基于遥感的黄河三角洲蒸散的动态分析

Evapotranspiration (ET) is an important parameter for water resource management. Compared to the traditional ET computation and measurement methods, the ET computation method based on remote sensing has the advantages of quickness, precision, raster mapping and regional scale. SEBAL, an ET computation model using remote sensing method is based on the surface energy balance equation which is a function of net radiance flux, soil heat flux, sensible heat flux and latent heat flux. The former three fluxes can be computed through the parameters retrieved from remote sensing image, then the latent heat flux can be obtained to provide energy for ET. Finally we can obtain the daily ET. In this study SEBAL was applied to compute ET in the Yellow River Delta of China where water resource faces a rigorous situation. Three Landsat TM images and meteorology data of 1999 were used for ET computation, and spatial and temporal change patterns of ET in the Yellow River Delta were analysed.     

华南秋季干旱的年代际转折及其与热带印度洋热含量的关系

采用1961—2014年逐月全球标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index,SPEI)数据集、ORA-S4海温资料及NCEP/NCAR再分析资料,对华南地区秋季干旱的年代际转折及其与热带印度洋热含量的关系进行了研究。结果表明:华南秋季SPEI主要表现为全区一致变化型,且具有明显的年代际变化特征,在1988年发生了年代际转折,转折后(前)为偏旱(涝)期。进一步分析表明,华南秋季SPEI与同期热带西印度洋海洋热含量变化呈显著的正相关关系,即当秋季热带西印度洋热含量偏低时,华南地区SPEI偏小,易发生干旱。热带西印度洋热含量异常影响华南秋季干旱的可能机制为:秋季热带印度洋热含量变化表现为""型的东西向偶极子分布,即当热带西印度洋热含量偏低时,热带东印度洋热含量将会偏高;而热带东印度洋热含量偏高将会使热带东印度洋—西太平洋海表温度偏高、外逸长波辐射偏小、降水增多,凝结潜热释放增强,产生偏强的东亚Hadley环流,使华南地区存在异常下沉运动,不利于产生降水;热带东印度洋—西太平洋海表温度偏高,还会使西北太平洋副热带高压位置偏西、面积偏大,西北太平洋存在气旋性环流异常,使华南地区受偏北气流异常控制,从而削弱了向华南地区的水汽输送。热带东印度洋—西太平洋海表温度年代际变化是热带西印度洋热含量异常影响华南秋旱年代际变化的重要环节,因此用NCAR CAM5.1全球大气环流模式进行了热带东印度洋—西太平洋海表温度年代际变化的敏感性试验,证实该区海表温度年代际升高对华南秋季年代际干旱具有重要作用。     

1960-2013年艾比湖绿洲湿地潜在蒸散量及地表湿润度变化特征分析

基于阿拉山口、精河、博乐、温泉4个气象站点1960-2013年地面观测气象数据,采用Penman-Monteith公式、Mann-Kendall检验、小波分析、主成分相关分析等方法分析艾比湖绿洲湿地年及季节潜在蒸散量及地表湿润度的特征变化及定量化成因,以期为艾比湖绿洲湿地区域的水资源科学配置提供科学依据。结果表明：（1）1960-2013年,艾比湖绿洲湿地年平均潜在蒸散量为1 063.52mm,夏季值最大为552.3 mm,冬季最小为25.3 mm,年平均潜在蒸散量以12.68 mm·（10a）^-1的速率递减,各季节潜在蒸散变化趋势与年变化一致,夏季表现最明显;（2）Mann-Kendall检验表明,年均和春、夏、秋潜在蒸散量显著性突变时间分别是1991年、1994年、1994年和1993年,冬季不存在突变,显著性突变均发生在21世纪90年代,地表湿润度年突变时间为1985年;（3）艾比湖绿洲湿地潜在蒸散量及地表湿润度存在明显的周期变化,主震荡周期分别为29 a和21 a,以多、少交替发生,具有全域性;（4）风速是年及季节潜在蒸散量的主导因素,地表湿润度变化的主导因素是降水量和相对湿度。     

