Important factors governing the incompatible trends of annual pan evaporation: evidence from a small scale region

Many studies reported the coexisting trends of decreasing and increasing pan evaporation in some large scale regions. This study proved that the coexisting trends also occurred in small scale region as well as in large scale region. To discover the important factors governing the incompatible trends of annual pan evaporation, annual climatic data of ten meteorological stations at the Liaohe Delta over recent 45 years were analyzed by the partial correlation analysis, and the results showed the strongest statistically correlation between annual relative humidity and annual pan evaporation. Researches on two extreme cases suggested there was obvious contrary trend between annual relative humidity and annual pan evaporation for one case, in despite of slight contrary trend for another case. Generally, annual relative humidity most likely was an important factor relating to the trend of annual pan evaporation. At the same time, an expanded urbanization and irrigation were seen around these meteorological stations. Urbanization and irrigation exerted opposite effects on pan evaporation, they therefore were speculated to be the ultimately inducements causing unbalanced relative humidity, and led to incompatible pan evaporation.     

A high-quality monthly total cloud amount dataset for Australia

A high-quality monthly total cloud amount dataset for 165 stations has been developed for monitoring and assessing long-term trends in cloud cover over Australia. The dataset is based on visual 9 a.m. and 3 p.m. observations of total cloud amount, with most records starting around 1957. The quality control process involved examination of historical station metadata, together with an objective statistical test comparing candidate and reference cloud series. Individual cloud series were also compared against rainfall and diurnal temperature range series from the same site, and individual cloud series from neighboring sites. Adjustments for inhomogeneities caused by relocations and changes in observers were applied, as well as adjustments for biases caused by the shift to daylight saving time in the summer months. Analysis of these data reveals that the Australian mean annual total cloud amount is characterised by high year-to-year variability and shows a weak, statistically non-significant increase over the 1957–2007 period. A more pronounced, but also non-significant, decrease from 1977 to 2007 is evident. A strong positive correlation is found between all-Australian averages of cloud amount and rainfall, while a strong negative correlation is found between mean cloud amount and diurnal temperature range. Patterns of annual and seasonal trends in cloud amount are in general agreement with rainfall changes across Australia, however the high-quality cloud network is too coarse to fully capture topographic influences. Nevertheless, the broadscale consistency between patterns of cloud and rainfall variations indicates that the new total cloud amount dataset is able to adequately describe the broadscale patterns of change over Australia. Favourable simple comparisons between surface and satellite measures of cloudiness suggest that satellites may ultimately provide the means for monitoring long-term changes in cloud over Australia. However, due to the relative shortness and homogeneity problems of the satellite record, a robust network of surface cloud observations will be required for many years to come.     

近50年来(1960—2007年)长江流域20 cm口径蒸发皿蒸发量与太阳辐射变化的对比

利用长江流域147个气象站点1960—2007年的地面观测数据,通过计算,对比分析了长江流域20 cm口径蒸发皿蒸发量与太阳辐射的变化关系.结果表明:长江流域近50年来蒸发皿蒸发量变化和太阳辐射变化呈显著正相关关系,二者均呈现显著下降趋势,蒸发皿蒸发量随太阳辐射的变化产生相应波动变化,而且中下游地区蒸发皿蒸发量变化受太阳辐射变化的影响程度更为明显;就季节变化而言,春夏秋冬4个季节长江流域蒸发皿蒸发量变化和太阳辐射变化同样呈现明显下降趋势,春、夏、秋3个季节二者变化关系高度相关,这三季对于流域全年蒸发皿蒸发量减少的贡献也最大;长江流域太阳辐射的显著下降是导致20 cm口径蒸发皿蒸发量持续降低的主要原因之一.     

商丘近44年蒸发量变化及其影响因子分析

利用商丘市8个台站1961~2004年的20 cm口径蒸发皿资料,进行蒸发量的年际变化、年代际变化、季节变化以及月分布的分析,结果显示蒸发量存在显著的减少趋势。年际间减少趋势通过了99%的置信度水平,各季节蒸发量以春季和夏季减少最为明显。同时还分析了近44年来日照、风速和温度的变化趋势,并计算了这些气象因子与蒸发量变化的相关系数。分析表明日照时数减少和风速减小是造成商丘市蒸发量下降的主要因素,而气温上升对蒸发量的影响不十分明显。     

