Rainstorm Magnitude Likely Regulates Event Water Fraction and Its Transit Time in Mesoscale Mountainous Catchments: Implication for Modelling Parameterization

oleh: Jun-Yi Lee, Yu-Ting Shih, Chiao-Ying Lan, Tsung-Yu Lee, Tsung-Ren Peng, Cheing-Tung Lee, Jr-Chuan Huang

Format: Article
Diterbitkan: MDPI AG 2020-04-01

Deskripsi

Event water transit time estimation has rarely been done for violent rainstorms (e.g., typhoons) in steep and fractured mountainous catchments where the range of transit time, potential controlling factors, and the validity of time-invariant parametrization are unclear. Characterized by steep landscape and torrential typhoon rainfall, Taiwan provides great opportunities for inquiring into the above questions. In this study, the hydrometrics and δ<sup>18</sup>O in rainwater and streamwater were sampled with a ~3-h interval for six typhoon events in two mesoscale catchments. The TRANSEP (transfer function hydrograph separation) model and global sensitivity analysis were applied for estimating mean transit time (MTT<sub>ew</sub>) and fraction (F<sub>ew</sub>) of event water and identifying the chronosequent parameter sensitivity. Results showed that the MTT<sub>ew</sub> and F<sub>ew</sub> varied from 2.0 to 11.0 h and from 0.2 to 0.8, respectively. Our MTT<sub>ew</sub> in the mesoscale catchments is comparable with that in microscale catchments, showing a fast rainfall-runoff transfer in our steep catchments. The average rainfall intensity is a predominant indicator, which negatively affects the MTT<sub>ew</sub> and positively affects the F<sub>ew</sub>, likely activating preferential flow-paths and quickly transferring event water to the stream. Sensitivity analysis among inter- and intra-events demonstrates that parameter sensitivity is event-dependent and time-variant. A quick and massive subsurface flow without distinct mixing with groundwater would be triggered during large rainstorms, suggesting that time-variant parameterization should be particularly considered when estimating the MTT<sub>ew</sub> in steep and fractured catchments at rainstorm scale.