Future Changes of Drought and Flood Events in China under a Global Warming Scenario

This study investigates the impact of global warming on drought/flood patterns in China at the end of the 21st century based on the simulations of 22 global climate models and a regional climate model(RegCM3) under the SRES(Special Report on Emissions Scenarios) A1B scenario.The standardized precipitation index(SPI),which has well performance in monitoring the drought/flood characteristics(in terms of their intensity,duration,and spatial extent) in China,is used in this study.The projected results of 22 coupled models and the RegCM3 simulation are consistent.These models project a decrease in the frequency of droughts in most parts of northern China and a slight increase in the frequency in some parts of southern China.Considering China as a whole,the spatial extents of droughts are projected to be significantly reduced.In contrast,future flood events over most parts of China are projected to occur more frequently with stronger intensity and longer duration than those prevalent currently.Additionally,the spatial extents of flood events are projected to significantly increase.     

基于RegCM3的2006年中国南方夏季持续高温干旱天气的模拟研究

利用区域气候模式RegCM3并行版本,对2006年7—8月发生在中国南方的持续高温干旱气候事件进行了数值模拟试验。通过对模拟结果的对比分析,发现RegCM3能够较好地模拟出2006年夏季盘踞在中国大陆的副热带高压,同时模拟的暖区位置、范围及强度与实况也较接近。相关性检验结果也表明,RegCM3对发生在中国南方的持续高温天气具有一定的模拟能力。     

华北地区未来气候变化的高分辨率数值模拟

使用20km高水平分辨率的区域气候模式RegCM3,单向嵌套FvGCM/CCM3全球模式,进行了中国区域气候变化的数值模拟试验,分析华北地区夏半年4-9月的气温、降水和高温、干旱事件的变化。模式积分时间分为两个时段,分别为当代的1961-1990年和在IPCC SRES A2温室气体排放情景下的21世纪末2071-2100年。模式检验结果表明:在大部分月份,区域模式对当代气候的模拟都较全球模式更好。两个模式模拟的未来气温和降水变化,在空间分布型和量级上都有一定不同,如区域模式的升温更高,降水出现大范围减少等。此外,使用日最高气温不低于35℃的日数(D_(T35))和考虑了湿度因素的炎热指数(I_(H))不低于35℃的日数(D_(H135)),分析了区域模式模拟的未来高温事件变化,结果表明:未来华北地区D_(T35)和平原地区D_(H135)均有较大增加。未来华北地区的连续干旱日数(CDD)将增加,依照UNEP(United Nations Environment Programme)干旱指数(A_(U))给出的气候湿润区将有较大幅度减少,而半湿润半干旱区和半干旱区面积将增加。     

RegCM4对华北区域21世纪气候变化预估研究

利用国家气候中心完成的RegCM4区域气候模式在RCP4.5和RCP8.5两种排放路径下的气候变化动力降尺度试验结果,在检验模式对基准期(1986—2005年)气温和降水模拟能力基础上,进行华北区域21世纪气候变化预估分析。结果表明：RegCM4对华北区域基准期气温和降水的模拟能力较好。未来21世纪,两种情景下华北区域气温、降水、持续干期(consecutive dry days, CDD)和强降水量(R95p)变化逐渐增大,但变化幅度在高排放的RCP8.5情景下更为显著,其中近期(2021—2035年)、中期(2046—2065年)、远期(2080—2098年)RCP8.5情景下年平均气温分别升高1.77、3.44、5.82℃,年平均降水分别增加8.1%、14%、19.3%,CDD分别减少3、3、12 d, R95p分别增加30.8%、41.9%、69.8%。空间上,未来21世纪华北区域内年、冬季、夏季平均气温将一致升高,夏季升温幅度最大;年、冬季、夏季平均降水整体以增加为主,冬季降水增加幅度最大;CDD以减少为主,但近期和中期在山西和京津冀有所增加,而R95p以增加为主,表明21世...     

