1961-2004年青藏高原夏季降水的时空分布

The summer day-by-day precipitation data of 97 meteorological stations on the Qinghai-Tibet Plateau from 1961 to 2004 were selected to analyze the temporal-spatial distribution through accumulated variance,correlation analysis,regression analysis,empirical orthogonal function,power spectrum function and spatial analysis tools of GIS.The result showed that summer precipitation occupied a relatively high proportion in the area with less annual precipitation on the Plateau and the correlation between summer precipitation and annual precipitation was strong.The altitude of these stations and summer precipitation tendency presented stronger positive correlation below 2000 m,with correlation value up to 0.604（α=0.01）.The subtracting tendency values between 1961-1983 and 1984-2004 at five altitude ranges（2000-2500 m,2500-3000 m,3500-4000 m,4000-4500 m and above 4500 m）were above zero and accounted for 71.4%of the total.Using empirical orthogonal function, summer precipitation could be roughly divided into three precipitation pattern fields：the Southeast Plateau Pattern Field,the Northeast Plateau Pattern field and the Three Rivers＇ Headstream Regions Pattern Field.The former two ones had a reverse value from the north to the south and opposite line was along 35°N.The potential cycles of the three pattern fields were 5.33a,21.33a and 2.17a respectively,tested by the confidence probability of 90%.The station altitudes and summer precipitation potential cycles presented strong negative correlation in the stations above 4500 m,with correlation value of-0.626（α=0.01）.In Three Rivers Headstream Regions summer precipitation cycle decreased as the altitude rose in the stations above 3500 m and increased as the altitude rose in those below 3500 m.The empirical orthogonal function analysis in June precipitation,July precipitation and August precipitation showed that the June precipitation pattern field was similar to the July＇s,in which southern Plateau was positive and northern Plateau negative.But positive     

近44年来青藏高原夏季降水的时空分布特征

利用1961-2004 年青藏高原97 个站点的夏季逐日降水数据,通过累积距平、相关分析、回归分析、经验正交函数分解、功率谱方法等,结合GIS 的空间分析功能,分析了夏季 降水的时空分布特征。结果表明：在青藏高原年降水量比较少的地区,夏季降水占全年降水的比例较高,夏季降水与全年降水的相关性也较强;夏季降水相对变率最大的地区位于青藏 高原西北的最干旱地区,最小的地区是三江源区;夏季降水趋势增加和减少的站点分别为54 个和43 个,通过较显著检验的站点占总数的18.6%;在2000m 以下的站点中,海拔和夏季降水气候倾向率存在较强的正相关,相关度达0. 604 (显著性0.01);1961-1983 年和1984-2004 年两个时间段相比,除了3000~3500m 海拔范围外,其余海拔范围夏季降水气候倾向率都表现为增加;夏季降水可大致分为三种类型场：高原东南部类型场、高原东北部类型场和三江 源类型场,高原东南部类型场和高原东北部类型场表现出南北变化相反的降水特点,分界线大致沿着35^oN 线;在90%的置信概率下,三种类型场分别表现出5.33 年、21.33 年和2.17 年的潜在周期;4500 m 以上海拔范围的站点夏季降水周期通过很显著检验(α = 0.01),站点海拔和降水周期存在-0.626 的高相关度;在三江源地区,3500 m 以上的站点夏季降水周期随海拔升高而减小,3500 m 以下的夏季降水周期随海拔高度升高而增加。     

青藏高原及其邻近地区的水汽分布特征

本文利用青藏高原及其邻近地区20多个测站1882年3月-1983年7月的温湿度探空资料,计算了对流层内气柱的含水量,讨论了它们的时空变化特征。在此基础上用拟合得到的气柱中的含水量与地面水汽压、气压的相关方程,进一步计算并阐述了青藏高原及其邻近地区各个季节的水汽量分布。     