阿克苏河流域气候变化对潜在蒸散量影响分析

蒸散发是水文过程的关键环节,研究气候因子对潜在蒸散发的影响,有助于深入认识水文过程对气候变化的响应。本文基于阿克苏河流域1960-2007 年逐日气象资料和Penman-Monteith公式,估算并分析参考作物蒸散量(RET) 时空变化特征,并用多元回归方法定量区分气候因子变化对RET 变化的贡献率。研究发现流域RET 空间差异明显,东部平原区平均年RET 为1100mm左右,是西部山区的近2 倍;东南部绿洲区的RET显著减少,而西部变化复杂。RET变化趋势的季节差异也很显著,以夏季变幅最大,是年变化的主要贡献者。高海拔地区相对湿度对RET变化影响最大,其它区域的风速变化对RET变化的贡献率最高。库车和乌恰站的风速变化对RET变化的贡献率大于50%,是RET变化的主导因素。     

Ensemble simulation of land evapotranspiration in China based on a multi-forcing and multi-model approach

In order to reduce the uncertainty of offline land surface model(LSM) simulations of land evapotranspiration(ET), we used ensemble simulations based on three meteorological forcing datasets [Princeton, ITPCAS(Institute of Tibetan Plateau Research, Chinese Academy of Sciences), Qian] and four LSMs(BATS, VIC, CLM3.0 and CLM3.5), to explore the trends and spatiotemporal characteristics of ET, as well as the spatiotemporal pattern of ET in response to climate factors over mainland China during 1982–2007. The results showed that various simulations of each member and their arithmetic mean(Ens Mean) could capture the spatial distribution and seasonal pattern of ET sufficiently well, where they exhibited more significant spatial and seasonal variation in the ET compared with observation-based ET estimates(Obs MTE). For the mean annual ET, we found that the BATS forced by Princeton forcing overestimated the annual mean ET compared with Obs MTE for most of the basins in China, whereas the VIC forced by Princeton forcing showed underestimations. By contrast, the Ens Mean was closer to Obs MTE, although the results were underestimated over Southeast China. Furthermore, both the Obs MTE and Ens Mean exhibited a significant increasing trend during 1982–98; whereas after 1998, when the last big EI Ni ?no event occurred, the Ens Mean tended to decrease significantly between 1999 and 2007, although the change was not significant for Obs MTE. Changes in air temperature and shortwave radiation played key roles in the long-term variation in ET over the humid area of China, but precipitation mainly controlled the long-term variation in ET in arid and semi-arid areas of China.     

数据驱动的蒸散发遥感反演方法及产品研究进展

蒸散发是水圈、大气圈和生物圈中水分循环和能量交换的纽带。在全球尺度上,蒸散发约占陆地降水总量的60%;作为其能量表达形式,潜热通量约占地表净辐射的80%。随着通量观测技术的发展,全球长期持续的观测数据得以获取和共享,近年来基于数据驱动的蒸散发遥感反演方法取得了较好的研究进展。本文针对数据驱动的蒸散发遥感反演方法和产品,从经验回归、机器学习和数据融合3个方面展开,对现有的研究进展进行了梳理、归纳和总结,并从驱动数据、反演方法、已有产品等方面指出目前仍存在的问题和不足。未来仍需开展数据驱动的高时空分辨率的蒸散发遥感反演方法的研究,有效考虑地表温度和土壤水分等可以指示地表蒸散发短期变化的重要信息,同时加强基于过程驱动的物理模型与数据驱动的模型的结合,使两类模型能互为补充、各自发挥所长,共同推动蒸散发遥感反演研究水平的进步。     

