Preprints
https://doi.org/10.5194/hess-2024-36
https://doi.org/10.5194/hess-2024-36
06 Mar 2024
 | 06 Mar 2024
Status: this preprint is currently under review for the journal HESS.

Bimodal Hydrographs in Semi-humid Forested Watershed: Characteristics and Occurrence Conditions

Zhen Cui, Fuqiang Tian, Zilong Zhao, Zitong Xu, Yongjie Duan, Jie Wen, and Mohd Yawar Ali Khan

Abstract. Bimodal runoff behavior, characterized by two distinct peaks in flow response, often leads to significant stormflow and associated flooding. Understanding and characterizing this phenomenon is crucial for effective flood forecasting. However, this runoff behavior has been understudied and poorly understood in semi-humid regions. In this study, we investigated the response characteristics and occurrence conditions of bimodal hydrograph based on the hydrometric and isotope data spanning 10 years in a semi-humid forested watershed in North China. The main findings include: 1) the onset of the bimodal hydrograph exhibits a threshold behavior, with delayed streamflow peaks occurring when the sum of event rainfall (P) and antecedent soil moisture index prior to the rainfall (ASI) exceeds 200 mm; 2) isotopic hydrograph separation reveals that delayed stormflow process is primarily driven by pre-event water, with increasing contributions of pre-event water during catchment wetting-up; 3) the dynamic variation in groundwater level precedes that of streamflow, establishing a hysteretic relationship wherein groundwater level peaks before streamflow during delayed stormflow. These findings, supported by onsite observations, emphasize the dominance of shallow groundwater flow in the generation of delayed stormflow.

Zhen Cui, Fuqiang Tian, Zilong Zhao, Zitong Xu, Yongjie Duan, Jie Wen, and Mohd Yawar Ali Khan

Status: open (until 01 May 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2024-36', Anonymous Referee #1, 19 Mar 2024 reply
    • AC1: 'Reply on RC1', Zhen Cui, 05 Apr 2024 reply
  • RC2: 'Comment on hess-2024-36', Anonymous Referee #2, 01 Apr 2024 reply
    • AC2: 'Reply on RC2', Zhen Cui, 05 Apr 2024 reply
Zhen Cui, Fuqiang Tian, Zilong Zhao, Zitong Xu, Yongjie Duan, Jie Wen, and Mohd Yawar Ali Khan
Zhen Cui, Fuqiang Tian, Zilong Zhao, Zitong Xu, Yongjie Duan, Jie Wen, and Mohd Yawar Ali Khan

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Short summary
We investigated the response characteristics and occurrence conditions of bimodal hydrograph based on the hydrometric and isotope data spanning 10 years in a semi-humid forested watershed in North China. We found that the bimodal hydrograph occurs when the sum of event rainfall and antecedent soil moisture index prior to the rainfall exceeds 200 mm, and delayed stormflow is mainly contributed by shallow groundwater.