Projected change in extreme rainfall events in China by the end of the 21st century using CMIP5 models

Projection of future climate changes and their regional impact is critical for long-term planning at the national and regional levels aimed at adaptation and mitigation. This study assesses the future changes in precipitation in China and the associated atmospheric circulation patterns using the Couple Model Intercomparison Project 5 Phase (CMIP5) simulations under the RCP4.5 and RCP8.5 scenarios. The results consistently indicate that the annual precipitation in China is projected to significantly increase at the end of the 21st century compared to the present-day levels. The number of days and the intensity of medium rain, large rain and heavy rain are obviously increased, while the number of trace rain days is projected to decrease over the entire area of China. Further analysis indicates that the significant increase of annual precipitation in Northwest China is primarily due to the increase of light rain and the increases in North and Northeast China are primarily due to the increase of medium rain. In the region of southern China, the increases of large rain and heavy rain play an important role in the increase of annual precipitation, while light rain events play a negative role. Analysis of the changes in atmospheric circulation indicates that the East Asian summer monsoon circulation is projected to be considerably stronger, and the local atmospheric stratification is projected to be more unstable, all of which provide a background benefit for the increase of precipitation and extreme rainfall events in China under global warming scenarios.     

Response of the East Asian climate system to water and heat changes of global frozen soil using NCAR CAM model

Under the condition of land-atmosphere heat and water conservation, a set of sensitive numerical experiments are set up to investigate the response of the East Asian climate system to global frozen soil change. This is done by introducing the supercooled soil water process into the Community Land Model (CLM3.0), which has been coupled to the National Center of Atmospheric Research Community Atmosphere Model (CAM3.1). Results show that:(1) The ratio between soil ice and soil water in CLM3.0 is clearly changed by the supercooled soil water process. Ground surface temperature and soil temperature are also affected. (2) The Eurasian (including East Asian) climate system is sensitive to changes of heat and water in frozen soil regions. In January, the Aleutian low sea level pressure circulation is strengthened, Ural blocking high at 500 hPa weakened, and East Asian trough weakened. In July, sea level pressure over the Aleutian Islands region is significantly reduced; there are negative anomalies of 500 hPa geopotential height over the East Asian mainland, and positive anomalies over the East Asian ocean. (3) In January, the southerly component of the 850 hPa wind field over East Asia increases, indicating a weakened winter monsoon. In July, cyclonic anomalies appear on the East Asian mainland while there are anticyclonic anomalies over the ocean, reflective of a strengthened east coast summer monsoon. (4) Summer rainfall in East Asia changed significantly, including substantial precipitation increase on the southern Qinghai-Tibet Plateau, central Yangtze River Basin, and northeast China. Summer rainfall significantly decreased in south China and Hainan Island, but slightly decreased in central and north China. Further analysis showed considerable upper air motion along ~30°N latitude, with substantial descent of air at its north and south sides. Warm and humid air from the Northeast Pacific converged with cold air from northern land areas, representing the main cause of the precipitation anomalies.     

华北夏季降水年代际变化与东亚夏季风、大气环流异常

利用华北夏季降水资料和NCEP/NCAR再分析资料,对华北夏季降水、东亚夏季风年代际变化特征及大气环流异常进行研究,发现一些有意义的结果:华北夏季降水变化存在明显的8a、18a周期,东亚夏季风变化18a、28a周期性比较明显,二者年代际变化特征明显,但华北夏季降水变化和东亚夏季风变化的周期不完全一致.华北夏季降水量变化在60年代中期发生了突变,东亚夏季风变化在70年代中期发生了突变.华北夏季降水与东亚夏季风变化存在很好的相关关系,强夏季风年,华北夏季降水一般偏多,弱夏季风年,华北夏季降水一般偏少,但又不完全一致.东亚夏季风减弱是造成华北夏季降水减少的一个重要因素,但不是唯一因素,华北夏季降水减少还与环流异常密切相关.在地面上,青臧高原地区、华北地区气温下降造成华北低压系统活动减少,不利于降水.在850 hPa层上,东亚中纬度的西南季风和副热带高压南部的偏东风、西北部的西南风异常减弱,使得西南气流输送水汽很多难以到达30°N以北的地区,而副热带高压西部外围偏东南、偏南气流输送到华北地区的水汽也大量减少,水汽不足造成华北夏季降水偏少.在500 hPa高度场上,80年代欧亚遥相关型表现与50年代相反,变为欧洲( )、乌拉尔山(-)、中亚( )形势,这种环流使得乌拉尔山高压脊减弱,贝加尔湖至青藏高原高空槽变浅,纬向环流表现突出,不利于冷暖空气南北交换.同时在500 hPa气温场上,80年代,西伯利亚至青藏高原西北部的冷槽明显东移南压到蒙古至华北地区,锋区位于华北以东以南位置,使得华北地区冷暖空气交汇减少,降水也因此减少.华北夏季降水减少是由于东亚夏季风减弱和大气环流异常造成的.     

