A Tower Controller reported unidentified drones were observed in the MDT airspace; resulting in altered arrival and departure routes.

Narrative

I came to the tower to start my shift and relieve the controller that was working. He informed me that there were unauthorized drones around the airport and an airport operations vehicle was on the taxiway helping to locate and inform us of their positions. He stated he had previously had to have an aircraft depart from the opposite direction of the runway in use due to the proximity of the drones. The drones were mostly west and south of the runway; which would be the departure end of Runway 31. They were visible because they had green and red lights and some white lights; though they all seemed slightly different. The drone activity continued for about an hour while I was on position before they went away. While on the approach the pilot sounded rightfully concerned and it seemed that he was possibly considering not landing. I informed him that we had not seen any drones near the approach end of the runway and this was corroborated by the operations vehicle. The flight landed without incident and a few more flights landed after that as well. Later we had a law enforcement helicopter attempting to locate the drones between MDT and ZZZ with no real resolution. This scenario seemed to match recent news stories about drones. Other than informing the aircraft and having them depart in the opposite direction; there was nothing I or the previous controllers could do to mitigate the safety hazard the drones caused. There needs to be better mitigation and counter UAS procedures so that this cannot happen. The drones pose a significant risk to aircraft and there is no way to know who is doing this or why. This incident and related ones need to be investigated to stop it from happening again.