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首页> 外文期刊>Hydrology and Earth System Sciences Discussions >Reevaluation of transit time distributions, mean transit times and their relation to catchment topography
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Reevaluation of transit time distributions, mean transit times and their relation to catchment topography

机译：重新评估渡越时间分布，平均渡越时间及其与集水区地形的关系

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pstrongAbstract./strong The transit time of water is a fundamental property of catchments, revealing information about the flow pathways, source of water and storage in a single integrated measure. While several studies have investigated the relationship between catchment topography and transit times, few studies expanded the analysis to a wide range of catchment properties and assessed the influence of the selected transfer function (TF) model. We used stable water isotopes from mostly baseflow samples with lumped convolution models of time-invariant TFs to estimate the transit time distributions of 24 meso-scale catchments covering different geomorphic and geologic regions in Switzerland. The sparse network of 13 precipitation isotope sampling sites required the development of a new spatial interpolation method for the monthly isotopic composition of precipitation. A point-energy-balance based snow model was adapted to account for the seasonal water isotope storage in snow dominated catchments. Transit time distributions were estimated with three established TFs (exponential, gamma distribution and two parallel linear reservoirs). While the exponential TF proved to be less suitable to simulate the isotopic signal in most of the catchments, the gamma distribution and the two parallel linear reservoirs transfer function reached similarly good model fits to the fortnightly observed isotopic compositions in discharge, although in many catchments the transit time distributions implied by equally well fitted models differed markedly from each other and in extreme cases, the resulting mean transit time (MTT) differed by orders of magnitude. A more thorough comparison showed that equally suited models corresponded to agreeing values of cumulated transit time distributions only between 3 and 6 months. The short-term ( 30 days) component of the transit time distributions did not play a role because of the limited temporal resolution of the available input data. The long-term component ( 3 years) could hardly be assessed by means of stable water isotopes, resulting in ambiguous MTT and hence questioning the relevance of an MTT determined with stable isotopes. Finally we investigated the relation between MTT estimates based on the three different TF types as well as other transit time properties and a range of topographical catchment characteristics. Depending on the selected transfer model, we found a weak correlation between transit time properties and the ratio between flow path length over the flow gradient, drainage density and the mean discharge. The catchment storage derived from MTTs and mean discharge did not show a clear relation to any catchment properties, indicating that in many studies the mean annual discharge may bias the MTT estimates./p.
机译：> >摘要。水的流转时间是流域的一项基本属性，它以单一的综合方式揭示了有关流路，水源和储水的信息。尽管有几项研究调查了流域地形和渡越时间之间的关系，但很少有研究将分析扩展到广泛的流域性质并评估所选传递函数（TF）模型的影响。我们使用时基TF的集总卷积模型对大部分基流样品的稳定水同位素进行了估算，以估算覆盖瑞士不同地貌和地质区域的24个中尺度集水区的穿越时间分布。 13个降水同位素采样点的稀疏网络要求开发一种新的空间插值方法，以计算降水的每月同位素组成。基于点能量平衡的积雪模型适用于解释积雪为主的流域中季节性水同位素的存储。用三个已建立的TF（指数，伽马分布和两个平行的线性储层）估算了运输时间分布。尽管事实证明，指数TF不太适合模拟大多数流域的同位素信号，但伽马分布和两个平行线性储层的传递函数达到了相似的良好模型，适合于每两周观察到的排放中的同位素组成，尽管在许多流域，同样拟合良好的模型所隐含的运输时间分布彼此之间也存在显着差异，在极端情况下，所得的平均运输时间（MTT）相差一个数量级。更彻底的比较表明，同样合适的模型仅在3到6个月之间对应累积的运输时间分布的一致值。由于可用输入数据的时间分辨率有限，运输时间分布的短期（<30天）部分没有发挥作用。很难通过稳定的水同位素来评估长期成分（> 3年），从而导致MTT模棱两可，因此质疑了用稳定同位素确定的MTT的相关性。最后，我们研究了基于三种不同TF类型以及其他渡越时间特性和一系列地形汇水特征的MTT估算值之间的关系。根据所选的传递模型，我们发现渡越时间特性与流径长度对流量梯度的比值，排水密度和平均流量之间的相关性较弱。来自MTTs和平均排放量的集水量存储与任何集水性质均没有明确的关系，这表明在许多研究中，平均年排放量可能会偏离MTT估计值。。

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