Fraction of young water (Fyw) and mean transit time (MTT, τ) calculated from water isotope profiles are valuable information for catchment hydrological assessment, especially in anthropogenically impacted region where natural conditions may not be decisive to catchment hydrology. The calculation of Fyw and MTT were performed on three subsets of δ¹⁸O_H₂O data collected at the Hanoi meteo-hydrological station, Red River, in three periods; 2002–2005, 2015, and 2018–2019. The mean (min and max) values of δ¹⁸O_H₂O in rainwater over the three periods are, respectively, −5.3‰ (−11.0 and −1.2‰), −5.4‰ (−10.7 and −1.4‰), and −4.5‰ (−13.9 and 1.7‰). The corresponding values in river water are −8.4‰ (−9.8 and −6.9‰), −8.5‰ (−9.1 and −7.7‰), and −8.4‰ (−9.5 and −7.2‰), respectively. The mean of Fyw calculated from the δ¹⁸O_H₂O data for different periods is 22 ± 9%, 10 ± 5%, and 8 ± 3%. Mean transit time is 4.69 ± 15.57, 1.65 ± 1.53, and 2.06 ± 1.87 years. The calculated Fyw (MTT) is negatively (positively) proportional to change in reservoir volume over the three periods, which is logical, since reservoirs tend to keep more water in the catchment and slower down water flow. The strong variation of Fyw and τ, two essential variables characterizing the catchment hydrology, represents an anthropogenic impact in the Red River system.

中文翻译：

---

水稳定同位素在红河（亚洲）水文表征中的应用

根据水同位素剖面计算的年轻水的比例( Fyw ) 和平均传输时间 (MTT, τ) 是流域水文评估的宝贵信息，尤其是在自然条件可能对流域水文没有决定性作用的人为影响地区。Fyw和MTT的计算是对河内红河气象水文站三个时期收集的δ ¹⁸ O_H ₂ O数据的三个子集进行的；2002-2005、2015 和 2018-2019。δ ¹⁸ O_H ₂的平均值（最小值和最大值）三个时期雨水中的O分别为-5.3‰（-11.0‰和-1.2‰）、-5.4‰（-10.7‰和-1.4‰）和-4.5‰（-13.9‰和1.7‰）。河水中的对应值分别为-8.4‰（-9.8‰和-6.9‰）、-8.5‰（-9.1‰和-7.7‰）和-8.4‰（-9.5‰和-7.2‰）。由不同时期的δ ¹⁸ O_H ₂ O数据计算得到的Fyw平均值为22±9%、10±5%和8±3%。平均传输时间为 4.69 ± 15.57、1.65 ± 1.53 和 2.06 ± 1.87 年。计算出的Fyw (MTT) 与三个时期内水库容积的变化成负（正）比例，这是合乎逻辑的，因为水库往往会在集水区保留更多的水并减慢水流。Fyw的强变异 τ 是表征集水区水文特征的两个基本变量，代表红河系统中的人为影响。