The scope of requirements changes in Waterfall model is less than that in Spiral Model. In Waterfall model, you progress to the next stage only when the requirements of the stage above it are finalized and signed off. So literally, we do not have any scope of changing the requirements once we move down the phases in this model.
However, Spiral model gives us flexibility to change the requirements and scope anytime during the life cycle.
In this model, we implement the individual requirements following all the standard phases of Software Life Cycle. Therefore, if any new change is there, we can implement it in next version of the software.