮降水出现缓慢增多的趋势与全球变暖所导致的东亚环流异常进而影响水汽输送异常相关。     

Assessing the Seasonal Predictability of Summer Precipitation over the Huaihe River Basin with Multiple APCC Models

Seasonal rainfall predictability over the Huaihe River basin is evaluated in this paper on the basis of 23-year(1981-2003) retrospective forecasts by 10 climate models from the Asia-Pacific Economic Cooperation(APEC) Climate Center(APCC) multi-model ensemble(MME) prediction system.It is found that the summer rainfall variance in this basin is largely internal,which leads to lower rainfall predictability for most individual climate models.By dividing the 10 models into three categories according to their sea surface temperature(SST) boundary conditions including observed,predicted,and persistent SSTs,the MME deterministic predictive skill of summer rainfall over Huaihe River basin is investigated.It is shown that the MME is effective for increasing the current seasonal forecast skill.Further analysis shows that the MME averaged over predicted SST models has the highest rainfall prediction skill,which is closely related to model’s capability in reproducing the observed dominant modes of the summer rainfall anomalies in Huaihe River basin.This result can be further ascribed to the fact that the predicted SST MME is the most effective model ensemble for capturing the relationship between the summer rainfall anomalies over Huaihe River basin and the SST anomalies(SSTAs) in equatorial oceans.     

The Seasonal Prediction of the Exceptional Yangtze River Rainfall in Summer 2020

During June and July of 2020, the Yangtze River basin suffered from extreme mei-yu rainfall and catastrophic flooding. This study explores the seasonal predictability and associated dynamical causes for this extreme Yangtze River rainfall event, based on forecasts from the Met Office GloSea5 operational forecast system. The forecasts successfully predicted above-average rainfall over the Yangtze River basin, which arose from the successful reproduction of the anomalous western North Pacific subtropical high (WNPSH). Our results indicate that both the Indian Ocean warm sea surface temperature (SST) and local WNP SST gradient were responsible for the westward extension of the WNPSH, and the forecasts captured these tropical signals well. We explore extratropical drivers but find a large model spread among the forecast members regarding the meridional displacements of the East Asian mid-latitude westerly jet (EAJ). The forecast members with an evident southward displacement of the EAJ favored more extreme Yangtze River rainfall. However, the forecast Yangtze River rainfall anomaly was weaker compared to that was observed and no member showed such strong rainfall. In observations, the EAJ displayed an evident acceleration in summer 2020, which could lead to a significant wind convergence in the lower troposphere around the Yangtze River basin, and favor more mei-yu rainfall. The model forecast failed to satisfactorily reproduce these processes. This difference implies that the observed enhancement of the EAJ intensity gave a large boost to the Yangtze River rainfall, hindering a better forecast of the intensity of the event and disaster mitigation.     

2007年夏季淮河流域洪涝与亚洲地区大气低频振荡的关系

利用NCEP/NCAR再分析资料和我国地面观测站的逐日降水资料, 研究了2007年夏季淮河流域洪涝与亚洲地区大气低频振荡的联系, 通过分析研究表明: 2007年夏季淮河流域降水低频振荡的主要周期是30～70天, 该低频序列的方差大约占了总方差的47%; 在降水低频振荡的位相5～8 (1～4), 亚洲季风区从阿拉伯海北部经孟加拉湾到我国南海地区, 以及我国淮河流域经渤海到日本地区主要受低频热源 (热汇) 的控制; 并且在极大降水位相7, 我国东部地区 (10°N～45°N, 110°E～120°E), 从北到南, 〈Q1〉低频分量的分布呈负正相间的低频热汇、 热源、 热汇、 热源形式(位相3则呈相反的分布形式); 在位相5～8 (1～4), 亚洲季风区〈Q1〉低频分量的分布有利于 (不利于) 气流向淮河流域汇合并形成辐合上升; 受低频环流变化的影响, 在位相5～8, 大量的水汽被输送到淮河流域, 辐合上升形成降水; 相反, 在位相1～4, 来自西太平洋上的水汽在该地区辐散, 不利于降水的发生。     

海河流域不同地形站网密度对面雨量分析精度的影响

利用2011-2013年汛期逐时降水量资料,将国家常规站与区域加密站进行分拣合成,通过面雨量离差系数、面雨量比值系数、点面关系综合分析不同地形条件下站网密度对海河流域各水系面雨量计算精度的影响。结果表明：站网密度是影响面雨量计算精度的重要因素,对不同地形面雨量分析存在不同程度的影响。其中,混合地貌水系中地形分布、降水分布差异尤为明显的滦河水系影响最大,站网密度较低的常规站对面雨量估计比高站网密度的合成站平均偏高2.5 mm,12%误差超过5 mm;其次山区永定河水系低站网密度常规站对面雨量估计平均偏高1.5 mm,相对误差达80.3%,尤其局地性短时强降水时,面雨量分析误差高达10倍以上;此外,混合地貌水系北三河、南运河站网密度对面雨量影响程度略低于滦河水系,平原区徒骇马颊河以及混合地貌中地形差异较小的大清河、子牙河影响较低。     

