A lot of people, including me, think the exact opposite: we should be tearing down as many existing dams as possible. Dams are extremely damaging to river ecosystems and are a huge contributor to coastline erosion and exacerbate droughts.

http://news.nationalgeographic.com/2016/11/dam-removal-nelso...

One has of course to learn from the mistakes of the past when deciding where and how to plan and manage dams. But California seems to suffer alternating from floods after the snow melt and droughts in between. The current dam infrastructure is to buffer the floods and release the water at a more constant rate through the season. I cannot see how this could create droughts.

Here in Germany we traditionally have more water than we need, but recently the weather is more extreme. We get stronger rains in shorter times, leading to flooding and times with less than usual water. More dam capacity is the obvious solution to that.

Preferably, dams should not be built in the middle of a living river system, but higher up in the mountains, capturing the seasonal water. Also, where needed, small bypass rivers should be kept, allowing fish to migrate freely.

Dams contribute to droughts by limiting the recharge of downstream ground water levels and aquifiers.

Can you explain why? Over the year they would release the same water as the river without the dam would do - just not in a peak flood but reduced to a constant flood rate.

Dammed rivers release less water because of increased evaporation. Another problem is riverbed deepening which lowers the groundwater table. Where the water pools up is also important - having a bunch behind a dam when former wetlands and floodplains are dry is obviously not conducive to the ecosystems in those wetlands and floodplains.

Doesn't that all very heavily depend on the exact nature of the system the dam is part of? We all know of the environmental problems of the Assuan dam in Egypt. But that does not mean that properly planned dam cannot be very beneficial. One shouldn't just build a dam where it is convenient but with careful analysis first. There are plenty of places where a dam just means less cities flooded occasionally but otherwise has little eco system impact.

Why do dams increase evaporation? Having the water all in one place as opposed to distributed over the length of a river should reduce surface area.