中国干湿变化的高分辨率区域气候模式预估

本文使用三个全球气候模式驱动下的高分辨率区域气候模式RegCM4的试验数据,首先评估了RegCM4对参考时段（1986～2005年）中国干燥度指数（AI）的模拟能力,而后根据典型浓度路径中等排放（RCP4.5）情景下RegCM4试验对中国未来干湿变化进行了预估研究。结果表明,RegCM4能够合理模拟中国区域AI的空间分布。两种潜在蒸散发计算方法得到的参考时段AI在空间分布和数值上存在一定差异,尤其是在中国西部高海拔地区和北方地区。在三个全球气候模式驱动场作用下的RegCM4预估试验中,21世纪中期（2046～2065年）和末期（2081～2098年）中国区域平均AI较参考时段分别减小2%～4%和2%～5%,其中西北中部变湿,其他地区均变干。不同地区未来干湿变化的主要影响因素存在差异,西北中部降水变化为主导因素,其他地区主要受控于升温所引起的潜在蒸散发变化。     

Near future (2016-40) summer precipitation changes over China as projected by a regional climate model (RCM) under the RCP8.5 emissions scenario: Comparison between RCM downscaling and the driving GCM

Multi-decadal high resolution simulations over the CORDEX East Asia domain were performed with the regional climate model RegCM3 nested within the Flexible Global Ocean-Atmosphere-Land System model, Grid-point Version 2 (FGOALS-g2). Two sets of simulations were conducted at the resolution of 50 km, one for present day (1980–2005) and another for near-future climate (2015–40) under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Results show that RegCM3 adds value with respect to FGOALS-g2 in simulating the spatial patterns of summer total and extreme precipitation over China for present day climate. The major deficiency is that RegCM3 underestimates both total and extreme precipitation over the Yangtze River valley. The potential changes in total and extreme precipitation over China in summer under the RCP8.5 scenario were analyzed. Both RegCM3 and FGOALS-g2 results show that total and extreme precipitation tend to increase over northeastern China and the Tibetan Plateau, but tend to decrease over southeastern China. In both RegCM3 and FGOALS-g2, the change in extreme precipitation is weaker than that for total precipitation. RegCM3 projects much stronger amplitude of total and extreme precipitation changes and provides more regional-scale features than FGOALS-g2. A large uncertainty is found over the Yangtze River valley, where RegCM3 and FGOALS-g2 project opposite signs in terms of precipitation changes. The projected change of vertically integrated water vapor flux convergence generally follows the changes in total and extreme precipitation in both RegCM3 and FGOALS-g2, while the amplitude of change is stronger in RegCM3. Results suggest that the spatial pattern of projected precipitation changes may be more affected by the changes in water vapor flux convergence, rather than moisture content itself.     

Spatiotemporal characteristics of regional drought occurrence in East Asia

Droughts in the East Asian region (105–150°E, 20–50°N) are quantified using the effective drought index (EDI) over a period of 43 years, from 1962 to 2004, and the East Asian region was classified into six subregions on the basis of similarity in drought climate: (D1) South China; (D2) lower region of the Yangtze River, South Korea, and Central/South Japan; (D3) Central China and North Korea; (D4) Northwest China and middle region of the Yangtze River; (D5) North China; and (D6) Northeast China and North Japan. The EDI time series was then summarized for the different drought subregions and a drought map was created that shows the spatiotemporal characteristics of regional drought occurrence in East Asia. The map shows that in subregions, D1, D2, D3, D4, D5, and D6, there were 50 (11.63 per decade), 36 (8.37 per decade), 30 (6.98 per decade), 28 (6.51 per decade), 29 (6.74 per decade), and 33 (7.67 per decade) drought occurrences, respectively. The most common characteristic of droughts in the subregions is that short-term droughts (<200 days) which mainly occur in spring and summer, whereas long-term droughts (≥200 days) mainly occur in autumn and winter. D1 shows the highest frequency of short-term droughts. Short-term droughts occur more frequently than long-term droughts in D2 and D3, but D4 and D6 showed a higher frequency of long-term droughts than short-term droughts. D5 showed a similar frequency of short- and long-term droughts. Drought onset dates are evenly distributed throughout the year for D1, D2, and D3, but distributed mostly in spring and summer in D4, D5, and D6. All the differences are linked to variations in the precipitation cycle of each subregion. In terms of annual variations in drought occurrence, D2 showed weakening droughts (the annual lowest EDI shows a positive trend), whereas the other subregions showed intensifying droughts (the annual lowest EDI shows a negative trend). The greatest intensifying trend was observed in D5, followed by D3, D6, D4, and D1.     

全球和区域气候模式对中国东部夏季降水季节演变模拟的比较

本文利用全球海气耦合模式(MIRO3.2_hires)和区域气候模式(RegCM3)的模拟结果,分析了东亚地区夏季降水和大气环流的季节演变特征,并与NCEP/DOE再分析资料和降水观测资料进行了对比分析.结果表明,全球和区域气候模式都能反映出中国东部地区夏季平均环流场和降水场气候态分布的基本特征,但全球模式模拟的雨带范...     