小型与E-601型蒸发皿蒸发量对比分析及其折算系数——以江苏省为例

本文基于江苏省16个台站小型和E-601型蒸发皿同步对比观测资料,以南京站为例,采用比值法和多元线性回归法对长时间序列小型蒸发皿蒸发量进行估算及效果检验,结果表明:通过比值法计算得到的月折算系数介于0.490～0.609之间,年折算系数介于0.476～0.621之间,二者平均折算系数相同,均为0.537,两种蒸发皿月蒸发量相关系数高达0.952 4,年蒸发量相关系数仅0.496 2,表明在利用比值法进行计算时,月折算系数较为合理,具有较好适用性;基于各气象因子和E-601型蒸发量建立的各月小型蒸发皿蒸发量多元线性回归方程,决定系数介于0.809～0.940,效果较理想;比值法和多元线性回归法模拟检验中,比值法年平均误差为7.9%,多元线性回归法年平均误差仅2.5%,比值法预测结果决定系数为0.861 9,回归模型决定系数高达0.953 4,可见回归模型效果更为理想。总结研究结果后,本文详细给出江苏省各台站小型及E-601型蒸发皿折算系数,为有效完整利用江苏省各台站长时间序列小型蒸发皿资料提供合理依据。     

广东省年蒸发量的时空演变特征

利用广东省86个气象站点1961—2003年的地面气象观测数据,采用经验正交函数分解（EOF）和相关分析法,分析了广东省年蒸发皿蒸发量和实际蒸发量的时空变化。结果表明,粤东沿海、珠三角和粤西南等沿海地区是广东省年蒸发皿蒸发量的主要气候变异中心,广东省沿海年蒸发皿蒸发量具有以年代际变化为主的特征,并且在43 a内总体上呈下降趋势,广东省沿海地区与粤东、粤中地区年蒸发皿蒸发量气候变化趋势的差异,可能是由于饱和差、近地面风速在两个区域的气候变化变幅不同所致。在影响蒸发皿蒸发量的因子中,太阳辐射与蒸发皿蒸发量的相关性最好,呈显著的正相关。对实际蒸发量而言,在全省范围内均表现为以年际变化为主的特征,太阳辐射对广东省年实际蒸发量的影响最为显著,广东省年实际蒸发量一般都占蒸发皿蒸发量的50%左右,并且比值总体上呈现微弱的由沿海地区向粤东、粤中地区递增的趋势。研究结果可为今后探讨广东省水资源异常和旱涝气候灾害的成因提供依据。     

Variability and trends of sub-continental scale surface climate in the twentieth century. Part I: observations

An analysis is presented of observed temperature and precipitation variability and trends throughout the twentieth century over 22 land regions of sub-continental scale. Summer, winter and annual data are examined using a range of variability measures. Statistically significant warming trends are found over the majority of regions. The trends have a magnitude of up to 2 K per century and are maximum over cold climate regions. Only a few precipitation trends are statistically significant. Regional temperature and precipitation show pronounced variability at scales from interannual to multidecadal, with maximum over cold climate regions. The interannual variability shows significant variations and trends throughout the century, the latter being mostly negative for precipitation and both positive and negative for temperature. Temperature and precipitation anomalies show a chaotic-type behavior in which the regional conditions oscillate around the long term mean trend and occasionally fall into long-lasting (up to 10 years or more) anomaly regimes. A generally modest temporal correlation is found between anomalies of different regions and between temperature and precipitation anomalies for the same region. This correlation is mostly positive for temperature in cases of adjacent regions or regions in the same latitude belts. Several cases of negative inter-regional precipitation anomaly correlation are found. The ENSO significantly affects the anomaly variability patterns over a number of regions, primarily in tropical areas, while the NAO significantly affects the variability over northern mid- and high-latitude regions of Europe and Asia.     

1960—2009年北京地区城市化背景下蒸发皿蒸发量的时空变化

利用1960—2009年北京地区20个气象台站的观测资料,分析了北京城区和郊区蒸发皿蒸发量的季节和年际变化趋势和特点,并探讨了城市化对北京地区局地气候的影响。结果表明:近50 a北京地区蒸发量有明显减小趋势,城区和郊区变化趋势分别为-88.1 mm/10a和-76.0 mm/10a。受城市化影响,北京城区蒸发量的变化主要与降水、日照时数、最低气温、气温日较差和平均风速的变化有关;郊区蒸发量的变化主要受相对湿度、日照时数、平均风速和空气饱和差的变化影响。总体而言,相对湿度、日照时数、最低气温、气温日较差和平均风速的变化对北京地区蒸发量的变化有显著影响。     

