The explanation for this situation is that during the summer we spend more time outdoors and the hair accelerates its hair cycle. The end of the summer season coincides with the end of the hair cycle, which translates into a greater hair loss.
On a physical level, the changes of season can cause the appearance of small disorders in our body that we can interpret as warning signs of nature. The body instinctively prepares for the cycle change, which is not a cause for concern as long as these physical variations are within normal parameters.