Fluxes all of the time? A primer on the temporal representativeness of FLUXNET
Fluxes all of the time? A primer on the temporal representativeness of FLUXNET
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DOI：
10.1002/2016jg003576
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发表时间：
2017-02-01
影响因子：
3.7
通讯作者：
Reichstein, Markus
中科院分区：
文献类型：
--
作者：
Chu, Housen;Baldocchi, Dennis D.;Reichstein, Markus
FLUXNET是全球涡度相关通量塔网络，提供最大的CO2、H2O和能量通量综合数据集。为了实现“随时随地”提供通量信息的最终目标，研究试图解决代表性问题，即，在一组给定位置和测量周期中进行的测量是否可以外推到空间和时间明确的程度（例如，地球仪，1982-2013年气候基线）。本研究的重点是FLUXNET的时间代表性和测试是否站点特定的测量周期是足以捕捉气候和生物条件的自然变异。FLUXNET在测量长度和时间外推潜力方面在各地点的代表性不均匀。各年驾驶员条件的相似性一般使通量信息的外推超出测量周期。然而，这种外推的潜力进一步受到现场的具体变化的驱动程序的条件。若干驱动变量，如气温、昼夜温差、潜在蒸散量和归一化差异植被指数，在基线期内有可检测的趋势和/或断点，通量测量一般涵盖这些驱动变量中的类似和有偏差的条件。大约38%和60%的FLUXNET站点分别对所有驱动条件的平均条件和年际变化进行了充分采样。对于长期记录的网站（>= 15年），百分比分别增加到59%和69%。然而，时间代表性的理由不应仅仅依赖于测量的长度。在可能的情况下，应考虑场地的具体情况（例如，趋势、转折点和驱动因素的年际变化）。
FLUXNET, the global network of eddy covariance flux towers, provides the largest synthesized data set of CO2, H2O, and energy fluxes. To achieve the ultimate goal of providing flux information '' everywhere and all of the time,'' studies have attempted to address the representativeness issue, i.e., whether measurements taken in a set of given locations and measurement periods can be extrapolated to a space-and time-explicit extent (e.g., terrestrial globe, 1982-2013 climatological baseline). This study focuses on the temporal representativeness of FLUXNET and tests whether site-specific measurement periods are sufficient to capture the natural variability of climatological and biological conditions. FLUXNET is unevenly representative across sites in terms of the measurement lengths and potentials of extrapolation in time. Similarity of driver conditions among years generally enables the extrapolation of flux information beyond measurement periods. Yet such extrapolation potentials are further constrained by site-specific variability of driver conditions. Several driver variables such as air temperature, diurnal temperature range, potential evapotranspiration, and normalized difference vegetation index had detectable trends and/or breakpoints within the baseline period, and flux measurements generally covered similar and biased conditions in those drivers. About 38% and 60% of FLUXNET sites adequately sampled the mean conditions and interannual variability of all driver conditions, respectively. For long-record sites (>= 15 years) the percentages increased to 59% and 69%, respectively. However, the justification of temporal representativeness should not rely solely on the lengths of measurements. Whenever possible, site-specific consideration (e.g., trend, breakpoint, and interannual variability in drivers) should be taken into account.