# Ship Route Oil Spill Modeling: A Case Study of the Northeast Brazil Event, 2019
## 2 Materials and Methods
### Model Evaluation  
To evaluate the model outputs, we used a dataset comprising the latitudinal distribution of oil sightings along the coast between 31 August and 2 December 2019 (box plot analysis) provided by the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA). The total amount of oil that reached the coast during this period (approximately 5000 tons), the latitudinal distribution observed along the Brazilian coast, and the date and location of the first oil sighting (30 August in the southern part of the state of Paraiba (PB), around 7\({}^{\circ}\)33\({}^{\prime}\) S and 34\({}^{\circ}\)49\({}^{\prime}\) W) were also used as parameters to assess the results of the 31 simulations conducted for ships en route near the area of interest between July and August 2019. To incorporate an additional experiment featuring observational data and well-known initial conditions (e.g., oil type, spill location, total spilled volume, duration, and date of the spill) to assess the representativeness of the OSCAR results, we used the case study of the floating production unit (FPU) P-53 located 120 km off the coast of the State of Rio de Janeiro (RJ). The initial conditions used for the simulation were obtained from the Accident Investigation Report made available by IBAMA, and the summary settings can be found in Table 4. The meteo-oceanographic forcings were the same as those used in the oil tanker experiments (CMEMS and ERA5). We selected this well-documented case study due to the availability of sufficient data and information that could be utilized in the oil dispersion model and the assessment of results. In the future, additional case studies using meteo-oceanographic forcings with higher resolution could be used to enhance the evaluation of the OSCAR simulation results within Brazilian jurisdictional waters. The evaluation of the model results was based on the observation of the arrival of oil from the P-53 platform in the northern coastal region of Rio de Janeiro, near the beaches of Arraial do Cabo, Buzios, and Cabo Frio, around 22.875\({}^{\circ}\) S and 41.964\({}^{\circ}\) W between 3 and 4 April 2019, approximately 10 to 11 days after the onset of the spill. It is noteworthy that the horizontal resolution of CMEMS is considered low for the analysis of dynamic oceanographic processes in shallow waters over the inner continental shelf, especially on a \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Number of liquid/solid particles & 2000 \\ X direction resolution (m) & 2980 \\ Y direction resolution (m) & 2900 \\ Z direction layers & 10 \\ Maximum concentration grid depth (m) & 1000 \\ Oil type & Heavy bunker \\ \({}^{\circ}\)API oil & 14 \\ Viscosity (cP) & 28,000 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Model setting. scale of hundreds of meters to a few kilometers between one beach and another; however, it allows for a general analysis of the spatiotemporal representativeness of the oil's arrival. The results are shown in Figure 2.  
The model results indicated that the oil reached the coast on April 1 in the same region where it was actually observed, i.e., near the beaches of Arraai do Cabo (RJ), approximately two days prior to the observation. The analysis demonstrated that the ocean circulation system over the continental shelf, driven by a change in wind direction between 30 March and 1 April (see the stick plot in the lower panel), played a significant role in the fate of the surface oil by carrying it toward the coast. Thus, considering the limitation in the resolution of the applied forcings, the model was able to represent a realistic case study that occurred in 2019.