The Impact of Atmospheric Heat Sources over the Eastern Tibetan Plateau and the Tropical Western Pacific on the Summer Rainfall over the Yangtze-River Basin

The variability of the summer rainfall over China is analyzed using the EOF procedure with a new parameter （namely, mode station variance percentage） based on 1951-2000 summer rainfall data from 160 stations in China. Compared with mode variance friction, the mode station variance percentage not only reveals more localized characteristics of the variability of the summer rainfall, but also helps to distinguish the regions with a high degree of dominant EOF modes representing the analyzed observational variable. The atmospheric circulation diagnostic studies with the NCEP/NCAR reanalysis daily data from 1966 to 2000 show that in summer, abundant （scarce） rainfall in the belt-area from the upper-middle reaches of the Yangtze River northeastward to the Huaihe River basin is linked to strong （weak） heat sources over the eastern Tibetan Plateau, while the abundant （scarce） rainfall in the area to the south of the middle-lower reaches of the Yangtze River is closely linked to the weak （strong） heat sources over the tropical western Pacific.

The Linkage between Two Types of El Ni?o Events and Summer Streamflow over the Yellow and Yangtze River Basins

It is generally agreed that El Nino can be classified into East Pacific(EP)and Central Pacific(CP)types.Nevertheless,little is known about the relationship between these two types of El Ni?o and land surface climate elements.This study investigates the linkage between EP/CP El Ni?o and summer streamflow over the Yellow and Yangtze River basins and their possible mechanisms.Over the Yellow River basin,the anomalous streamflow always manifests as positive(negative)in EP(CP)years,with a correlation coefficient of 0.39(-0.37);while over the Yangtze River basin,the anomalous streamflow shows as positive in both EP and CP years,with correlation coefficients of 0.72 and 0.48,respectively.Analyses of the surface hydrological cycle indicate that the streamflow is more influenced by local evapotranspiration(ET)than precipitation over the Yellow River basin,while it is dominantly affected by precipitation over the Yangtze River basin.The different features over these two river basins can be explained by the anomalous atmospheric circulation,which is cyclonic(anticyclonic)north(south)of 30°N over East Asia.EP years are dominated by two anticyclones,which bring strong water vapor convergence and induce more precipitation but less ET,and subsequently increase streamflow and flooding risks.In CP years,especially over the Yellow River basin,two cyclones dominate and lead to water vapor divergence and reduce moisture arriving.Meanwhile,the ET enhances mainly due to local high surface air temperature,which further evaporates water from the soil.As a result,the streamflow decreases,which will then increase the drought risk.

Predicting June Mean Rainfall in the Middle/Lower Yangtze River Basin

We demonstrate that there is significant skill in the GloSea5 operational seasonal forecasting system for predicting June mean rainfall in the middle/lower Yangtze River basin up to four months in advance.Much of the rainfall in this region during June is contributed by the mei-yu rain band.We find that similar skill exists for predicting the East Asian summer monsoon index(EASMI)on monthly time scales,and that the latter could be used as a proxy to predict the regional rainfall.However,there appears to be little to be gained from using the predicted EASMI as a proxy for regional rainfall on monthly time scales compared with predicting the rainfall directly.Although interannual variability of the June mean rainfall is affected by synoptic and intraseasonal variations,which may be inherently unpredictable on the seasonal forecasting time scale,the major influence of equatorial Pacific sea surface temperatures from the preceding winter on the June mean rainfall is captured by the model through their influence on the western North Pacific subtropical high.The ability to predict the June mean rainfall in the middle and lower Yangtze River basin at a lead time of up to 4 months suggests the potential for providing early information to contingency planners on the availability of water during the summer season.

Dominant variation modes associated with Yangtze–Huai River Basin summer heavy rainfall events