基于TRMM数据的青藏高原降水的空间和季节分布特征

庞大的青藏高原不仅影响其周围的气候,也影响整个亚洲甚或全球的气候,而且本身还形成了独特的高原气候。但高原上气象观测站点极为稀少,降水资料奇缺,难以完整、深刻地认识高原降水的时空分布格局。选用热带降雨测量计划卫星(Tropical Rainfall Measuring Mission,TRMM)3B43月尺度降水率数据,并根据114个气象站点数据与TRMM数据的差额和克里格球形插值模型对原数据进行了修正,克服了原数据低值高估、高值低估的问题,并以此分析了青藏高原1998~2011年的多年平均降水的空间格局与季节分布特征。研究结果证实了青藏高原降水的空间格局呈现自东南向西北递减、自南向北逐渐减少的基本分布规律,包括喜马拉雅山北坡雨影区、高原西北部"寒旱核心"的存在;还发现了一些新的规律,包括阿里喀喇昆仑山少雨区、高原腹地相对湿润区、横断山脉中心相对干旱区等。高原降水的季节分配不均匀,其中,西、北部春(3~5月)、秋(9~11月)和冬(12~2月)的降水占全年降水比例均为20%~30%,夏季(6~8月)降水稍多,比例为30%~40%;东南部降水主要集中在夏季,比例高达40%~60%,春、秋降水比例为20%~30%,冬季降水比例低于10%。     

青藏高原降水季节分配的空间变化特征

青藏高原是全球气候变化影响的敏感区域。在全球气候变暖的背景下,其水文气候过程发生了显著的变化,直接影响到区域水资源演化。然而,目前对该区域水文气候过程的时空演变规律仍认识不足。本文以青藏高原气象站点降水观测数据为基准,结合水汽通量资料,对13种不同源降水数据集质量进行对比分析;并选用质量较好的IGSNRR数据集识别了青藏高原降水季节分配特征的空间分布格局。结果表明,青藏高原东南、西南以及西北边缘地区降水集中度和集中期较小,夏季降水占全年降水比例不足50%;随着逐渐向高原腹地推进,降水集中度和集中期逐渐增大,雨季逐渐缩短且推迟,雨季降水占全年降水比例逐渐增大。降水季节分配的空间分布格局与水汽运移方向保持一致,即主要是由西风和印度洋季风的影响所致。基于此,识别出西风的影响区域主要位于高原35°N以北,印度洋季风的影响区域主要位于高原约30°N以南,而高原中部(30°N~35°N)降水受到西风和印度洋季风的共同影响。该结果有助于进一步理解和认识青藏高原水文气候过程空间差异性。     

青藏高原夏季上空水汽含量演变特征及其与降水的关系

利用青藏高原(以下简称高原) 近30 年(1979-2008 年) 14 个探空站的温度和湿度观测资料以及83 个地面台站的月平均降水资料,分析了高原夏季上空水汽含量与地面降水的联系以及高原地区的降水转化率问题。结果表明：1) 高原夏季水汽含量在空间分布上表现出随海拔高度增高而减少的特征,其中东北部为最大值,东南部为次大值,而西北部为最小值。夏季降水整体上由东南向西北递减;2) EOF分解表明,高原夏季水汽含量存在两种主要的空间分布型：即全区一致变化型和南北反向变化型,其中以唐古拉山脉北侧为界呈现出的水汽含量南北反向型与降水的第一特征向量场表现出的南北反向型在空间分布上十分相似;3) 在年际变化上,高原夏季水汽含量的南北反向型与降水的南北反向型之间存在较一致的对应关系：即水汽含量出现南多北少时,高原南部降水普遍偏多而北部降水普遍偏少,反之亦然;4) 高原夏季平均降水转化率在3%~38%之间,其空间差异非常明显,高原南部降水转化率明显大于北部地区。     

