It's a projection. A lot of projections have the numbers high. They're based on the numbers in other countries, mathematics, computer simulations, etc.
The projections are made so that the government and people can try to prepare for these things to happen and try to get as accurate a read as possible. Sure, sometimes it's a range that's given, but you can still estimate.
Otherwise, what are we to do? Just throw our hands up, say that no one can possibly predict anything, and have no expectations or plans?