西北中部半干旱区兴隆山森林岛降水机理的数值模拟

通过WRF V2.1.2模式数值模拟试验并结合长期观测数据,研究了中国西北半干旱区长期存在和维持的森林山区(兴隆山区,103.84°E、35.86°N)的降水特征及其与周边地区的降水差异,并探讨了造成这种差异的主要原因。结果表明,兴隆山区与周边地区的降水差异主要表现在夏、秋季。在夏、秋季兴隆山区受东南湿润气流的影响,获得较多的水汽输入和较稳定的水汽来源,而山地地形则有利于截留东南气流携带的水汽并形成降水;兴隆山区及其周边地区局地的蒸散差异对二者之间降水差异的贡献不大。另外,兴隆山区土壤堆积覆盖的石质山构造和森林下垫面也有利于降水的截留和贮存以及植被的生长。因此,有利于水汽输入的大尺度环流形势、地形对空中水汽的截留以及特殊的地质因素是兴隆山山区孤立森林岛在半干旱区长期存在和维持的原因。     

Water status in winter wheat grown under salt stress

1 IntroductionSalinization is one of the major problems in arid and semi-arid regions in relation to land use and in particular to agricultural production[1]. Excessive salinity leads to toxicity in crops and reduction of the availability of water to crops, by reducing the osmotic potential of the soil solution[2]. Movement of soil water induces solute transport, and solutes are transferred towards the ground surface by the upward soil-water movement caused by evaporation, resulting in an accu…     

贡嘎山东坡亚高山森林区蒸散力的估算

以海螺沟 30 0 0m气象站的观测资料为基础 ,运用Penman公式法　空气饱和差法和桑斯维特公式法 ,计算了贡嘎山东坡亚高山林林的年平均蒸散力 ,其结果为分别为 431 81mm、171 4mm和 44 6 4mm。通过分析蒸散力的影响因素 ,对这三种计算蒸散力的方法作了比较 ,对计算结果存在的差异作了比较合理的解释 ,认为用Penman公式法可以估计出本研究区的蒸散力。同时 ,对蒸散力及其影响因自进行了相关分析 ,指出湿度和风不是速制约研究区蒸散力的主导因子 ,并分析了蒸散力与水面蒸发的关系 ,由此推导出估算蒸散力的简便方程 :PE =6 6 77 0 6 91E60 1 0 75 1ITm 0 0 396Pm。     

Seasonal climate patterns and their influence on calibration of the Hargreaves-Samani equation

Abstract

Annual patterns in climate parameters were studied to evaluate how these influence the quality of reference evapotranspiration (ETo) estimates obtained from the Hargreaves-Samani (HS) equation, since the method only uses the measured temperature directly. The work evaluates how these patterns can be used to improve the HS ETo estimates. Ten-year moving averages from a set of California Irrigation Management Information System (CIMIS) stations were used to evaluate the relationships between solar radiation (R_s), temperature (T) and ETo. The results indicate that T treads behind solar radiation and its value peaks some 25 days later. Thus, the main irrigation season in the Mediterranean climate (1 May–30 September) can be divided into three phases: increasing R_s and T; decreasing R_s with increasing T; and decreasing R_s and T. Non-univocal annual cycles were observed between R_s and T, ETo and R_s, and ETo and T. These annual patterns result in important seasonal changes in the ratio between the HS and Penman-Monteith (FAO PM) ETo estimates. The changes are particularly important during the irrigation season, where the FAO PM initially calculates greater ETo values than the HS methodology, and from the end of May to early September, where the HS equation overestimates the ETo values (by 17 mm, or 3%). These patterns obtained from 2000–2009 data were used to calibrate and improve HS ETo estimates at new sites for the 2010–2011 period. Calibration based on the proposed seasonal region-wide FAO PM/HS ETo ratios improved both the bias (decreased from 0.40 to 0.36 mm d^-1) and r² (increased from 0.67 to 0.87) of the ETo estimates for the irrigation season. The proposed methodology can be easily applied to other regions, even when the existing weather stations are sparse.

Editor Z.W. Kundzewicz