How can I judge whether a department has a welcoming atmosphere for women students?

Do not rely only on a department’s official description. At an open day or information session, ask current students and faculty specifically about classes, laboratories, student interactions, consultation routes, harassment prevention, and support related to health or family responsibilities. Observe classes or facilities when possible, including how staff respond to questions and how students treat one another. Rather than judging from the number of women students alone, check through several sources whether students can speak comfortably and can obtain help when problems arise.