Multiscale characteristics of the rainy season rainfall and interdecadal decaying of summer monsoon in North China

This paper focuses on the rainfall spectrum and its evolution of North China in rainy season with summer monsoon decaying in interdecadal time scale. The interannual component of the rainfall is the dominant part, accounting for 85% of the total variance, and has been changed significantly during the last 30 years. According to wavelet analysis its 5a periodic spectrum suddenly disappeared in the late 1960s, and its biennial oscillation gradually become weaker and weaker since 1970, accompanied by the summer monsoon decaying. Contrarily, the interdecadal component is principal in the summer monsoon over North China and is very similar to the counterpart of the rainfall. Their interdecadal parts are significantly correlated, and the correlation coefficient is nearly equal to the one of the original sequences.Besides, the dry and wet climate alternated with the monsoon abrupt changes in the 1960s and the 1970s over East Asia, apart from North China, climate drifted from a light drought to a severe drought during the past 30 years.     

East Asian monsoon change for the 21st century: Results of CMIP3 and CMIP5 models

Forty-two climate models participating in the Coupled Model Intercomparison Project Phases 3 and 5 were first evaluated in terms of their ability to simulate the present climatology of the East Asian winter (December-February) and summer (June-August) monsoons. The East Asian winter and summer monsoon changes over the 21st century were then projected using the results of 31 and 29 reliable climate models under the Special Report on Emissions Scenarios (SRES) mid-range A1B scenario or the Representative Concentration Pathways (RCP) mid-low-range RCP4.5 scenario, respectively. Results showed that the East Asian winter monsoon changes little over time as a whole relative to the reference period 1980-1999. Regionally, it weakens (strengthens) north (south) of about 25°N in East Asia, which results from atmospheric circulation changes over the western North Pacific and Northeast Asia owing to the weakening and northward shift of the Aleutian Low, and from decreased north- west-southeast thermal and sea level pressure differences across Northeast Asia. In summer, monsoon strengthens slightly in East China over the 21st century as a consequence of an increased land-sea thermal contrast between the East Asian continent and the adjacent western North Pacific and South China Sea.     

The spring soil moisture and the summer rainfall in eastern China

The relation between the soil moisture in spring and the rainfall in summer in eastern China is investi- gated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea tem- perature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.     

Interannual variation of North China rainfall in rainy season and SSTs in the equatorial eastern Pacific

The rainfall in North China during rainy season （July and August （JA）） exhibits a strong interannual variability. In this study, the atmospheric circulation and SST anomalies associated with the interannual variation of JA North China rainfall are examined. It is found that on the interannual timescale, the JA North China rainfall is associated with significant SST anomalies in the equatorial eastern Pacific, and the North China rainfall and SST anomaly in the equatorial eastern Pacific correspond to the similar variation of the upper-level westerly jet stream over East Asia. A possible mechanism is proposed for the influence of the SST anomalies in the equatorial eastern Pacific on the North China rainfall.     

Rainfall spectrum change in North China and its possible mechanism

The seasonal distribution of the rainfall in North China has changed greatly since 1977, with more rainfall in spring and less in July, August, and September (JAS). Wavelet analysis showed that the JAS rainfall underwent an abrupt spectrum change in the mid-1960s. Its interannual variability has declined while the interdecadal component has become the dominant mode, associated with the dry climate. Correlation analysis found that the JAS rainfall is negatively correlated with the departures of the 500 hPa geopotential height significantly over the northwest and southwest of China, and positively correlated with the suer monsoon over eastern China. Therefore, the interdecadal ascending of the air pressure in northwestern China and the monsoon decaying over East Asia in the past 20 years may be the two major causes of North China drought.     