RegCM3 CORDEX东亚试验模拟和预估的中国夏季温度变化

按照CORDEX (COordinated Regional Downscaling Experiment) 计划试验设计要求,利用中国科学院大气物理研究所全球模式FGOALS-g2的数据驱动区域气候模式RegCM3,针对1986~2005年历史气候和2010~2065年RCP8.5排放情景下气候预估,对东亚地区进行了50 km动力降尺度模拟。首先评估了RegCM3模式及驱动模式FGOALS-g2对1986~2005年夏季中国地表气温和极端高温事件的模拟能力,然后比较了两个模式在RCP8.5排放情景下对中国夏季地表气温和极端高温事件预估的变化,重点分析了动力降尺度结果的优势。结果表明,两个模式均能合理再现夏季中国地表气温和极端高温事件的大尺度气候态特征。相对于全球模式,区域模式由于水平分辨率较高,能在刻画地表气温分布的细节上体现出优势。在RCP8.5排放情景下,两个模式预估的三个地表气温指标均显著升高,到21世纪中期 (2046~2065年),两个模式预估的全国平均地表气温增幅相当,气温日较差变化均较小。在FGOALS-g2模式预估中,到21世纪中期,三个地表气温指标的增幅相当,气温日较差没有明显变化,东北和青藏高原的地表气温增幅最大。在RegCM3模式预估中,到21世纪中期,中国大部分地区日最高气温 (Tmax) 增幅大于日最低气温 (Tmin) 增幅,气温日较差增加;而在青藏高原西部,Tmax的增幅较Tmin偏低,气温日较差减小。在RCP8.5排放情景下,两个模式预估的极端高温事件到21世纪中期也显著增加,RegCM3模式预估的极端高温事件全国平均增幅略高于FGOALS-g2模式的预估。在两个模式的预估中,日最高气温最大值 (TXx)、暖昼指数 (TX90p) 和持续暖期指数 (WSDI) 变化的空间分布特征与Tmax相似;和当代相比TX90p增加了60%以上,而WSDI增加了一倍以上。     

SIMULATION OF SUMMER CLIMATE IN CHINA DURING 1997 AND 1998 USING A REGIONAL AIR-SEA COUPLED MODEL

Using the regional air-sea coupled climate model RegCM3-POM,a series of numerical experiments are performed to simulate the summer climate in 1997 and 1998 with different coupling time steps.The results show that the coupled model has good performance on the simulation of the summer sea surface temperature(SST) in 1997 and 1998,and the simulation results of CPL1(with the coupling time step at 1 hour) are similar to those of CPL6(with the coupling time step at 6 hours).The coupled model can well simulate SST differences between 1997 and 1998.As for the simulation of the drought in 1997 and the flood in 1998,the results of CPL6 are more accurate.The coupled model can well simulate the drought in 1997 over North China,and compared with the results of the atmosphere model RegCM3,the simulation ability of the coupled model is improved.The coupling model has better ability in the simulation of the circulation in the middle and low levels,and the water vapor transportation in the coupling model is reasonable in both 1997 and 1998.RegCM3(an uncoupled model) cannot correctly simulate the transportation path differences between 1997 and 1998,but the coupled model can simulate the differences well.     

区域气候模式对温室效应引起的中国地区气候变化的数值模拟

利用基于 ＲｅｇＣＭ２的区域气候模式并单向嵌套澳大利亚 ＣＳＩＲＯ Ｒ２１Ｌ９全球海－气耦合模式，进行了温室气体二氧化碳浓度倍增对中国气候变化影响的数值试验研究。控制试验结果表明：区域模式由于具有较高的分辨率，因而对中国区域地面气温和降水的模拟效果较全球模式有了较大提高；模式对 ２×ＣＯ２敏感性试验结果表明了在 ＣＯ２浓度倍增情况下，由于温室效应，中国区域的地面气温将有明显升高，降水也将呈增加趋势。     

