A Statistical Method for Generating Temporally Downscaled Geochemical Tracers in Precipitation
A Statistical Method for Generating Temporally Downscaled Geochemical Tracers in Precipitation
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DOI：
10.1175/jhm-d-20-0142.1
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发表时间：
2021-06-01
影响因子：
3.8
通讯作者：
Bowen, Gabriel J.
中科院分区：
文献类型：
--
作者：
Finkenbiner, Catherine E.;Good, Stephen P.;Bowen, Gabriel J.
降水地球化学测量的采样间隔通常比精细尺度水文气象模型所需的间隔更粗。这项研究提出了一种统计方法，以时间尺度下的地球化学示踪剂信号在降水，使它们可以用于高分辨率，示踪剂启用的应用程序。在该方法中，我们分离的时间序列的确定性成分和其余的日常随机成分，这是近似的条件多元高斯分布。具体而言，统计的随机组成部分可以解释从粗糙的数据，使用新确定的幂律衰减函数，它涉及到数据聚合间隔的变化示踪剂浓度方差和相关性与降水量。这些统计数据中使用的Copula框架生成合成示踪剂值的确定性和随机时间序列的组成部分的基础上，每天的降水量。该方法在全球27个地点进行了评估，使用每日降水同位素比值，及时汇总，以提供具有已知每日值的低分辨率测试数据集。在每个站点，降尺度方法应用于每周、每两周和每月的汇总系列，以产生每日示踪剂实现的集合。相对于观测结果，从每两周一次的系列中缩小的每日示踪剂浓度的平均（+/-标准差）绝对误差为：δ H-2为1.69千分之一（1.61千分之一），δ O-18为0.23千分之一（0.24千分之一）。结果表明，粗采样的降水示踪剂可以准确地缩小到每日值。这种方法可以扩展到其他地球化学示踪剂，以生成所需的驱动复杂的，精细尺度的水文气象过程模型的缩小规模的数据集。
Sampling intervals of precipitation geochemistry measurements are often coarser than those required by fine-scale hydrometeorological models. This study presents a statistical method to temporally downscale geochemical tracer signals in precipitation so that they can be used in high-resolution, tracer-enabled applications. In this method, we separated the deterministic component of the time series and the remaining daily stochastic component, which was approximated by a conditional multivariate Gaussian distribution. Specifically, statistics of the stochastic component could be explained from coarser data using a newly identified power-law decay function, which relates data aggregation intervals to changes in tracer concentration variance and correlations with precipitation amounts. These statistics were used within a copula framework to generate synthetic tracer values from the deterministic and stochastic time series components based on daily precipitation amounts. The method was evaluated at 27 sites located worldwide using daily precipitation isotope ratios, which were aggregated in time to provide low-resolution testing datasets with known daily values. At each site, the downscaling method was applied on weekly, biweekly, and monthly aggregated series to yield an ensemble of daily tracer realizations. Daily tracer concentrations downscaled from a biweekly series had average (+/- standard deviation) absolute errors of 1.69 parts per thousand (1.61 parts per thousand) for delta H-2 and 0.23 parts per thousand (0.24 parts per thousand) for delta O-18 relative to observations. The results suggest coarsely sampled precipitation tracers can be accurately downscaled to daily values. This method may be extended to other geochemical tracers in order to generate downscaled datasets needed to drive complex, fine-scale models of hydrometeorological processes.