ENSO对东亚夏季风和我国夏季降水的影响研究进展

回顾了最近几年我国学者在ENSO对东亚夏季风和我国夏季降水影响方面的研究成果,通过夏季风时降水的影响分析ENSO对夏季降水的作用,结合1997-1998年的ENSO现象,对前人的理论和统计结果进行了讨论,指出除了ENSO发生的时间、区域、强度外,其增长和衰减率在这一问题的研究中也值得关注。     

Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450?C1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pattern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400?C1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.     

Sensitivity experiments of impacts of large-scale urbanization in East China on East Asian winter monsoon

By using the global atmospheric general circulation model CAM4.0 including an urban canopy parameterization scheme,the possible impacts of large-scale urbanization in East China on East Asian winter monsoon was investigated via idealized numerical experiments.Results suggest that large-scale urbanization can cause a significant warming effect in both surface temperature and air temperature near the surface over most areas of East China.Meanwhile,large-scale urbanization also alters the surface energy balance,causing evident increases in net surface long-wave radiation and sensible heat flux as well as intensified surface thermal heating to the atmosphere.Forced by the surface thermal heating anomalies induced by the large-scale urban expansion,East Asian winter monsoon circulation exhibits distinct changes.Overall,the extensive urbanization over East China will weaken East Asian winter monsoon,but intensify winter monsoon in northeast China.     

Transition of the annual cycle of precipitation from double-peak mode to single-peak mode in South China

Previous studies revealed the double-peak mode (DPM) in South China precipitation, corresponding to the two stages in the rainy season, i.e. the first rainy stage (FRS) and the second rainy stage (SRS). But observations in recent two decades show that the DPM has changed to a single-peak mode (SPM). Both the precipitation amount and the heavy rainfall event frequency enhanced significantly in the gap between the FRS and the SRS in 1991–2010, compared to those in 1961-1990. This change can be linked to the effects of the global warming. During the warmer period, the July sea surface temperature over the western Pacific has greater increases than that over the central and eastern Pacific, especially west of 140°E. It may generate more tropical cyclones (TCs) in the inshore areas and then more typhoon rainfall over South China. On the other hand, the increments of the air temperature over the East Asian continent are greater than those of the SST over the western Pacific under the global warming, which enlarges the land-ocean temperature/pressure contrast and leads to a trend of the earlier onset dates of the Asian summer monsoon (ASM) in recent two decades. Then, the earlier ASM will facilitate the western Pacific subtropical high (WPSH) to retreat earlier from the South China Sea and enhance the convective precipitation in South China between the FRS and the SRS. Also, due to the warmer ocean, the WPSH locates more westward in July, and more moisture will be transported to South China from the southwest side to the WPSTH. All these influences favor a remarkably increasing precipitation in the gap in the warmer period and changes the seasonal cycle from double-peak mode to single-peak mode.     

中国西部绿化对东亚季风气候影响的数值模拟

中国西部大开发战略中的生态环境建设将在西部地区引起显著的地表覆盖变化。根据最新的全球地表特征数据库资料和21世纪初中国西部生态环境三大重点建设工程的具体规划，得出两种植被，即现实植被和虚拟植被。并利用RIEMS—TEA模式，通过一次敏感性试验，发现西部地区绿化明显影响东亚的季风系统和中国东部季风区气候。模拟试验显示，中国西部绿化会明显增强东亚夏季风，这将会加强中国东部由南向北的水汽输送，并有利于输送邻近海洋的水汽到大陆，使得中国大陆东部季风区整体出现降温、增湿和降水增加。而且，温度、湿度、气压和风速受影响的程度在垂直方向上都已超出了边界层之外。     

Linear relationship between the interdecadal and interannual variabilities of North China rainfall in rainy season

Interdecadai and interannuai timescales are dominant in the North China rainfall in rainy season (July and August). On the interdecadai timescale, the North China rainfall exhibited an abrupt decrease at the end of 1970s. In this study, we examined the effect of this abrupt rainfall decrease on the association between rainfall and circulation on the interannuai timescale, and found that the interdecadal variation does not change the physical mechanism responsible for the interannuai variation of North China rainfall.There is a linear relationship between the interdecadai and interannuai variabilities of North China rainfall in rainy season.     