雅鲁藏布江流域多源降水产品评估及其在水文模拟中的应用

论文对比分析了1980—2016年基于站点插值降水数据CMA(China Meteorological Administration)和APHRODITE(Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation)、卫星遥感降水数据PERSIANN-CDR(Precipitation Estimation from Remotely Sensed Information using Artificial Neural Network-Climate Data Record)和GPM(Global Precipitation Measurement)、大气再分析数据GLDAS(Global Land Data Assimilation System)以及区域气候模式输出数据HAR(High Asia Refined analysis)在雅鲁藏布江7个子流域的降水时空描述,利用国家气象站点数据对各套降水数据进行单点验证,并以这6套降水数据驱动VIC(Variable Infiltration Capacity)大尺度陆面水文模型反向评估了各套降水产品在雅鲁藏布江各子流域径流模拟中的应用潜力。结果表明：① PERSIANN-CDR和GLDAS年均降水量最高(770~790 mm),其次是HAR和GPM(650~660 mm),CMA和APHRODITE年均降水量最低(460~500 mm)。除GPM外,其他降水产品在各子流域都能表现季风流域的降水特征,约70%~90%的年降水量集中在6—9月份。② 除PERSIANN-CDR和GLDAS外,其他降水产品皆捕捉到流域降水自东南向西北递减的空间分布特征。其中,HAR数据空间分辨率最高,表现出更详细的流域内部降水空间分布特征。③ 与对应网格内的国家气象站降水数据对比显示,APHRODITE、GPM和HAR降水整体低估(低估10%~30%),且严重低估的站点主要集中在下游(低估40%~120%)。PERSIANN-CDR和GLDAS整体表现为高估上游流域站点降水(高估28%~60%),但低估下游流域站点降水(低估11%~21%)。④ 在流域径流模拟上,当前的6套降水产品在精度或时段上仍无法满足水文模型模拟的需求。⑤ 通过水文模型反向评估,6套降水产品中区域气候模式输出的HAR在流域平均降水量和季节分配上更合理。     

青藏高原中东部水热条件与NDVI的空间分布格局

青藏高原受大气环流和地势格局的共同作用,水热条件及植被空间分布呈现独特的三维地带性特征。但是青藏高原范围广、地势起伏大,水热条件及植被空间分布具有明显区域差异。本文利用青藏高原中东部100个气象站1982²000年的降水、气温资料以及同期NO-AA AVHRR植被指数产品（NDVI）,分析水热条件及植被的空间分布特征。首先,设置经向、纬向海拔渐变样带,考察海拔对水热条件及NDVI空间分布的影响;然后,按500米海拔间隔进行站点分组,分析约束了海拔高差后的经纬位置对水热条件及NDVI空间分布的影响。研究表明:在青藏高原中东部由于海拔高差大,热量条件分布首先受海拔递减规律控制,其次才表现出因太阳辐射差异的纬度地带性;而降水分布则主要受水汽通道位置和方向的影响,北上水汽和东部偏南走向山脉是研究区降水经向特征的主要成因;指示植被状况的年均NDVI,则受水热组合的控制,其分布格局是二者的叠加与综合。     

近34 a青藏高原年降水变化及其分区

 对高原地区34 a（1971—2004年）82站共13 883 d的逐日降水量资料进行了统计,用REOF方法进行了分区,并讨论了趋势变化。青藏高原地区属季风降水区,在东亚季风、印度季风、高原季风和西风带系统的影响下,降水的局部特征显著。近34 a来高原上的降水量整体呈增加趋势,从20世纪70年代到90年代初期降水变化不大,90年代中后期开始明显增加,尤其是近3 a增加明显。青藏高原干旱地区降水完全取决于夏季降水量,并且降水的相对变率大。从青藏高原地区年降水的分区情况来看,西藏及四川的西南部降水增加最明显,每10 a增加幅度为54.5 mm,其次是青海的柴达木盆地和青海湖地区及甘肃的河西走廊地区。而青海的东部及三江源地区,祁连山区,四川的西北部地区呈减少趋势。高原上高海拔地区的降水在减少,而低海拔地区在增加。     

青藏高原近40年来的降水变化特征

利用我国青藏高原地区的1961-2000年56个气象站的逐月降水资料,通过计算降水量的距平百分率,分析了青藏高原自1961至2000年以来降水量变化的趋势和1961-2000年以来各季降水量变化趋势,发现:青藏高原近40年来降水量呈增加趋势,降水量的线性增长率约为1.12mm/a。再将高原划分为四个季节,分析了各季40年来的降水量的变化情况得出:春季降水量年际变化较大,秋季降水量变化不明显。夏季降水量值较大而降水变化幅度较小,冬季降水量变化则与夏季相反。通过将青藏高原分为南北两个地区,分析了两个区的年降水量和四个季节的降水量的变化得出:高原南区1961-2000年降水量呈增加的趋势,降水量的线增长率为1.97 mm/a,春季和冬季降水量年际变化较大,夏季降水量变化不明显,秋季降水量略有增加;北区年降水量和夏季的降水量变化较小,秋季降水量的年际变化较大,冬季降水量变化最大。对青藏高原的南北两区用Mann-Kendall方法进行突变分析,显示高原南区分别在1978年和1994年发生突变,北区没有发现突变。     

