Preprints
https://doi.org/10.5194/egusphere-2023-3064
https://doi.org/10.5194/egusphere-2023-3064
16 Jan 2024
 | 16 Jan 2024
Status: this preprint is open for discussion.

A simple approach to represent precipitation-derived freshwater fluxes into nearshore ocean models: an FVCOM4.1 case study

Krysten Rutherford, Laura Bianucci, and William Floyd

Abstract. High-resolution numerical ocean models can be used to help interpret sparse observations in the nearshore as well as to help understand the impacts of climate change and extreme events on these dynamically complex coastal areas. However, these high-resolution ocean models require inputs with comparably high resolution, which is particularly difficult to achieve for freshwater discharge. Here, we explored a simple rain-based hydrological model as inputs into a high-resolution (≳13 m) model of Quatsino Sound – a fjord system located on the northwest coast of Vancouver Island, British Columbia, Canada. Through a series of sensitivity tests using an application of the Finite Volume Community Ocean Model (FVCOM version 4.1), we found that model performance was hindered by the lack of knowledge of ungauged rivers and streams. In this case study, including the only major gauged river implied ignoring 538 other watersheds of various sizes and accounted for only about a quarter of the total estimated freshwater discharge. We found that including at least 60 % and ideally closer to 75–80 % of total freshwater fluxes gave similar model performance to including all possible 539 freshwater sources; in our model simulations, this percentage of freshwater flux meant including rivers with watersheds greater than 20–50 km2, or 7–19 total rivers. Further sensitivity tests also indicated that knowing the main outpour locations into the nearshore ocean is an important factor, but not as important as the total freshwater discharge included. Overall, this study illustrates the complexities of studying the land-ocean connection and offers a simple and accessible tool to help address a common problem in nearshore modelling.

Krysten Rutherford, Laura Bianucci, and William Floyd

Status: open (until 12 Mar 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CEC1: 'Comment on egusphere-2023-3064', Juan Antonio Añel, 26 Jan 2024 reply
    • AC1: 'Reply on CEC1', Krysten Rutherford, 26 Jan 2024 reply
    • AC2: 'Reply on CEC1', Krysten Rutherford, 01 Feb 2024 reply
  • RC1: 'Comment on egusphere-2023-3064', Anonymous Referee #1, 14 Feb 2024 reply
Krysten Rutherford, Laura Bianucci, and William Floyd
Krysten Rutherford, Laura Bianucci, and William Floyd

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Short summary
Nearshore ocean models often lack complete information about freshwater fluxes due to numerous ungauged rivers and streams. We tested a simple rain-based hydrological model as inputs into an ocean model of Quatsino Sound, B.C., Canada with the aim of improving the representation of the land-ocean connection in the nearshore model. Through multiple tests, we found that the performance of the ocean model improved when providing 60 % or more of the freshwater inputs from the simple runoff model.