# Ship Route Oil Spill Modeling: A Case Study of the Northeast Brazil Event, 2019
## 2 Materials and Methods  
The ship selection used in the oil spill simulations was based on the types of vessels that could have been transporting oil along the northeast coast of Brazil between April and August 2019. The selection of ships was based on their classification according to the type of cargo they carried, i.e., oil/chemical tanker, crude oil tanker, oil products tanker, shuttle tanker, chemical tanker, tanker, and bunkering tanker. During the selected period, 964 ships were identified in the Brazilian jurisdictional waters via the AIS data provided by the Brazilian Navy. The positions of the ships were filtered for those that were navigating within a region of interest. This region was defined as the polygon found in the study by [34] plus a surrounding area of up to 2 degrees (black polygon in Figure 1), which was identified as the most likely region of origin for the oil spill. Considering this delimited region and the same period, 200 ships were selected along 225 individual routes, with speeds ranging from 10 to 15 knots as they traversed two main maritime routes: northwest/southeast (approximately 135\({}^{\circ}\)) and northeast/southwest (approximately 220\({}^{\circ}\)). The ships comprised 31 Aframax (15.5%), 22 Panamax (11%), 26 Suezmax (13%), and 34 VLCC (17%), while the remaining 87 (43.5%) were small ships (i.e., smaller than Aframax) whose transported volume was likely to be insufficient to cause the environmental impact of 2019. Thus, the four selected types of oil tankers were the most representative vessels that crossed the region of interest within the specified period and were consequently utilized in the oil dispersion simulations.  
The total number of ships used in the simulation was further reduced to 31, comprising only those that navigated within the region of interest between July and August 2019. This remaining group of ships included Panamax (7), Aframax (9), Suezmax (6), and VLCC (9) vessels (colored routes in Figure 1). This time period was chosen as the most likely  
Figure 1: Oil tanker routes (Aframax, Panamax, Suezmax, and VLCC) close to the polygon of interest (black grid, ROI) between July and August 2019. The dashed green line represents the ship route used in experiment 22.  
timeframe during which the oil spill occurred at sea based on the distance of the routes from the coast and the mean speed of ocean currents in the region. The approximate dimensions of these vessels used for oil transportation were provided in [16] (Table 1).  
The total volume of oil used in the dispersion simulations considered the size of these vessels; however, without exact knowledge of the volume spilled into the sea, estimating the total spill volume could result in overestimation in the simulation results. It is known that oil production incurs significant costs, from exploration and transportation to refining and distribution; therefore, the scenario of a ship intentionally spilling its entire cargo into the sea is highly unlikely. Assuming that only a fraction of the total oil quantity was spilled into the sea, [13] estimated that a a plausible hypothesis is that the spill resulted from an accidental rupture of one or two internal tanks of these vessels, which would not compromise navigation safety. In the case of an intentional spill, the authors suggest that such a release could have been intentional to ensure safety, and the release rate would be consistent with the natural pumping of oil during the loading and unloading processes. For the dispersion simulations, the volume of two internal tanks and an average oil pumping rate of 4000 m\({}^{3}\) h\({}^{-1}\)[35] were considered (N.B. this value can vary from 2000 to 6000 m\({}^{3}\) h\({}^{-1}\), depending on the type of vessel and its operational characteristics [36]). By considering the leakage from two individual internal tanks, it was possible to estimate the duration of the spill for each type of vessel used in the study. This information is presented in Table 2.