西北太平洋夏季风对中国长江流域夏季降水的影响

利用1979～2005年NCEP/NCAR的环流场再分析资料和降水资料, 通过对季风期降水、 大气环流、 水汽输送及低频振荡等方面的分析, 分别从时间和空间上分析了西北太平洋夏季风与中国长江流域夏季降水的联系。结果表明:(1) 西北太平洋夏季风与中国长江流域夏季降水存在显著的负相关关系, 在西北太平洋夏季风强盛时, 副热带高压异常偏北, 其西侧的偏南气流异常偏弱, 使得我国长江流域形成低层异常环流及水汽输送的辐散区, 从而造成长江流域夏季降水偏少; 而在西北太平洋夏季风减弱的年份, 西太平洋副高异常偏南偏西, 在长江流域以南地区形成异常偏强的偏南风水汽输送, 使得长江流域成为南、 北距平风的汇合区, 其上空对流活动异常活跃, 非常有利于长江流域的降水。 (2) 东亚局地Hadley垂直环流在强、 弱季风年也显著不同, 在强季风年里, Hadley局地环流异常偏弱, 长江流域上空出现的下沉运动距平, 使得该地区降水减弱, 而弱季风年则正好相反。 (3) 西北太平洋夏季风存在显著的气候平均的大气季节内振荡 (CISO), 在西北太平洋夏季风减弱时期, 长江流域降水同时受到源自热带西北太平洋西传CISO和源自热带印度洋东传CISO的共同影响, 可能造成了某种锁相关系, 从而造成降水偏多; 而在强季风年里长江流域只受由西太平洋西传的CISO的影响, 不容易激发降水。     

A STUDY ON RESPONSE OF PRECIPITATION IN CHINA TO MONSOON INTRASEASONAL OSCILLATION

Temporal and spatial evolution characteristics of the 30-60 day oscillation (intraseasonal oscillation, ISO) of summer rainfall in China and the effects of East Asian monsoon on the rainfall ISO are analyzed in this paper. Results show that the annual and decadal variations of the oscillation exist between 1960 and 2008, and the intensity is weakest in the late 1970s and early 1980s. In the typical strong years of the rainfall ISO obtained from empirical orthogonal functions (EOF mode 1), an anticyclone is in northwestern Pacific and a cyclone is in the east of China. In the typical weak years, the wind ISO is much weaker. The low-frequency zonal wind and water vapor transport from the low latitudes to mid-latitudes in the typical strong years, and the oscillation strength of diabatic heating is much stronger than that in the weak years of the rainfall ISO. The anomaly characteristics of the rainfall ISO show anti-phases between the Yangtze River basin and south of China. As for the typical strong years of the rainfall ISO in the Yangtze River basin (EOF mode 2), the main oscillation center of water vapor is in the east of China (20-30°N, 110-130°E). In the peak (break) phase of the rainfall oscillation, a low-frequency cyclone (anticyclone) is in the Yangtze River basin and an anticyclone (cyclone) is near Taiwan Island. In addition, the peak rainfall corresponds to the heat source in the Yangtze River basin and the heat sink in the Qinghai-Tibet Plateau. As for the typical strong years of the rainfall ISO in the south of China, the main oscillation center of water vapor is south of 20°N. In the peak (break) phase of the rainfall ISO, a low-frequency cyclone (anticyclone) is in the south of China and an anticyclone (cyclone) is in the Philippines. The peak rainfall corresponds to the heat source in the south of China and the South China Sea, and the heat sink in the west of Indochina.     

RegCM3对全球变暖背景下中国东部季风降水和雨型变化的模拟

The authors investigate possible changes of monsoon rainfall and associated seasonal (June-JulyAugust) anomaly patterns over eastern China in the late 21st century under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios (SRES) A2 emission scenario as simulated by a high-resolution regional climate model (RegCM3) nested in a general circulation model (FvGCM/CCM3).Two sets of multi-decadal simulations are performed at 20-km grid spacing for present day and future climate conditions.Results show that the RegCM3 reproduces the mean rainfall distribution;however the evolution of the monsoon rain belt from South China to North China is not well simulated.Concerning the rain pattern classifications,RegCM3 overestimates the occurrence of Pattern 1 (excessive rainfall in northern China) and underestimates that of Pattern 2 (increased rainfall over the Huai River basin).Under future climate conditions,RegCM3 projects less occurrence of Pattern 1,more of Pattern 2,and little change of Pattern 3 (rainfall increase along the Yangtze River).These results indicate that there might be increased rainfall over the Huai-Yellow River area and reduced rainfall over North China in the future,while rainfall over the lower reaches of the Yangtze River basin is not modified significantly.Uncertainties exist in the present study are also discussed.     