土地利用变化对长江流域气候及水文过程影响的敏感性研究

使用区域气候模式(RegCM3)和大尺度汇流模型(LRM), 研究土地利用/植被覆盖变化对长江流域气候及水文过程的影响。RegCM3嵌套于欧洲数值预报中心 (ECMWF) 再分析资料ERA40, 分别进行了中国区域在实际植被和理想植被分布情况下两个各15年 (1987～2001年) 时间长度的积分试验。随后, RegCM3 两个试验的输出径流结果分别用来驱动LRM, 研究土地利用/植被覆盖变化对长江流域河川径流的影响。研究结果指出, 中国当代土地利用变化对长江流域降水、蒸散发、径流深及河川径流等水文气候要素的改变较大, 对气温的改变并不明显。土地利用变化引起长江干流河川径流量在夏季(6～8月)有所增加, 并且越向下游增加幅度越大, 其中大通站径流量增加接近15%。总体而言, 土地利用改变加剧了长江流域夏季水循环过程, 使得夏季长江中下游地区降水增多, 径流增大。     

中国当代土地利用变化对黄河流域径流影响

使用区域气候模式(RegCM3)和大尺度汇流模型(LRM),研究中国地区土地利用/植被覆盖变化对黄河流域降雨径流过程的影响。RegCM3嵌套于欧洲数值预报中心(ECMWF)再分析资料ERA40,分别进行了中国区域在实际植被和理想植被分布情况下两个各15年(1987～2001年)时间长度的积分试验。随后,RegCM3 两个试验的输出径流结果分别用来驱动LRM。与观测资料的对比分析表明,在实际土地利用状况下,LRM能较好地模拟黄河河川径流的季节和年际变化。研究结果指出,当代土地利用引起了冬季黄河上游部分地区降水减少,中下游地区降水增加;引起夏季整个黄河流域降水的减少。总体来说,当代土地利用变化引起黄河流域年平均降水的减少。对于水文站河川径流量,除了冬春季略有增加外,其他月份河川径流均会减少,并且在9月减少最多。土地利用引起的植被退化造成黄河径流的大幅度减少,并且越向下游减少幅度越大,这可能是引起黄河下游断流的重要原因之一。     

温室效应对我国东部地区气候影响的高分辨率数值试验

使用RegCM3区域气候模式,单向嵌套NASA/NCAR 的全球环流模式FvGCM的输出结果,对中国东部地区进行了在实际温室气体浓度下当代1961~1990年和在IPCC A2温室气体排放情景下21世纪末期2071~2100年各30年时间长度,水平分辨率为20 km的气候变化模拟试验。首先分析全球和区域模式对中国东部地区当代气候的模拟情况,结果表明全球模式对中国东部地区气温的总体分布型模拟较好,但存在冷偏差,区域模式在对这个冷偏差有所纠正的同时,提供了气温地理分布更详细的信息。全球模式模拟的年降水中心位于长江流域,与观测差别较大,区域模式对此同样也有改进,降水高值区主要位于区域南部,并表现出较强的地形强迫特征。区域模式的模拟结果还表明,至21世纪末期,在温室效应作用下,中国东部的气温将明显升高,年平均气温的升高值在2.7~4.0℃之间,其中北部升温大于南部,冬季升温大于夏季。冬季升温表现出明显的随纬度增加而增加的分布型。模拟区域内年平均降水将增加,增加值一般在10%以上,部分地区达到30%。降水增加在夏季较明显,区域内以普遍增加为主,冬季降水自山东半岛至湖南地区将减少,其他地区增加。此外,对夏季高温日数和冬季低温日数及年平均大雨日数的变化也进行了分析。     

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.     

Simulation of China Summer Precipitation Using a Regional Air-Sea Coupled Model

A regional air-sea coupled model based on the regional climate model(RegCM3)and the regional oceanic model POM(Princeton Ocean Model)is developed and a series of experiments are performed to verify the ability of the coupled model in simulating the summer precipitation over China from 1963 to 2002.The results show that the space correlation coefficients between the GISST(Global Ice and Sea Surface Temperature)data and the simulated SST by RegCM3-POM exceed 0.9.Compared with the uncoupled experiments,the coupled model RegCM3-POM has a better performance in simulating the mean summer(June to August)precipitation over China,and the distribution of the rainband in the coupled model is more accurate.The improvement of the rainfall simulation is significant over the Yangtze River Valley and in South China.The rainbelt intraseasoaal evolution over eastern China in summer indicates that the simulation ability of RegCM3-POM is improved in comparison with the uncoupled model.The interannual summer rainfall variation over eastern China simulated by RegCM3-POM is in accordance with observation,while the spatial pattern of the interannual summer rainfall variation in the uncoupled model is inaccurate.The simulated correlation coefficient between the summer rainfall in the uncoupled model RegCM3 and observation is0.30 over the Yangtze River Valley and 0.29 in South China.The coefficient between the rainfall in the coupled RegCM3-POM and observation is 0.48 over the Yangtze River Valley and 0.61 in South China.The RegCM3-POM has successfully simulated the correlation coefficients between summer rainfall in the Yangtze River Valley and SST anomalies of the Bay of Bengal,South China Sea,and the Kuroshio area,whereas the uncoupled model RegCM3 fails to reproduce this relationship.The study further shows that the monsoon circulation and the path of the moisture transport flux simulated by RegCM3-POM are in good agreement with the NCEP/NCAR data.     

