What must be communicated to an aircraft if a runway has been temporarily shortened, prior to issuing a clearance?

When a runway has been temporarily shortened, it is essential to communicate the new runway number to the aircraft before issuing a clearance. This is because the runway number indicates its orientation and allows pilots to navigate to the correct runway for takeoff or landing. If the runway has been shortened, the physical characteristics of the runway may change, impacting the approach and takeoff decisions made by pilots. Therefore, informing them of the new runway number ensures they are aware of the correct runway configuration and can adjust their plans accordingly.

The other options, while important in various contexts, do not specifically address the immediate need for pilots to know which runway they should use in light of the change. The length of the new runway is significant, but it is typically included in the information associated with the new runway number, making the number itself the most critical piece of information.