用湿位涡定义的南海西南季风指数及其与我国区域降水的关系研究

使用美国NCEP／NCAR1958－1997年逐日资料,对南海季风爆发前后的气象要素场作了分析。结果表明：南海季风爆发时,南海南、北部要素场变化有差异,北部西南季风爆发特征更为显著。针对南海西南季风爆发特征,提出了用湿位势涡度定义季风指数,它能很好地反映夏季风爆发的特征。其中,用湿位热涡度定义的季风指数对长江中下及华北华南地区的旱涝具有一定的预示性。相关分析表明：前一年冬季的季风指数和秋季的季风指数分别与华北次年夏季降水、华南次年春季降水有显著的相关,而当年夏季的季风指数与长江中下游当年秋季降水呈显著正相关。     

青藏高原冬季积雪异常对东、南亚夏季风影响的初步数值模拟研究

利用一个耦合了简化的简单生物圈模式的大气环流谱模式（ＳＳｉＢ－ＧＣＭ），初步探讨了青藏高原冬季积雪异常对东、南亚夏季风环流和降水的影响及其机理。结果表明，高原地区冬季积雪增加将使随后的夏季东、南亚季风明显减弱，主要表现为东、南亚季风区降水减少，索马里急流、印度季风槽和印度西南气流减弱。另外，还提出欧亚大陆雪盖与整个高原雪盖和高原东部雪盖对东、南亚夏季风影响的敏感性问题。与欧亚大陆雪盖相比，高原雪盖是影响东、南亚季风的更敏感区，冬季高原以外雪盖增加，有可能使亚洲季风增强；当高原东部雪盖增加时，高原以东地区及印支半岛降水减少，印度东部、南部和孟加拉湾西北部降水反而增加     

Asian-Pacific Oscillation index and variation of East Asian summer monsoon over the past millennium

To study the long-term variation of the East Asian summer monsoon （EASM）, the Asian-Pacific Oscillation index （IAPO）, representing a zonal thermal contrast between Asia and the North Pacific, is reconstructed over the past millennium. During the Little Ice Age （LIA）, the variability of the reconstructed IAPO is closely linked to dry-wet anomalies in eastern China on the centennial scale. This correlation pattern is consistent with the observation during the current period, which suggests that the reconstructed IAPO may generally represent the centennial-scale variation of the EASM and rainfall anomalies over eastern China during the LIA.     

东亚夏季风异常的研究

本文运用经验正交函数分析方法,对10～65°N,90°E～175°W范围内近30年逐年7月和8月平均海平面气压场进行了分析研究.结果表明,第一、第三特征向量与东亚季风异常有关,第二特征向量与西风环流异常有关.讨论了东亚季风异常与大气环流的关系,以及季风异常对华北东部地区降水时空分布的影响.     

Study on response of ecosystem to the East Asian monsoon in eastern China using LAI data derived from remote sensing information

Based on the leaf area index (LAI) data derived from remote sensing information and eco-climate data, the responses of regional ecosystem variations in seasonal and interannual scales to the East Asian monsoon are studied. It is found that the vegetation ecosystems of eastern China are remarkably correlated with the East Asian monsoon in seasonal and interannual scales. In the seasonal timescale, the obvious variations of the vegetation ecosystems occur with the development of the East Asian monsoon from the south in the spring to the north in the autumn. In the interannual scale, high LAI appears in the strong East Asian monsoon year, whereas low LAI is related to the weak East Asian monsoon year. These further lead to the characteristic of "monsoon-driven ecosystem" in the eastern China monsoon region, which can be revealed by LAI.     

四川南部秋季降水变化及相应大气环流异常特征

利用1961—2014年全国756站的降水资料和美国NOAA-CIRES的20CR月平均再分析资料,研究了四川南部秋季(9～11月)降水变化及其相应的大气环流异常特征。结果表明,四川南部秋季降水具有显著的年际和年代际变化特征,其年际周期以2～4 a和准6 a为主,年代际周期以9～15 a为主。它与黄淮流域同期降水存在显著的负相关关系,与四川南部秋季降水关系密切的大气环流结构是北大西洋—俄罗斯西部—蒙古西部—东亚(NRMA)遥相关波列,NRMA遥相关波列在东亚地区激发出一个气旋性环流,与此同时,中南半岛西侧存在一个反气旋性环流,以上环流型有利于北方冷空气和来自孟加拉湾的暖湿气流在四川南部地区汇合,从而容易导致该地区降水的产生,反之亦然。