Calibration and Evaluation of WRF-Hydro Modeling System for Extreme Runoff Simulations: Use of High-Resolution Sea Surface Temperature (SST) Data

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2022-2
Kılıçarslan, Berina Mina
This study investigates the impact of the spatio-temporal accuracy of four different sea surface temperature (SST) datasets on the accuracy of the Weather Research and Forecasting (WRF)-Hydro system to simulate hydrological response during two catastrophic flood events over the Eastern Black Sea (EBS) and the Mediterranean (MED) regions of Turkey. Three daily-updated and high spatial resolution external SST products (GHRSST, Medspiration, and NCEP-SST) and one coarse-resolution and time-invariant SST product (ERA5- and GFS-SST for EBS and MED regions, respectively) already embedded in the initial and the boundary conditions datasets of WRF model are used in deriving near-surface atmospheric variables through WRF. Event-based calibration is performed to the WRF-Hydro system using hourly and daily streamflow data in both regions. Two different calibration methods, namely step-wise and automated calibration, are applied for the calibration process. Dynamically Dimensioned Search (DDS) Algorithm is utilized as the automated calibration algorithm to investigate the improvements in hydrograph simulations alternative to the step-wise approach. The uncoupled model simulations for independent SST events are conducted to assess the impact of SST-triggered precipitation on simulated extreme runoff. Despite the fact that manual calibration shows better performance with fewer iteration numbers, results show that the process-based automated calibration approach considering the impact of parameters on the hydrological behavior exhibits a promising performance, particularly in the EBS region. Some localized and temporal differences in the occurrence of the flood events with respect to observations depending on the SST representation are noticeable. SST products represented with higher cross-correlations (GHRSST and Medspiration) revealed significant improvement in flood hydrographs for both regions. The GHRSST dataset shows a substantial improvement in NSE (~70%) and KGE (from 0.06 to 0.3) with respect to the invariable SST (ERA5) in simulated runoffs over the EBS region. Reduction in RMSE up to 20% and an increase in correlation from 0.3 to 0.8 is observed for the same region. The use of both GHRSST and Medspiration SST data characterized with high spatio-temporal correlation resulted in runoff simulations exactly matching the observed runoff peak of 300 m3/s by reducing the overestimation seen in invariable SST (GFS) in the MED region. In addition, the KGE values are increased from 0.1 to 0.3 for the hydrographs generated with high-resolution SST simulations. Improved precipitation simulation skills of the WRF model with the detailed SST representation show that the hydrographs of GHRSST and Medspiration simulations show better performance compared to the simulated hydrographs by observed precipitation.

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Citation Formats
B. M. Kılıçarslan, “Calibration and Evaluation of WRF-Hydro Modeling System for Extreme Runoff Simulations: Use of High-Resolution Sea Surface Temperature (SST) Data,” M.S. - Master of Science, Middle East Technical University, 2022.