"They can't rely 100% precisely because hydro is unreliable." True in an absolute sense but in comparison to solar and wind hydro is extremely reliable, and can be used to power the grid when all other energy sources fail [1,2]

As far as Mosul I'm unsure, maybe someone else more informed can chime in on the actual state of affairs there since wikipedia/google turned up multiple contradicting results for me.

[1] https://en.wikipedia.org/wiki/Hydroelectricity#Advantages

[2] http://www.hydro.org/why-hydro/reliable/