What can this component be?
Many anemometer installations require long wiring runs, which, even for distant lightning strikes, are subject to high voltage spikes. Further, these long lengths of cable at the rated 30V DC can have inductive effects, so while the PCB doesn't include an inductive part, it could still be subject to inductive kickback which the diode will handle, preventing contact degradation.

A TVS diode in parallel with the reed switch helps protect the reed from arcs from either high voltage events, or possible inductive issues with the measuring equipment or long cable length.

While most TVS diodes optimize for low capacitance, you can get TVS diodes with enough capacitance to accommodate the bounce of a low-bounce reed relay.  With a good magnet design you can lower the bounce even further so the TVS capacitance is enough to manage the bounce altogether. It's possible this part is playing two roles.

Given that it's marked D1, this is my guess. You could put it into a curve tracer to verify, though if it is a TVS diode you'll need a high voltage curve tracer.