遥感估算地表蒸散发真实性检验研究进展

地表蒸散发是连接土壤—植被—大气连续体的纽带,结合遥感技术估算地表蒸散发已成为获取区域乃至全球尺度时空连续地表蒸散发量的有效手段。由于遥感估算地表蒸散发容易受到地表空间异质性和近地层气象条件复杂性的影响,在模型机理与变量参数化方案、输入数据和时间尺度扩展等方面存在不确定性,影响了其准确度的提高和应用范围的拓展,因此需要开展真实性检验。本文综述了当前遥感估算地表蒸散发(包括植被蒸腾和土壤蒸发)真实性检验研究的相关成果,重点归纳并总结了应用于遥感估算地表蒸散发真实性检验的直接检验法和间接检法的主要原理、适用性和优缺点,在此基础上阐述了当前遥感估算地表蒸散发真实性检验研究所面临的挑战。分析表明：由于地表空间异质性的普遍存在,遥感估算地表蒸散发真实性检验研究在理论和方法方面还受到诸多挑战,今后应打破地表蒸散发遥感产品真实性检验局限在均匀地表的传统思路,发展非均匀地表遥感估算地表蒸散发真实性检验的理论框架,包括地表水热状况空间异质性的度量、非均匀地表验证场的优化布设、非均匀下垫面地表蒸散发的多尺度观测试验、卫星像元/区域尺度地表蒸散发相对真值的获取、验证过程中的不确定性分析以及遥感估算地表蒸散发的实证研究等,并构建一个多源、多尺度、多方法、多层次的真实性检验技术流程,以期把遥感估算地表蒸散发真实性检验作为突破口,提升相应遥感产品的应用水平,推动定量遥感科学的发展。     

Measurements of transpiration in four tropical rainforest types of north Queensland,Australia

Transpiration of four different rainforest types in north Queensland, Australia, was determined using the heat pulse technique for periods ranging between 391 and 657 days. Despite the complexity of the natural rainforest systems being studied, the relationship between sample tree size and daily water use was found to be strong, thus providing a robust means by which to scale transpiration from individual trees to the entire forest stand. Transpiration was shown to be dependent on solar radiation and atmospheric demand for moisture with little evidence of limitation by soil moisture supply. Total stand transpiration was controlled by forest characteristics such as stem density, size distribution and sapwood area. Annual transpiration for each of the four sites ranged between 353 mm for cloud forest and 591 mm for montane rainforest. In comparison with the international literature, transpiration from Australian rainforests is low; the reasons for this could be related to a combination of differences in forest structure, climatic conditions, canopy wetness duration and tree physiology. Copyright © 2007 John Wiley & Sons, Ltd.     

温室内作物腾发量计算与验证

以彭曼-蒙特斯方程(简称P-M)为基础,根据温室内地表净辐射的规律,推导出了计算温室内地表净辐射公式,同时引进作物冠层高度,对P-M方程中与风速有关的空气动力学项进行修正,导出了适合于计算温室条件下参考作物腾发量的P-M公式(简称P-M-修)。对不同方法的计算值进行了分析比较,并应用试验资料对P-M-修给予了验证。结果表明,P-M-修与实测值较为吻合,累计值平均误差仅为9.1%。     

我国参考作物蒸散的空间分布和时间趋势

根据我国616个地面气象台站1975-2004年的观测资料,利用联合国粮农组织推荐的Penman-Monteith公式计算各年逐日、逐月参考作物蒸散值(ET0)和年总量.结果表明,我国参考作物蒸散多年平均值大多界于800～1 100 mm之间,西北地区高,东北地区低.1978年出现最大值,1993年出现最低值,青藏高原以东地区波动小,西北地区波动大.参考作物蒸散变化率在-30～30 mm·(10 a)-1之间,西部和长江流域地区显著下降,东部沿海、黄河中上游和东北显著上升.造成我国参考作物蒸散出现先降后增趋势的主要因素是日照时数(净辐射)和饱和差.     

Desiccation of a Clay by Grass,Bushes and Trees

After reviewing the past 60 years of research into the desiccation of clay soils by grass, bushes and trees as it affects shallow building foundations and roads pavements, it was concluded that most past research has been opportunistic and unplanned. Also, no attempt has been made to relate changes of soil water content to rainfall and rates of evapotranspiration. The paper reports the second stage of a sustained programme to observe and understand seasonal and annual changes of soil water content under grass and adjacent to bushes and trees. A 12 months set of two-monthly soil water content contours is presented together with the associated soil water balance, and a method is described for assessing evapotranspiration by bushes and trees by means of a solar energy balance.     

农田蒸散发量变化规律分析

根据冉庄水资源实验站大型地中蒸渗仪在种植小麦、玉米情况下的农田蒸散发量实测资料，分析了农田蒸散发量的时程及深度变化规律，提出了在实验条件下农田蒸散发量的数值范围。     

退化羊草草原的群落蒸发蒸腾

草原群落蒸发蒸腾是一个由多种因素综合影响的复杂问题。本文在天然羊草草原上,以畜群点为中心由外向内,选择退化程度不同的放牧空间梯度系列替代退化演替时间梯度系列,用土柱称重法进行群落蒸发蒸腾观测,深入分析了羊草草原退化群落蒸发蒸腾的变化规律。得出:天然羊草草原在土壤供水较为充足的情况下,随着放牧强度的增加,群落生物量减少,盖度减少,蒸腾减少,蒸发增加,但蒸散减少不明显。     

Sensitivity and uncertainty analysis of mesoscale model downscaled hydro‐meteorological variables for discharge prediction

Precipitation and Reference Evapotranspiration (ETo) are the most important variables for rainfall–runoff modelling. However, it is not always possible to get access to them from ground‐based measurements, particularly in ungauged catchments. This study explores the performance of rainfall and ETo data from the global European Centre for Medium Range Weather Forecasts (ECMWF) ERA interim reanalysis data for the discharge prediction. The Weather Research and Forecasting (WRF) mesoscale model coupled with the NOAH Land Surface Model is used for the retrieval of hydro‐meteorological variables by downscaling ECMWF datasets. The conceptual Probability Distribution Model (PDM) is chosen for this study for the discharge prediction. The input data and model parameter sensitivity analysis and uncertainty estimations are taken into account for the PDM calibration and prediction in the case study catchment in England following the Generalized Likelihood Uncertainty Estimation approach. The goodness of calibration and prediction uncertainty is judged on the basis of the p‐factor (observations bracketed by the prediction uncertainty) and the r‐factor (achievement of small uncertainty band). The overall analysis suggests that the uncertainty estimates using WRF downscaled ETo have slightly smaller p and r values (p= 0.65; r= 0.58) as compared to ground‐based observation datasets (p= 0.71; r= 0.65) during the validation and hence promising for discharge prediction. On the contrary, WRF precipitation has the worst performance, and further research is needed for its improvement (p= 0.04; r= 0.10). Copyright © 2013 John Wiley & Sons, Ltd.