https://www.usnews.com/education/best-global-universities/spain/environment-ecology
https://www.usnews.com/education/best-global-universities/articles/subject-rankings-methodology
"These subject-specific rankings – which are not of academic majors, departments or specific schools at universities, such as business or medical schools – are based on academic research performance in those subjects. U.S. News has used various bibliometric measures, including publications and citations, as well as indicators for global and regional reputation in each specific subject."