Changes of pan evaporation and reference evapotranspiration in the Yangtze River basin

Summary For the upper and mid-lower Yangtze River basin trends of pan evaporation and reference evapotranspiration are analysed from 1961 to 2000 using daily data of 115 stations. Both pan evaporation and reference evapotranspiration decreased during the summer months contributing most to the total annual reduction. This trend is more significant in the mid-lower than in the upper Yangtze reaches. The decreasing trends can be associated with trends in net radiation and wind speed. Results are compared with the 20th century evaporation simulated by the general circulation model (GCM, ECHAM5/MPI-OM). Also the GCM’s actual evaporation decreases contrasting an overall increase in air temperature.     

石羊河流域1960～2009年参考蒸散量与蒸发皿蒸发量变化特征

以石羊河流域5个气象站点1960～2009年逐日气象资料为基础,从估算模型和统计角度计算分析了该流域参考蒸散量及蒸发皿蒸发量的变化趋势和变化原因。结果表明：过去50 a石羊河流域蒸散发呈增加趋势,个别站点达极显著水平（p＜0．01）,1960～2009年和1970～2009年不同时段的选择对分析结果有一定的影响。估算模型理论分析认为桑斯威特法计算的参考蒸散量变率主要由气温决定,蒸发皿蒸发量和彭曼蒙蒂斯公式计算的参考蒸散量变化则是辐射、气温、风速及空气饱和差共同作用的结果,而相关分析和突变检验的分析结果验证了上述结论,并得出过去50 a石羊河流域蒸发皿蒸发量和彭曼蒙蒂斯公式计算的参考蒸散量变化的主要决定因素是空气饱和差。     

Comparison of Ten Potential Evapotranspiration Models and Their Attribution Analyses for Ten Chinese Drainage Basins

Potential evapotranspiration(E_(PET)) is usually calculated by empirical methods from surface meteorological variables,such as temperature, radiation and wind speed. The in-situ measured pan evaporation ET_(pan) can also be used as a proxy for E_(PET). In this study, E_(PET) values computed from ten models are compared with observed ET_(pan) data in ten Chinese river basins for the period 1961-2013. The daily observed meteorological variables at 2267 stations are used as the input to those models, and a ranking scheme is applied to rank the statistical quantities(ratio of standard deviations, correlation coefficient, and ratio of trends) between ET_(pan) and modeled E_(PET) in different river basins. There are large deviations between the modeled E_(PET) and the ET_(pan) in both the magnitude and the annual trend at most stations. In eight of the basins(except for Southeast and Southwest China), ET_(pan) shows decreasing trends with magnitudes ranging between-0.01 mm d~(-1) yr~(-1) and-0.03 mm d~(-1) yr~(-1), while the decreasing trends in modeled E_(PET) are less than-0.01 mm d~(-1) yr~(-1). Inter comparisons among different models in different river basins suggest that PET_(Ham1) is the best model in the Pearl River basin, PET_(Ham2) outperforms other models in the Huaihe River, Yangtze River and Yellow River basins, and PET_(FAO) is the best model for the remaining basins. Sensitivity analyses reveal that wind speed and sunshine duration are two important factors for decreasing E_(PET) in most basins except in Southeast and Southwest China. The increasing E_(PET) trend in Southeast China is mainly attributed to the reduced relative humidity.     

Trends and scales of observed soil moisture variations in China

A new soil moisture dataset from direct gravimetric measurements within the top 50-cm soil layers at 178 soil moisture stations in China covering the period 1981-1998 are used to study the long-term and seasonal trends of soil moisture variations, as well as estimate the temporal and spatial scales of soil moisture for different soil layers. Additional datasets of precipitation and temperature difference between land surface and air (TDSA) are analyzed to gain further insight into the changes of soil moisture. There are increasing trends for the top 10 cm, but decreasing trends for the top 50 cm of soil layers in most regions. Trends in precipitation appear to dominantly influence trends in soil moisture in both cases. Seasonal variation of soil moisture is mainly controlled by precipitation and evaporation, and in some regions can be affected by snow cover in winter. Timescales of soil moisture variation are roughly 1-3 months and increase with soil depth. Further influences of TDSA and precipitation on soil moisture in surface layers, rather than in deeper layers, cause this phenomenon. Seasonal variations of temporal scales for soil moisture are region-dependent and consistent in both layer depths. Spatial scales of soil moisture range from 200-600 km, with topography also having an affect on these. Spatial scales of soil moisture in plains are larger than in mountainous areas. In the former, the spatial scale of soil moisture follows the spatial patterns of precipitation and evaporation, whereas in the latter, the spatial scale is controlled by topography.     

