Diversification is always important, and sorry but putting all your eggs into one basket (here, hydro power) is just plain bad.

Even nuclear is not a solution, just look at France and Switzerland who had to take down a lot of their nuclear capacity beyond the broken-down NPPs because they lacked cooling water.

A decent renewable power grid has to have a lot of different energy generation paths: hydro, solar, wind, bio-gas, tidal (where possible), geothermal, enough interconnection paths to other regions, storage (battery, pumped hydro, flywheel) and regularly tested backups. The backups may even be fossil, no one has a major issue with that, the key thing is that the backup capacity must never be assumed as a regular operational capacity. And obviously, the generation capacity has to be scaled in a way that assumes a decent set of overproduction as no kind of power generation has an availabilty/capacity factor of 1... if your total consumption is, say, 100 GW, you have to have at least 200-300 GW in generation capacity.