水汽输送对中国东部夏季雨带变化影响的诊断模拟

运用SVD方法分析了水汽输送与中国东部夏季降水的关系,结果表明:南海水汽输送通量的增加,一般使华南及江南地区的降水增强;孟加拉湾关键区水汽输送通量的增加,一般使华南和江南地区的降水增强,而使江淮流域的降水减弱。运用区域气候模式RegCM3,通过改变南海与孟加拉湾2个关键区水汽输送通量的敏感性试验,发现关键区水汽输送的变化,基本不改变主雨带的分布形势,但会对局部区域的降水产生影响。这基本验证了诊断分析的结果。     

区域气候模式在不同分辨率下对西北太平洋热带气旋生成气候特征的比较研究

利用RegCM3区域气候模式,试验研究了15、30、45和60 km 4个分辨率下西北太平洋热带气旋的生成特征.结果表明,RegCM3模式对西北太平洋热带气旋生成的模拟能力受分辨率的影响.分辨率的简单提高,并不一定会使模式的模拟能力有所改善.模式在30 km分辨率下对西北太平洋热带气旋生成频数及频数变化的模拟能力最强,在60 km分辨率下对西北太平洋热带气旋生成频数空间分布的模拟能力最强,在15 km分辨率下对西北太平洋热带气旋生成频数、频数空间分布及频数变化的模拟能力最弱.对比分析不同分辨率下热带气旋的生成过程表明,热带气旋生成前期,β中尺度涡旋没有发生合并,对流层中低层水汽含量不足是导致模式在15 km分辨率下模拟热带气旋生成频数较差的主要原因.     

基于蒸散干旱指数的华北地区干旱研究

本文利用卫星遥感资料以及常规气象资料驱动基于地表净辐射、植被指数、平均气温和日温差的蒸散模型来估测日实际蒸散量,并与栾城站涡动相关法测量的实际蒸散作对比验证。定性分析了实际蒸散与各相关影响因子的时空变化规律;通过蒸散干旱指数（EDI）分析华北地区的干旱分布特点,并分别与PDSI指数和降水距平百分率作对比。结果表明：ET模型估测的蒸散值与实测值的相关性很好,其模拟精度对于大面积干旱监测的空间尺度上是可用的;EDI距平指数表征干旱分布的空间分辨率较高,且对旱情的指示和干旱程度的判定比较可靠。     

区域海气耦合模式对中国夏季降水的模拟

以区域气候模式RegCM3和普林斯顿海洋模式POM为基础,建立了一个区域海气耦合模式,对1963-2002年中国夏季气候进行模拟,重点分析该耦合模式对中国夏季降水的模拟性能以及降水模拟改进的可能原因.结果表明:耦合模式对中国夏季雨带分布的模拟明显优于控制试验(单独的大气模式),对长江流域以及华南降水的模拟性能改进尤为明显,同时耦合模式能够更为真实地刻画中国东部地区汛期雨带的移动.对降水的年际变化分析发现,耦合模式模拟的1963-2002年中国夏季降水年际变率与观测吻合,模拟的夏季长江流域降水与观测降水相关系数达到0.48,模拟的华南夏季降水与观测的相关系数达到0.61,而控制试验结果与观测降水的相关系数均较小.对中国东部长江流域夏季降水与近海海温的相关分析表明,用给定海温驱动的大气模式,并不能正确模拟出中国东部夏季降水与海温的关系,而耦合模式能够较好地模拟出长江流域与孟加拉湾、南海以及黑潮区海温的关系,与GISST(全球海冰和海表温度)和观测降水相关关系一致.对水汽输送通量的分析发现,控制试验模拟的水汽输送路径与NCEP/NCAR再分析资料相比差别较大,耦合模式模拟的来自海洋上的水汽输送强度和路径与NCEP/NCAR再分析资料一致,提高了耦合模式对水汽输送的模拟能力,从而改善了模式对华南以及长江流域降水的模拟.