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Volume 11, issue 3 | Copyright
Geosci. Model Dev., 11, 903-913, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Development and technical paper 09 Mar 2018

Development and technical paper | 09 Mar 2018

Autocalibration of a one-dimensional hydrodynamic-ecological model (DYRESM 4.0-CAEDYM 3.1) using a Monte Carlo approach: simulations of hypoxic events in a polymictic lake

Liancong Luo1, David Hamilton2, Jia Lan3, Chris McBride4, and Dennis Trolle5 Liancong Luo et al.
  • 1State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China
  • 2Australian Rivers Institute, Griffith University, Queensland, Australia
  • 3Chunan Environmental Protection Bureau, Chunan, 311700, Zhejiang Province, China
  • 4Environmental Research Institute, Waikato University, Hamilton 3240, New Zealand
  • 5Department of Bioscience, Aarhus University, Aarhus 8000, Denmark

Abstract. Automated calibration of complex deterministic water quality models with a large number of biogeochemical parameters can reduce time-consuming iterative simulations involving empirical judgements of model fit. We undertook autocalibration of the one-dimensional hydrodynamic-ecological lake model DYRESM-CAEDYM, using a Monte Carlo sampling (MCS) method, in order to test the applicability of this procedure for shallow, polymictic Lake Rotorua (New Zealand). The calibration procedure involved independently minimizing the root-mean-square error (RMSE), maximizing the Pearson correlation coefficient (r) and Nash–Sutcliffe efficient coefficient (Nr) for comparisons of model state variables against measured data. An assigned number of parameter permutations was used for 10000 simulation iterations. The "optimal" temperature calibration produced a RMSE of 0.54°C, Nr value of 0.99, and r value of 0.98 through the whole water column based on comparisons with 540 observed water temperatures collected between 13 July 2007 and 13 January 2009. The modeled bottom dissolved oxygen concentration (20.5m below surface) was compared with 467 available observations. The calculated RMSE of the simulations compared with the measurements was 1.78mgL−1, the Nr value was 0.75, and the r value was 0.87. The autocalibrated model was further tested for an independent data set by simulating bottom-water hypoxia events from 15 January 2009 to 8 June 2011 (875 days). This verification produced an accurate simulation of five hypoxic events corresponding to DO < 2mgL−1 during summer of 2009–2011. The RMSE was 2.07mgL−1, Nr value 0.62, and r value of 0.81, based on the available data set of 738 days. The autocalibration software of DYRESM-CAEDYM developed here is substantially less time-consuming and more efficient in parameter optimization than traditional manual calibration which has been the standard tool practiced for similar complex water quality models.

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Short summary
We developed an autocalibration software for the hydrodynamic-ecological lake model DYRESM-CAEDYM with a massive number of water quality parameters, using a Monte Carlo sampling method, in order to reduce time-consuming iterative simulations with empirical judgements and find optimal model parameter set. The successful applications to Lake Rotorua suggest this software is much more efficient than traditional methods and of wide applicability to other water quality models.
We developed an autocalibration software for the hydrodynamic-ecological lake model...