Preprints
https://doi.org/10.5194/hess-2019-276
https://doi.org/10.5194/hess-2019-276

  16 Jul 2019

16 Jul 2019

Review status: this preprint was under review for the journal HESS but the revision was not accepted.

Characterization of event water fractions and transit times under typhoon rainstorms in fractured mountainous catchments: Implications for time-variant parameterization

Jun-Yi Lee1, Yu-Ting Shih1, Chiao-Ying Lan1, Tsung-Yu Lee2, Tsung-Ren Peng3, Cheing-Tung Lee1, and Jr-Chuan Huang1 Jun-Yi Lee et al.
  • 1Department of Geography, National Taiwan University, Taipei City, 10617, Taiwan
  • 2Department of Geography, National Taiwan Normal University, Taipei City, Taiwan
  • 3Department of Soil and Environmental Sciences, National Chung Hsing University, Taichung City, Taiwan

Abstract. Transit time with its indicative significance in regulating rainfall-runoff mechanism is a key factor for understanding many biogeochemical processes, but is rarely investigated in steep and fractured mountainous catchments. Mountainous catchments in Taiwan are characterized by active endogenic tectonics and exogenic typhoons and thus provide opportunities to explore the hydrodynamic systems over time. In this study, the hydrometrics and δ18O in rain and stream water were sampled by ~ 3-hour interval for six typhoon events in two mesoscale catchments. The TRANSEP (transfer function hydrograph separation model) and global sensitivity analysis was applied for estimating mean transit time (MTTew) and fraction (Few) of event water and identifying the chronosequent parameter sensitivity. Results show that TRANSEP could satisfactorily simulate the streamflow and δ18O change with the efficiency coefficients of from 0.85 to 0.97 and from 0.61 to 0.99, respectively. The MTTew and Few varied from 2 to 11 h and from 0.2 to 0.8, respectively. Our MTTew in the meso-scale catchments is similar with that in micro-scale catchments, showing a fast transfer in our steep catchments. The mean rainfall intensity which negatively controls on the MTTew and positively on the Few is a predominant indicator which likely activates preferential flow paths and quickly transfers event water to the stream. Sensitivity analysis among inter- and intra-events suggested that parameter sensitivity is event-depend and time-variant, affirming a nonlinear behavior in event water transfer function and time-variant parameterization should be particularly considered when estimating the MTTew in steep and fractured catchments.

Jun-Yi Lee et al.

 
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Jun-Yi Lee et al.

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Short summary
Scientists concern the travel time and the fraction of new water from the sky to the stream to figure out the sources of freshwater and the distribution of contaminants. This study tells a story of water by analyzing the oxygen isotope of rain and stream water. In our sites, a raindrop only needs 2–11 hour to travel to the stream and large storm could exert more and younger new water. The rapid response is likely because of the steep landscape which helps transferring new water to the stream.