I’m happy to be wrong about this globally, but in my neck of the woods the readily exploited hydro resources are already exploited to 90% of their capacity and have been for 100 years. Hydro is in many ways the ultimate renewable energy, but that’s been true since electrification and we’ve been using it as part of the energy mix since then. I’d love to be wrong but my understanding is that there isn’t a huge amount of untapped new hydro capacity available without having severe impacts on ecosystems

This is even more true with international grid connections. Europe in a cold spell? Solar countries import, wind & hydro export. Europe in a heat wave? Flip the switches the opposite direction.

Hydroelectric capacity is largely built out, so you can look at current generation mix to see how much it is likely to contribute.

In the US capacity is likely to go down (dams are expensive and many time old dams are removed instead of being rebuilt).