Methodology for oil spill vulnerability assessment: Environmental sensitivity mapping in the Gulf of Mexico

This study presents the development of an Oil Spill Physical Vulnerability Index (OSPVI_s,h) for environmental sensitivity mapping in the Mexican Exclusive Economic Zone of the Gulf of Mexico. The OSPVI_s,h was calculated using more than 28,000 independent Lagrangian numerical simulations of oil spills spanning a 26-year period (1994-2019). Continuous daily releases of 1000 bbl/day of Isthmus/Maya blend crude oil were simulated for 30 days. Using a critical impact threshold of 0.01 g/m², three key metrics were estimated: maximum hydrocarbon concentration at the surface, maximum probability of impact, and exposure time, to construct the OSPVI_s,h which has values between 0 and 1. The results indicate that Veracruz and Tabasco are vulnerable regions year-round, with OSPVI_s,h values ranging from 0.5 to 1.0, and minimum arrival times indicating coastal impacts within the first week of an incident. In Campeche, impacts are primarily offshore, with coastal areas exhibiting medium OSPVI_s,h values (>0.3 & ≤0.5). In contrast, the coastal zone of Tamaulipas is the most affected, exhibiting medium to very high OSPVI_s,h values (>0.3 and ≤1.0) due to its proximity to the oil exploitation zone. Finally, the OSPVI_s,h was integrated with geospatial data to generate Integrated Environmental Sensitivity Maps, identifying mangroves, sandy flat coasts, marine mammal habitats, and commercial fisheries (including sharks and rays) as the resources most vulnerable to oil spill impacts.