冬夏季温度和降水变化对青海湖全新世环境变化的影响初探

青海湖是国内最大的内陆湖泊,位于青藏高原东北缘,因其处在东亚夏季风、印度季风和西风带的交替控制区域,对气候变化十分敏感,成为古环境变化研究的热点地区。有关青海湖的形成演化、环境变化和水文变化的研究也存在多种观点。本研究再分析了青海湖已报道的古环境指标和气候模式模拟的夏季、冬季温度和降水变化,力图更加全面地理解青海湖全新世以来的古环境变化。研究发现早全新世11~8 ka夏季降水量和表面蒸发量较大,冬季降水稀少,湖泊水位只有十余米深,使得青海湖周边风沙活动频繁。并且,早全新世的气候不稳定,经历了频繁和较大幅度的波动。全新世气候适宜期出现在8~6 ka,古环境指标指示这一时期为温暖湿润的气候环境,湖盆内植被以森林草原为主,湖泊水位不断上升。青海湖地区的夏季降水自6 ka开始减少,然而冬季降水增加,同时夏季温度和蒸发量减少,使得湖区植被组成由森林草原向高山草甸转变,湖区大范围形成古土壤。湖区古环境条件在晚全新世距今1.5 ka开始恶化,冬季和夏季降水同时减少,湖泊水位下降,风沙活动再次加强。     

近48年青藏高原强降水量的时空分布特征

基于青海和西藏地区48个气象台站近48 a(1961~2008年)的逐日降水资料,分析青藏高原冬、夏半年强降水量的时空演变特征。结果表明:青藏高原强降水量与总降水量的空间分布相似,夏半年为由东南向西北递减,冬半年则由唐古拉山脉东段的高原腹地向四周递减;夏(冬)半年强降水量存在准3、准6 a(7~8 a)的年际振荡以及准9~10 a(15 a)的年代际振荡;夏半年高原北(南)部强降水量以增加(减少)趋势为主,强降水量呈现出微弱的减少趋势,而冬半年高原大多数地区均呈现出明显的增加趋势,在1976年发生突变现象。     

青藏高原植被垂直带与气候因子的空间关系

集成了青藏高原气候区149个山地植被垂直带数据,利用国家基本气象台站自建站以来到2001年的地面观测日气象数据,计算了地面的温暖(WI)、寒冷(CI)、湿润(MI)、吉良龙夫(Kira)干湿指数、干燥度(Idm)等水热指数,运用GIS的空间分析模块,模拟了青藏高原水热条件的空间分布形势,探讨山地植被垂直带谱分布规律与制约因子的定量指标.结果表明:在高原的东北部、西北边缘,以荒漠、荒漠草原、山地森林、山地草原、灌丛、草甸为组合的半干旱、干旱结构向高原腹地以高寒草原、高山草甸、荒漠带组合的高寒干旱带谱结构的变化;东南、南部边缘,以温暖湿润为特征的以森林带为优势带谱组合结构逐渐向寒冷的高原中心变化;高原的地势效应,致使的水热形势旱现从中央向边缘变化的趋势是致使青藏高原植被垂直带谱分布的重要原因.     

Characteristics of mineral element content of alpine vegetation in permafrost region on Qinghai-Tibetan Plateau