Long-term Changes in the Main Components of Lake Khanka Water Regime

Changes in annual total precipitation and annual pan evaporation for the Lake Khanka water area during the period of 1949–2015 are analyzed based on observational data of weather stations within the lake basin. The reliability of the calculated values of characteristics affecting evaporation changes was confirmed by their comparison with observations at the 20-m² evaporation pan installed at Astrakhanka lake station. It is shown that against a background of significant interannual fluctuations of annual precipitation during the whole period under study, its trends are almost absent. However, a rather stable increase in annual precipitation value caused by the summer precipitation rise has been noted since the early 2000s. The value of annual pan evaporation decreased from 1949 to 2015, and the rate of its decrease till 1980 was higher than in the next period. Moreover, some evaporation increase has been observed in the recent decade. The main contribution to the evaporation change is made by wind speed changes which cause about 50% of evaporation variance. Air humidity deficit is the second affecting factor that determines a little over 20% of annual evaporation variance. It is demonstrated that the increase in annual precipitation is possible by the middle of the 21st century, while the change in annual evaporation from the Lake Khanka water area would be minimal. Under such changes in the main components of the lake water regime, no reduction of its level due to natural climate processes should be expected.     

我国东部梅雨期降水的年际和年代际变化特征及其与大气环流和海温的关系

基于我国160站59年(1951～2009年)的月降水观测资料、美国气象环境预报中心和国家大气研究中心(NCEP/NCAR)提供的再分析资料和Hadley中心的海表温度(Sea Surface Temperature,简称SST)资料,对我国东部(100°E以东,15°N～40°N)梅雨期(6月和7月)降水的时空变化特...     

中国均一化日平均温、最高温和最低温序列1960-2008

Inhomogeneities in the daily mean/maximum/ minimum temperature （Tm/Tmax/Tmin） series from 1960- 2008 at 549 National Standard Stations （NSSs） in China were analyzed by using the Multiple Analysis of Series for Homogenization （MASH） software package. Typical biases in the dataset were illustrated via the cases of Beijing （B J）, Wutaishan （WT）, Urumqi （UR） and Henan （HN） stations. The homogenized dataset shows a mean warming trend of 0.261/0.193/0.344℃/decade for the annual series of Tm/Tmax/Tmin, slightly smaller than that of the original dataset by 0.006/0.009/0.007℃/decade. However, considerable differences between the adjusted and original datasets were found at the local scale. The adjusted Tmin series shows a significant warming trend almost everywhere for all seasons, while there are a number of stations with an insignificant trend in the original dataset. The adjusted Tm data exhibit significant warming trends annually as well as for the autumn and winter seasons in northern China, and cooling trends only for the summer in the middle reaches of the Yangtze River and parts of central China and for the spring in southwestern China, while the original data show cooling trends at several stations for the annual and seasonal scales in the Qinghai, Shanxi, Hebei, and Xinjiang provinces. The adjusted Tmax data exhibit cooling trends for summers at a number of stations in the mid-lower reaches of the Yangtze and Yellow Rivers and for springs and winters at a few stations in southwestern China, while the original data show cooling trends at three/four stations for the annual/autumn periods in the Qinghai and Yunnan provinces. In general, the number of stations with a cooling trend was much smaller in the adjusted Tm and Tmax dataset than in the original dataset. The cooling trend for summers is mainly due to cooling in August. The results of homogenization using MASH appear to be robust; in particular, different groups of stations with consideration of elevation led to minor effects i     

1961-2010年青海高原蒸发皿蒸发量变化及其对水资源的影响

利用1961-2010年青海省气象观测资料,分析了青海高原近50年蒸发皿蒸发量的时空分布特征和变化趋势,并采用偏相关及主成分分析法,探讨了青海高原蒸发皿蒸发量变化的气候成因及其对水资源的影响。结果表明：近50 a来青海高原蒸发皿蒸发量呈显著下降趋势,它是热力、水分、动力因子综合作用的结果,在三类因子中,动力及水分因子对蒸发皿蒸发量的影响较大,而热力因子相对较小;区域分析表明,影响东部农业区和柴达木盆地蒸发量的主导因子是平均风速和相对湿度,三江源区为相对湿度,而唐古拉山区为气温日较差。通过分析黄河上游可能蒸散量与地表水资源的关系发现,蒸散量对地表水资源的负效应十分显著,其中夏季蒸散量对于平均流量的影响最为显著,而秋季平均流量对蒸散量的响应最为敏感。     

