Preprints
https://doi.org/10.5194/nhess-2021-157
https://doi.org/10.5194/nhess-2021-157

  04 Jun 2021

04 Jun 2021

Review status: this preprint is currently under review for the journal NHESS.

Temporal changes in rainfall intensity-duration thresholds for post-wildfire flash floods and sensitivity to spatiotemporal distributions of rainfall

Tao Liu1,2, Luke A. McGuire1, Nina Oakley3, and Forest Cannon3 Tao Liu et al.
  • 1Department of Geosciences, University of Arizona, Tucson, AZ 85721-0011, USA
  • 2Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721-0011, USA
  • 3Center for Western Weather and Water Extremes, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA

Abstract. Rainfall intensity-duration (ID) thresholds are commonly used to assess flash flood potential downstream of burned watersheds. High-intensity and/or long-duration rainfall is required to generate flash floods as landscapes recover from fire, but there is little guidance on how thresholds change as a function of time since burning. Here, we force a hydrologic model with radar-derived precipitation to estimate ID thresholds for post-fire flash floods in a 41.5 km2 watershed in southern California, USA. Prior work in this study area constrains temporal changes in hydrologic model parameters, allowing us to estimate temporal changes in ID thresholds. Results indicate that ID thresholds increase by more than a factor of 2 from post-fire year 1 to post-fire year 5. Thresholds based on averaging rainfall intensity over durations of 30–60 minutes perform better than those that average rainfall intensity over shorter time intervals. Moreover, thresholds based on the 75th percentile of radar-derived rainfall intensity over the watershed perform better than thresholds based on the 25th or 50th percentile of rainfall intensity. Results demonstrate how hydrologic models can be used to estimate changes in ID thresholds following disturbance and provide guidance on the rainfall metrics that are best suited for predicting post-fire flash floods.

Tao Liu et al.

Status: open (until 16 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on nhess-2021-157', Anonymous Referee #1, 10 Jun 2021 reply

Tao Liu et al.

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Short summary
A well-constrained rainfall-runoff model forced by radar-derived precipitation is used to define rainfall intensity-duration (ID) thresholds for flash flood. The rainfall ID doubles in five years after a severe wildfire in a watershed in southern California, USA. Rainfall ID perform stably well when the intense pulses of rainfall over durations of 30–60 minutes that cover at least 15 %–25 % of the watershed. This finding could help issuing flash flood warnings based on radar-derived precipitation.
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