The Yangtze–Huai River Basin(YHRB)always suffers from anomalously heavy rainfall during the warm season,and has been well explored as a whole area during the past several decades.In this study,the YHRB is divided into two core regions-the northern YHRB(nYHRB)and southern YHRB(sYHRB)-based on 29-year(1979–2007)June–July–August(JJA)temporally averaged daily rainfall rates and the standard deviation of rainfall.A spectral analysis of JJA daily rainfall data over these 29 years reveals that a 3–7-day synoptic-timescale high-frequency mode is absolutely dominant over the nYHRB,with 10–20-day and 15–40-day modes playing a secondary role.By contrast,3–7-day and 10–20-day modes are both significant over the sYHRB,with 7–14-day,15–40-day,and 20–60-day modes playing secondary roles.Based on a comparison between bandpass-filtered rainfall anomalies and original rainfall series,a total of 42,1,5,and 3 heavy rainfall events(daily rainfall amounts in the top 5%of rainy days)are detected over the nYHRB,corresponding to 3–7-day,7–14-day,10–20-day,and 15–40-day variation disturbances.Meanwhile,a total of 28,8,12,and 6 heavy rainfall events are detected over the sYHRB,corresponding to 3–7-day,7–14-day,10–20-day,and 20–60-day variation disturbances.The results have important implications for understanding the duration of summer heavy rainfall events over both regions.

Seasonal Rainfall Forecasts for the Yangtze River Basin of China in Summer 2019 from an Improved Climate Service

Rainfall forecasts for the summer monsoon season in the Yangtze River basin(YRB) allow decision-makers to plan for possible flooding, which can affect the lives and livelihoods of millions of people. A trial climate service was developed in 2016, producing a prototype seasonal forecast product for use by stakeholders in the region, based on rainfall forecasts directly from a dynamical model. Here, we describe an improved service based on a simple statistical downscaling approach. Through using dynamical forecast of an East Asian summer monsoon(EASM) index, seasonal mean rainfall for the upper and middle/lower reaches of YRB can be forecast separately by use of the statistical downscaling, with significant skills for lead times of up to at least three months. The skill in different sub-basin regions of YRB varies with the target season. The rainfall forecast skill in the middle/lower reaches of YRB is significant in May–June–July(MJJ), and the forecast skill for rainfall in the upper reaches of YRB is significant in June–July–August(JJA). The mean rainfall for the basin as a whole can be skillfully forecast in both MJJ and JJA. The forecasts issued in 2019 gave good guidance for the enhanced rainfall in the MJJ period and the near-average conditions in JJA. Initial feedback from users in the basin suggests that the improved forecasts better meet their needs and will enable more robust decision-making.

黄河流域生态保护迈向高质量发展的特征——植被绿度、生产力和降水利用效率的差异性变化

Globally,vegetation has been changing dramatically.The vegetation-water dynamic is key to understanding ecosystem structure and functioning in water-limited ecosystems.Continual satellite monitoring has detected global vegetation greening.However,a vegetation greenness increase does not mean that ecosystem functions increase.The intricate interplays resulting from the relationships between vegetation and precipitation must be more adequately comprehended.In this study,satellite data,for example,leaf area index(LAI),net primary production(NPP),and rainfall use efficiency(RUE),were used to quantify vegetation dynamics and their relationship with rainfall in different reaches of the Yellow River Basin(YRB).A sequential regression method was used to detect trends of NPP sensitivity to rainfall.The results showed that 34.53%of the YRB exhibited a significant greening trend since 2000.Among them,20.54%,53.37%,and 16.73%of upper,middle,and lower reach areas showed a significant positive trend,respectively.NPP showed a similar trend to LAI in the YRB upper,middle,and lower reaches.A notable difference was noted in the distributions and trends of RUE across the upper,middle,and lower reaches.Moreover,there were significant trends in vegetation-rainfall sensitivity in 16.86%of the YRB’s middle reaches—14.08%showed negative trends and 2.78%positive trends.A total of 8.41%of the YRB exhibited a marked increase in LAI,NPP,and RUE.Subsequently,strategic locations reliant on the correlation between vegetation and rainfall were identified and designated for restoration planning purposes to propose future ecological restoration efforts.Our analysis indicates that the middle reach of the YRB exhibited the most significant variation in vegetation greenness and productivity.The present study underscores the significance of examining the correlation between vegetation and rainfall within the context of the high-quality development strategy of the YRB.The outcomes of our analysis and the proposed ecological restoration framework can provide decision-makers with valuable insights for executing rational basin pattern optimization and sustainable management.