我国季平均气温和降水局地同时相关的时空特征

将1955—1998年我国160站冬、夏季平均气温和总降水量序列分解为年代际和年际变化两个部分，用方差分析、相关分析和奇异值分解方法，分析了两种要素序列的方差构成及要素间局地相关关系的性质、季节变化和地理分布。结果表明:我国冬夏季气温、降水异常序列中，总方差年际变化大于年代际变化，但按自由度均分的方差，年代际变化较年际变化大，尤以气温为甚；单站气温、降水同时相关图上，夏季表现为显著的负相关，显著区主要分布在35°N以南、105°E以东的地区；夏季局地温度、降水也呈显著负相关关系，进一步分析表明，干热、湿凉型异常夏季多发生在江淮和华南两区，但同一年中两区夏季异常型常相反，它由年代际和年际变化中的负相关共同构成。     

长江流域1961-2000年蒸发量变化趋势研究

利用长江流域115个气象站点1961-2000年的观测数据,计算了各站点的参照蒸发量和实际蒸发量,并进行了20 cm蒸发皿蒸发量、参照蒸发量和实际蒸发量时空变化趋势分析。结果表明,近40 a来,长江流域蒸发皿蒸发量、参照蒸发量和实际蒸发量的年平均变化均呈现显著下降趋势。就季节平均变化而言,春季和秋季,三者的变化趋势都不明显,而夏季三者均具有显著的下降趋势,冬季蒸发皿蒸发量和参照蒸发量均显著下降,实际蒸发量却明显上升。蒸发量的变化趋势具有空间分布差异,长江流域中下游地区蒸发量的变化趋势明显比上游地区显著,尤其表现在夏季。尽管近20余年长江流域气温不断升高,但太阳净辐射和风速的显著下降,可能是导致蒸发量持续降低的主要原因。     

近40年京津冀蒸发皿蒸发量变化特征及影响因子

为了研究京津冀地区蒸发皿蒸发量的变化特征及成因,在京津冀地区200多个气象站中选择资料序列完整且具有较长时间序列、测站环境评分都在70分以上(按照中国气象局对测站探测环境评分标准评分)、均匀分布的87个气象站,利用1970—2013年京津冀地区87个气象站蒸发皿蒸发量以及其他气象要素的观测资料,采用线性倾向估计法和完全相关系数法,分析近44年来京津冀蒸发量变化特征及影响因子。结果表明,近44年来,京津冀地区年、季蒸发量呈明显下降趋势。全年蒸发量减少速率由大到小分别为:山前平原区太行山区冀东平原区燕山丘陵区冀北高原区(蒸发速率由北向南逐渐增大);四季中下降速率为:春季秋季冬季夏季。分析蒸发量与影响因子的完全相关系数发现,气温日较差、日照时数和平均风速是影响京津冀地区蒸发皿蒸发量变化的主要因子,在平原地区,平均风速是主导因子;在山区和高原地区,日照时数是主导因子。     

LICOM Model Datasets for the CMIP6 Ocean Model Intercomparison Project

The datasets of two Ocean Model Intercomparison Project(OMIP)simulation experiments from the LASG/IAP Climate Ocean Model,version 3(LICOM3),forced by two different sets of atmospheric surface data,are described in this paper.The experiment forced by CORE-II(Co-ordinated Ocean–Ice Reference Experiments,Phase II)data(1948–2009)is called OMIP1,and that forced by JRA55-do(surface dataset for driving ocean–sea-ice models based on Japanese 55-year atmospheric reanalysis)data(1958–2018)is called OMIP2.First,the improvement of LICOM from CMIP5 to CMIP6 and the configurations of the two experiments are described.Second,the basic performances of the two experiments are validated using the climatological-mean and interannual time scales from observation.We find that the mean states,interannual variabilities,and long-term linear trends can be reproduced well by the two experiments.The differences between the two datasets are also discussed.Finally,the usage of these data is described.These datasets are helpful toward understanding the origin system bias of the fully coupled model.