Projection of Future Precipitation Extremes Change (2001-2050) in the Yangtze River Basin

 Daily maximum rainfall (R1D) was higher in the Jialing River basin, the Taihu Lake area and the mid-lower main stream section of the Yangtze River basin in the 1990s, and there was a good relationship between ECHAM5/MPI-OM model simulation and the observed data about extreme precipitation (R1D). Under the IPCC SRES A2, A1B, and B1 scenarios, R1Ds are all projected to be in increasing trends in the upper Yangtze River basin during 2001-2050, and R1D shows a more significant increasing tendency under the A2 scenario when compared with the A1B scenario before 2020. With respect to the middle and lower Yangtze River basin, an increasing tendency is projected before 2025, and since then the increasing tendency will become insignificant. There might be more floods to the south of the Yangtze River and more droughts to the north in the next decades.     

A STUDY ON RELATION BETWEEN EAST ASIAN WINTER MONSOON AND CLIMATE CHANGE DURING RAINING SEASON IN CHINA

1 INTRODUCTION The Asian monsoon and its anomalies play an important role in the global general circulation and climatic change. As an essential component of the monsoon system, the East Asian winter monsoon is not only the most vigorous across the globe …     

祖厉河流域近50a降水变化及典型人类活动对降水的影响

对祖厉河流域近50 a 降水资料的分析结果表明:祖厉河主流域区等降水量线纬向分布特征明显,降水量随纬度增高而减少;在流域南部和东北部高度差大的地方,降水量随高度增高而增加;受地形影响,祖厉河中下游有一条干舌自西北向东南伸到流域东部边缘,与周边区域相比,干舌区降水偏少90～140 mm.近50 a祖厉河流域降水显著减少,区域平均减少106.4 mm.小波分析表明,25 a以上和10 a左右的降水变化周期很明显,目前处于偏少期;区域平均降水量从20世纪60年代后期开始减少,1986年发生了突变,之后迅速减少.流域内降水季节分配很不均匀,夏季降水最多,占年降水的55%,春、秋季均占年降水的21%,冬季占年降水的3%;春、夏季降水减少不显著,秋季降水减少显著,但进入本世纪,秋雨开始增多,冬季降水有不显著的增多趋势.中下游过度垦殖及河流源头过多的小水利工程等人类活动造成地表状况变化,降水有加剧减少的迹象;流域外大量调水虽然对降水不足有相当的补偿作用,但地表调水显然没有使流域内的天然降水量增加;地表植被增加和人类活动对地表影响较小的区域降水减少比较缓慢.     

长江流域梅雨期大范围持续性强降水事件的自维持机制:2020年一次暴雨过程的个例分析

长江流域梅雨期降水强度大、范围广、持续时间长,经常导致大范围严重洪涝灾害。该类强降水事件的内动力学过程值得深入讨论。本文以2020年7月5～9日长江流域一次大范围持续性降水为例,通过WRF数值试验分析了降水过程中的凝结潜热与环流系统的相互作用过程。结果表明:在此次大范围持续性强降水事件中,由于凝结潜热的释放,在高层形成高压异常,有利于南亚高压（SAH）加强东伸,SAH东伸的同时与西太平洋副热带高压（WPSH）相互作用,加强WPSH西伸。在潜热释放中心的中低层形成低压异常,有助于阻挡WPSH北上,从而形成稳定的WPSH,有利于降雨系统在长江流域的维持。东亚夏季风演变表现为明显的停滞与北跳特征,其中WPSH的活动是季风雨带演变的核心。本文研究表明,大尺度凝结潜热释放可以通过调节天气系统形成稳定的环流系统,从而有利于雨带加强和维持。这种大尺度雨带凝结潜热释放与环流的相互作用机制可能是夏季风雨带停滞的重要过程。     

全球升温1.5℃和2.0℃情景下澜沧江流域极端降水的变化特征

澜沧江是我国为数不多的跨境河流,流域内多发暴雨、洪水灾害,因此定量、科学地评估澜沧江流域未来全球升温情景下极端降水的变化特征,能够为澜沧江-湄公河沿线国家共同管理流域水资源和抵御自然灾害提供一定的科学指导。文中基于部门间影响模式比较计划（ISI-MIP）下5个全球气候模式降水数据,通过偏差校正增强其在澜沧江流域极端降水的模拟能力,使用降水强度、日最大降水量和强降水量等9个指标评价未来全球升温1.5℃和2.0℃下澜沧江流域极端降水的变化情况,并对结果的不确定性和可信度进行研究,得出以下主要结论：随着全球温度的升高,澜沧江流域年降水和极端降水均呈现增大趋势,其中极强降水量（R99p）升幅最大,升温1.5℃和2.0℃下升幅分别为37%和75%;相对于基准期,全球升温2.0℃下各极端降水指数增幅明显大于升温1.5℃,前者升幅甚至超出后者一倍;未来全球升温情景下,澜沧江流域湿季会变得更湿润,而干季则会更干燥;澜沧江流域降水集中程度会增大,使得流域内洪涝灾害发生的风险增大;ISI-MIP气候模式对澜沧江流域未来极端降水模拟存在较大不确定性,升温2.0℃较升温1.5℃情景下不确定性更大,但相对于基准期,前者极端降水增大的可信度更高。