I would say this is a yellow " flava ". Although it resembles " schutschensis " and looks an interesting individual, it shows traces of yellow and green both on the supercilium and scapulars .First winter Eastern yellow wagtail " schutschensis " typically has completely grey and white plumage and might have very restricted yellow on vent . In both cases, it would be very difficult to make sure unless there is a sound recording . Did you hear it call ??