The Relationship Between June Precipitation over Mid-Lower Reaches of the Yangtze River Basin and Spring Soil Moisture over the East Asian Monsoon Region

Using the US Climate Prediction Center （CPC） soil moisture dataset and the observed precipitation over China together with the NCEP/NCAR reanalysis wind and air temperature, the relationship between June precipitation over mid-lower reaches of the Yangtze River basin （MLR-YRB） and spring soil moisture over the East Asian monsoon region was explored, with the signal of the ENSO effect on precipitation removed. A significant positive correlation was found between the mean June precipitation and the preceding soil moisture over the MRL-YRB. The possible response mechanism for this relationship was also investigated. It is found that when the soil over the MRL-YRB is wetter （drier） than normal in April and May, the air temperature in the lower troposphere over this region in May is lower （higher） than normal, and this temperature effect leads to a decrease （increase） in the temperature contrast between the land and the sea. Generally, a decrease （increase） in the land-sea temperature contrast leads to weaker （stronger） East Asian summer monsoon in June. Southerly （northerly） wind anomalies at 850 hPa then show up in the south of the Yangtze River basin while northerly （southerly） wind anomalies dominate in the north. These anomalies lead to the convergence （divergence） of wind and water vapor and hence gives rise to more （less） precipitation in June over the MLR-YRB.

青海黄河流域泥石流空间格局和趋势预估

为揭示青海黄河流域泥石流空间格局和易发性变化趋势,利用耦合地理探测器的信息量模型量化控制因子对研究区泥石流的空间解释力和不同极端降雨情景下泥石流的易发性。研究结果表明:泥沙连通度、大于10 mm降雨日数、连续3日最大降雨量和地层岩性是决定泥石流空间格局的关键因子。当前情景下泥石流极高和高易发区主要集中在东北部和中部的陡峭山区;极端降雨情境下,极高和高易发性的新增区域主要集中在北部、南部山地以及中部的阿尼玛卿雪山两侧。研究结果可为该地区的泥石流防灾减灾工作提供参考。

黄河流域降水序列变化的小波分析

采用1961-2000年黄河流域97个气象站点的系列资料，在分析黄河流域降水空间变化格局的基础上，采用墨西哥帽小波函数，对黄河流域近40a来降水的季节变化和年际变化时间序列进行了小波分析，揭示了黄河流域降水变化的多时间尺度的复杂结构，分析了不同时间尺度下降水序列变化的周期和突变点，并确定了各序列中存在的主要周期。结果表明：黄河流域多年平均降水量的地区分布既受天气系统的制约，又受地形等地理环境的影响，造成明显的地区性差异；黄河流域年降水和各季节降水均存在8～12a左右时问尺度的多少交替，表现出明显的周期特征，其次4～6a左右时间尺度的周期特征也较明显，夏季降水和年降水变化趋势具有较大相似性，不同时间尺度的周期特征之间有不同程度的吻合，说明夏季降水较大程度地控制着年降水。小波分析的时频局部化特性可展现降水时间序列的精细结构，为分析气候多时间尺度变化特征及短期气候预测等节水关键问题研究提供了一种新途径。

黄河流域植被覆盖度动态变化与降水的关系

利用８ｋｍ分辨率Ｐａｔｈｆｉｎｄｅｒ ＮＯＡＡ－ＮＤＶＩ数据，对黄河流域１９８２～１９９９年地表植被覆盖的空问分布及时间序列变化进行了分析，并通过计算不同时段降水量与年最大ＮＤＶＩ之间的相关系数分析了降水对流域植被覆盖的影响。结果发现近２０年来黄河流域平均植被覆盖度有增加趋势，但青藏高原上有所减小；汛期降水量的多少对地表植被覆盖度的年际变化起主要作用，其中草原地区影响最显著，而在森林植被区及部分灌溉农作区，降水的年际变化对地表覆盖的影响比较小。

近50年来黄河流域400mm等雨量线空间变化研究

以黄河流域及周边地区1026个雨量(水文)站1956—2000年逐日降水过程资料为基础,以GIS技术为关键数据处理平台,建立等值线加权平均位置的定量化表征方法,采用时间序列分析技术,对黄河流域近50年来400mm等雨量线的空间位移特征进行了系统揭示。1956—2000年间,黄河流域多年平均降雨量为454.62mm;400mm等雨量线加权平均位置坐标为(105°0′4″E,36°57′54″N)。整体上看,近50年来,黄河流域400mm等雨量在纬向上的移动是典型的平稳随机序列过程;在经向上的移动尚不能满足平稳随机序列过程。趋势检验结果表明,黄河流域400mm等雨量线有向东和向南发生移动的趋势,且向东移动的趋势显著。功率谱分析表明,黄河流域400mm等雨量线在经向上发生迁移的显著周期为3年;在经向和纬向上均有7年和2年周期;同时,位移具有反向持久性。

