Quite a few users I work with update both the project description and task descriptions as they work through a project - this is helpful for them to track unexpected changes in scope or summarize new information. However, there is no way to @ someone or create a notification when the description is changed. Even if they are @ within the description, a notification is not sent which creates a breakdown in communication.
Hi @Kay_Watt , welcome to the forum 
I believe that the task description was designed to be set at the start of a task and not frequently updated. In your case, to keep your workflow intact, the simplest way would be everytime someone changes the description to simply add a comment to the task 'see updated description ’ or something along those lines…
That way, all collaborators will get the update in their Inbox, while in the activity log (chat history) everyone will clearly see all the times that the description (or scope in your case) was updated.
As for updates to the project description, you can use the Messages tab to inform the same to all Project members (that have notifications on for Messages), or better yet use the project’s Status Update feature.
Hope this helps! 