Investigating young water fractions in a small Mediterranean mountain catchment: Both precipitation forcing and sampling frequency matter
Investigating young water fractions in a small Mediterranean mountain catchment: Both precipitation forcing and sampling frequency matter
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DOI：
10.1002/hyp.13806
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发表时间：
2020-01
影响因子：
3.2
通讯作者：
F. Gallart;M. Valiente;P. Llorens;C. Cayuela;M. Sprenger;J. Latron
中科院分区：
文献类型：
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作者：
F. Gallart;M. Valiente;P. Llorens;C. Cayuela;M. Sprenger;J. Latron
在流域水文学中，对小于2 - 3个月的水的比例（年轻水部分，Fyw）的研究越来越多。Fyw通常通过比较降水和径流中的季节性示踪剂循环来估计，通过水采样。然而，一些开放的研究问题仍然存在，如：（一）是否应放弃夏季降水的一部分，因为高蒸散量的需求，（二）如何以及Fyw作为一个度量比较集水区，以及（iii）采样频率如何影响Fyw估计。为了解决这些问题，我们调查了Fyw在土壤-，地面-和流沃茨的小地中海可以维拉集水区。降雨量以5 mm的间隔取样。每两周对移动的土壤水和地下水进行取样。根据不同的时间间隔（30分钟至1周）的流量，对河水进行采样。在58个月的时间里，这次采样提供了1,529个δ 18 O测定结果。同位素分析结果使我们在输入信号中包括夏季降水。我们发现最高的Fyw在移动的土壤沃茨（34%），而这几乎是零地下水，除了在潮湿的时期。对于溪流沃茨，Fyw取决于流量变化，因此流量加权的年轻水比例（Fyw *）为22.6%，而时间加权的Fyw仅为6.2%。当调查不同的12个月采样期时，Fyw * 及其放电灵敏度（Sd）均不同。年轻的水部分，将获得一个虚拟的彻底采样（Fyw **）估计从Sd和观察到的流流量。这表明，由于遗漏了高流量，频繁动态采样低估了25%的Fyw **，每周采样低估了66%。我们的研究结果证实，Fyw和它的放电灵敏度是非常敏感的气象强迫在分析期间的指标。因此，集水区之间的比较需要长期的年平均值及其变化。我们的研究结果也支持Fyw估计对采样率的依赖性，并显示了流量加权分析的优势。最后，集水周转调查应伴随着流量持续时间曲线的分析。
The proportion of water younger than 2–3 months (young water fraction, Fyw) has become increasingly investigated in catchment hydrology. Fyw is typically estimated by comparing seasonal tracer cycles in precipitation and streamflow, through water sampling. However, some open research questions remain, such as: (i) whether part of the summer precipitation should be discarded because the high evapotranspiration demand, (ii) how well Fyw serves as a metric to compare catchments, and (iii) how sampling frequency affects Fyw estimates. To address these questions, we investigated Fyw in soil‐, ground‐ and stream waters for the small Mediterranean Can Vila catchment. Rainfall was sampled at 5‐mm intervals. Mobile soil water and groundwater were sampled fortnightly. Stream water was sampled depending on flow at variable time intervals (30 min to 1 week). Over 58 months, this sampling provided 1,529 δ18O determinations. Isotopic analyses results led us to include summer precipitation in the input signal. We found the highest Fyw in mobile soil waters (34%), while this was almost zero for groundwater except during wet periods. For stream waters, Fyw depended on the discharge variations, so that the flow‐weighted young water fraction ( Fyw* ) was 22.6%, whereas the time‐weighted Fyw was just 6.2%. Both Fyw* and its discharge sensitivity (Sd) varied when different 12‐month sampling periods were investigated. The young water fraction that would be obtained from a virtual thorough sampling ( Fyw** ) was estimated from the Sd and the observed stream flow. This showed an underestimation of Fyw** by 25% for the frequent dynamic sampling and 66% for weekly sampling, due to missing high flows. Our results confirm that Fyw and its discharge sensitivity are metrics very sensitive to meteorological forcing during the analysed period. Thus, comparisons between catchments need long‐term mean annual values and their variability. Our findings also support the dependence of Fyw estimates on the sampling rate and show the advantages of flow‐weighted analysis. Finally, catchment water turnover investigations should be accompanied by the analysis of flow duration curves.