2003年夏季中高纬度环流与淮河流域降水

研究了 2 0 0 3年夏季中高纬环流特征以及乌拉尔山、鄂霍茨克海和贝加尔湖三个地区阻高指数逐候的变化情况。 6月下旬至 7月上旬东亚中高纬出现“双阻”形势 ,造成淮河流域持续一个多月的集中强降水 ,但是在 7月底 ,鄂霍次克海阻高再度建立并持续 ,致使盛夏西太平洋副热带高压较常年偏南 ,所以雨带的位置也未能北移。因此 2 0 0

黄河流域水文气象要素变化及与东亚夏季风的关系

为研究黄河流域水文气象要素变化规律,并揭示各要素与东亚夏季风之间的潜在关系,建立了全流域VIC水文模型、MK突变检验和MK相关检验。结果表明:从20世纪80年代中期开始,流域绝大部分地区气温上升趋势明显,而降水、蒸散发、径流深和土壤湿度呈整体减小趋势,且中游地区减幅最大。各要素与东亚夏季风相关密切,但空间差异性明显。气温与东亚夏季风强度普遍呈负相关,且宁蒙河段及内流区相关性显著;其他要素则相反,正相关显著区域主要位于河口镇到三门峡区间。研究还发现相比较降水,黄土高原径流深对夏季风强度变化更为敏感。因此,对东亚夏季风的研究可为预测黄河流域内水文过程及水资源的变化提供重要的科学参考。

近50年黄河流域夏季降水的时空变化及其与东亚副热带西风急流的关系

基于1959-2008年黄河流域92个测站降水量和NCEP/NCAR再分析资料,研究黄河流域夏季降水的时空变化和周期特征,及其与东亚副热带西风急流的关系。结果表明,黄河流域夏季降水呈现由东南向西北逐渐减少的分布特点,其夏季降水的异常空间型主要有3种:全流域一致型,东南多(少)西北少(多)型,西南多(少)东北少(多)型。当夏季东亚副热带西风急流中心异常偏北(南)时,同期黄河流域中上游地区降水偏多(少),下游降水偏少(多);东亚副热带西风急流中心异常偏东(西)时,黄河流域上游降水偏多(少),中下游地区降水偏少(多)。

厄尔尼诺/拉尼娜与淮河流域汛期降水年际关系的稳定性分析

根据1961-2015年淮河流域170站月降水资料、NCEP再分析资料和ERSST海温资料,采用滑动相关、合成分析等方法来探讨厄尔尼诺/拉尼娜与淮河流域汛期降水年际关系的稳定性。结果表明:厄尔尼诺/拉尼娜与淮河流域汛期降水的年际关系存在不稳定性,两者11年滑动相关在1979年出现一次突变,1961-1979年两者为明显的负相关,1980-1992年为正常阶段,1993-2015年为明显的正相关。文中主要讨论两个明显相关时段厄尔尼诺/拉尼娜对淮河流域降水的影响。1961-1979年时段和1993-2015年时段厄尔尼诺/拉尼娜对淮河流域夏季降水的影响是相反的,而且1993-2015年厄尔尼诺/拉尼娜对淮河流域汛期降水预测的指示意义不如1961-1979年时段。厄尔尼诺事件对淮河流域降水的影响较为明显,而拉尼娜的影响不明显,两者的影响表现出不对称的特点。1961-1979年期间厄尔尼诺发展(衰减)年夏季亚洲大气环流配置有利于南北气流在淮河流域上空汇合(辐散),使得流域降水偏多(偏少),而1993-2015年厄尔尼诺事件则相反。

黄河流域主要农作物的降水盈亏格局分析

以1961—2000年的气象资料为数据基础，采用FAO 1998年推荐使用的Penman—Monteith模型和参考作物法，对黄河流域不同类型旱农地区主要农作物的降水盈亏格局进行了分析。结果表明：黄河流域大部分地区冬小麦全生育期多年平均缺水量在250～500mm，且由南向北缺水量有依次递增的趋势，主要反映了冬小麦全生育期降水量与需水量的双重影响；夏玉米全生育期缺水量较多的地区为陕西省关中地区，约为200mm左右，由此向东缺水量值逐渐减少；春小麦全生育期多年平均缺水量基本上是从南向北逐渐升高，缺水量在200—500mm，显然是受降雨与需水两方面的双重影响；春玉米全生育期多年平均缺水量分布则是从南部向北部递增，亏缺量在0～400mm。

