An air ambulance pilot reported they were on final approach to an airport without contacting the temporary Control Tower when they observed an aircraft taking the runway for departure.

Narrative

ZZZ has set up a temporary Control Tower for the next couple weeks. I knew this; but after a busy and discombobulating morning; I forgot about it as I was approaching ZZZ. I entered into a VFR traffic pattern making all the normal callouts on CTAF frequency instead of the new discrete Tower frequency. Nobody answered me; but that's not uncommon in ZZZ. When I turned final; I noticed a plane on the ground taking the runway; so I went around and steered off to the right. About that time; Tower reached out to me on CTAF to let me know of my error. I switched to their frequency and was cleared to land.Contributing factors: upon arriving at work; the phone was already ringing before I got clocked in. We were toned out for a strange request; from ZZZ1 to ZZZ2. While we were figuring out what to make of it (illegal request for us for certification reasons) the request was canceled for 'data entry error.' We were immediately toned out for another flight which had been declined by 5 other programs; including ours. The weather looked good; but we still had to comply with a meeting. So we did the meeting; but all three were anxious about getting moving on this flight that had been waiting already for hours and hours. After we came back in service; there was a sense of urgency as I still had all of my pre-flight stuff to perform; and the crew still had to make a run to the hospital for blood. When they got back; we took off for a VFR flight; which was to be flown at 17;500 to keep us above all the fire TFRs in our area. Approaching the destination; we were called on the satellite phone and told that they had failed to find any ground transportation for us at ZZZ. They asked if we could transfer the patient onto the helicopter; but we have no equipment to do that. Also; the only reason we were on the flight was that the patient was too large for the helicopter. They said OK; they'll figure something out.After landing in ZZZ3 we were notified that the ambulance had been on its way to meet us with the patient; but that they had called it and sent it back to the hospital. There were no ambulances available in ZZZ; so they were going to have another crew drive there from ZZZ4 to meet us. Our patient was going to wait in the hospital until the other crew had time to get into position.The plane was already scorching hot; and the FBO was closed; so all three of us ended up lying down on the tarmac underneath the wings of Aircraft X for a little over an hour. After we finally got the patient; we took off for ZZZ. I had intended on flying over the TFRs again; but there was a cloud layer at my intended altitude. Instead; I flew lower; but vectored to the southeast to keep clear of the TFRs. It was during this that I just forgot about the temporary Tower in ZZZ. Upon reaching ZZZ; I just conducted business as usual; attempting to communicate on CTAF.Suggestions: Be less distracted; and rely less on familiarity with potentially changing environment.