The content characteristics of 16 elements (Al, Ca, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, and Zn) in 23 plant species collected from the Qinghai-Tibetan Plateau permafrost region were investigated using ICP-OES. Results show that the average contents of Ca, K, Mg, Fe and P were higher than 1,000 mg/kg, those of Al, Na, Zn and Cr ranged between 10–1,000 mg/kg and those of Cu, Li, Pb and Mo were less than 10 mg/kg. The levels of Al, Ca, K, Mg and Na were within the scope of the reported terrestrial plant element content, those of Sr, Fe and Cr were higher than the average of the terrestrial plants and the maximum content of Mn was higher than the upper limit of the reported Mn content. The main character of the element content was of the Ca>K type, however, in terms of Cyperaceae species the element content character was K>Ca type. The contents of Ca, Li, Mg and Sr in Gramineae and Cyperaceae species were higher than those in other species and the contents of Ca, K, Mg, Fe, P, Al and Na in all collected plants were higher than those of other elements. Zn had weak variability with the lowest coefficient (i.e., 7.81%), while other elements had strong variability. The ratio of maximum content to minimum content indicated Ca and K had less change than other elements in the Qinghai-Tibetan Plateau permafrost region. Element content of alpine vegetation in the Qinghai-Tibetan Plateau permafrost region mainly shows a positive correlation, among which the correlation coefficient between Al and Pb, Al and Fe, Mo and Cr, Pb and Fe, Sr and Li were higher than 0.9, and negative correlation had no statistical significance. The correlation between Al and Fe, Mg, Mn in the Qinghai-Tibetan Plateau permafrost region were consistent with that reported in Kunlun Mountains.     

Spatial Distribution Modelling of Kobresia pygmaea (Cyperaceae) on the Qinghai-Tibetan Plateau

Kobresia pygmaea Willd. dominates the alpine meadow ecosystem on the Qinghai-Tibet Plateau. Knowledge of this species’ distribution and ecological environment could provide valuable insights into the alpine ecosystem and key species living there, support species and ecosystem conservation in alpine regions, and build on species origin and evolutionary research. To avoid modelling uncertainty encountered in a single approach, four species distribution model algorithms (Surface Range Envelope (SRE), Generalized Linear Model (GLM), Generalized Boosted Regression (GBM) and Maximum Entropy (MAXENT)), were used to simulate the distribution of K. pygmaea based on occurrence samples that were verified using DNA sequencing techniques. Species distribution modelling revealed a vast distribution region of K. pygmaea in the northern Tibetan Highlands and alpine meadows in the southern and eastern declivity of the plateau. A high evaluation performance was found for the GLM, GBM and MAXENT models. Different potential range size patterns for the four models were found between 374340-482605 km² (average = 421591 km²). Precipitation during growing seasons was found to be the dominant factor accounting for the distribution, consistent with patterns of heat and water patterns conditions of alpine ecosystems on the plateau. Species distribution models provide a simple and reliable approach to simulating the spatial patterns of species inhabiting the Qinghai-Tibet Plateau.     

The evapotranspiration and environmental controls of typical underlying surfaces on the Qinghai-Tibetan Plateau

To reveal the characteristics of evapotranspiration and environmental control factors of typical underlying surfaces(alpine wetland and alpine meadow)on the Qinghai-Tibetan Plateau,a comprehensive study was performed via in situ observations and remote sensing data in the growing season and non-growing season.Evapotranspiration was positively correlated with precipitation,the decoupling coefficient,and the enhanced vegetation index,but was energy-limited and mainly controlled by the vapor pressure deficit and solar radiation at an annual scale and growing season scale,respectively.Compared with the non-growing season,monthly evapotranspiration,equilibrium evaporation,and decoupling coefficient were greater in the growing season due to lower vegetation resistance and considerable precipitation.However,these factors were restricted in the alpine meadow.The decoupling factor was more sensitive to changes of conductance in the alpine wetland.This study is of great significance for understanding hydro-meteorological processes on the Qinghai-Tibetan Plateau.     

Winter estimation of surface roughness length over eastern Qinghai-Tibetan Plateau

Based on the Monin-Obukhov similarity theory, a scheme was developed to calculate surface roughness length. Surface roughness length over the eastern Qinghai-Tibetan Plateau during the winter season was then estimated using the scheme and eddy covariance measurement data. Comparisons of estimated and measured wind speeds show that the scheme is feasible to calculate surface roughness length. The estimated roughness lengths at the measurement site during unfrozen,frozen and melted periods are 3.23×10-3, 2.27×10-3 and 1.92×10-3 m, respectively. Surface roughness length demonstrates a deceasing trend with time during the winter season. Thereby, setting the roughness length to be a constant value in numerical models could lead to certain degree of simulation errors. The variation of surface roughness length may be caused by the change in land surface characteristic.