数字流域模型关键技术研究

数字流域模型定位于大范围、全流域级的水文过程模拟,是一个具有多层空间分辨率的、模型参数可以容易获取的、能够实现并行计算的全流域级整体模型。数字流域模型的建立需要解决5项关键技术问题,即大流域DEM数据存取技术、流域沟道参数提取技术、基于遥感图像的模型参数提取技术、分布式降雨量数据存取技术、计算机集群并行计算技术。在黄河数字流域模型的建设实践中,提出了5项关键技术问题的解决方法:用分块技术解决大流域DEM数据的存取问题,用TOPAZ模块提取流域沟道参数,用遥感图像提取模型分布式参数,用雨量站插值技术存取面雨量序列,用计算机并行计算技术打破大流域整体模型的计算瓶颈。

厄尔尼诺与黄河流域汛期降雨洪水的关系分析

分析了1951年以来历次厄尔尼诺现象出现后黄河流域各区间汛期降水的主要特征,认为厄尔尼诺现象与黄河流域降雨洪水的关系具有以下主要特点:①在厄尔尼诺次年,黄河流域各区间汛期降水量偏多的几率较非厄尔尼诺次年要大,没有出现距平≤-50%的特少年份;②黄河中游以及兰州至托克托区间厄尔尼诺次年的汛期降雨总量偏多20%以上的几率明显大于气候概率,特别是晋陕区间偏多20%以上的年份占到46.7%;③花园口洪峰流量超过10 000 m3/s的大洪水都发生在厄尔尼诺现象出现的当年或次年;④厄尔尼诺次年黄河下游汛期降雨量正常的年份很少。

1961-2019年黄河流域降雨侵蚀力时空变化特征分析

请研究基于黄河流域317个气象站1961-2019年逐日降雨资料,采用日降雨侵蚀力计算模型计算各站点降雨侵蚀力,统计分析了流域降雨侵蚀力的时空分布特征及其与地理因子和气象因子的关系,从总体趋势角度综合探讨导致土壤水蚀加剧的原因,以期为黄河流域生态保护和高质量发展提供技术支撑。结果表明:1)黄河流域1961-2019年平均降雨侵蚀力为1223.1 MJ·mm/(hm^(2)·h·a),整体呈不显著下降趋势,下降速率为每10a下降6.71 MJ·mm/(hm^(2)·h·a)。降雨侵蚀力夏高冬低,夏季降雨侵蚀力占全年的61.3%,冬季仅占0.3%。2)黄河流域多年平均降雨侵蚀力值的分布范围为33.0~3550.6 MJ·mm/(hm^(2)·h·a),空间分布呈从西北到东南递增的规律。3)降雨侵蚀力与各地理因子均呈极显著相关关系,其中与经度和坡度呈正相关,相关系数分别为0.587和0.164(n=317,P<0.01),与纬度和海拔高度呈负相关,相关系数分别为-0.498和-0.490(n=317,P<0.01);降雨侵蚀力与降雨量、降水日数、雨强和暴雨日数均呈极显著正相关关系,相关系数分别为0.839、0.208、0.819和0.753(n=317,P<0.01)。逐步回归分析显示,降雨量对降雨侵蚀力的贡献率最大,降雨量是导致降雨侵蚀力变化的最主要因素。

6月长江中下游降水和春季东亚季风区土壤湿度的关系

利用美国气候预测中心(CPC)土壤湿度资料、中国台站观测降水资料以及NCEP/NCAR再分析的风场和气温资料,在去除了降水资料中的ENSO信号的影响后,分析了6月长江中下游降水和春季东亚季风区土壤湿度的关系。结果表明,长江中下游6月降水和前期春季土壤湿度存在很显著的正相关关系。进一步分析表明,当中晚春(4—5月)长江中下游地区的土壤湿度偏高(低)时,晚春(5月)长江中下游上空低层气温偏低(高),从而导致东亚季风区的海陆温差减小(增加)。海陆温差的减弱(增强)使得6月东亚夏季风较常年偏弱(强),伴随的风场异常主要体现在长江以南地区为南风(北风)异常所控制,而长江以北则为北风(南风)异常,从而使得长江中下游存在着异常辐合(散),最终导致长江中下游降水量较常年偏多(少)。