Hydropower is by far the most established form of renewable energy. Though not without environmental impact, either in terms of the local environment or, in the case of large dams, in terms of carbon emissions from the reservoirs behind the dams, hydro is here to stay.
Unfortunately hydropower will be affected to a far greater degree than any other renewable energy source by climate change. As the world warms, different places will see more or less rainfall, greater seasonal variability in water flow, greater then lower runoff from glaciers. It all means that though once a sure, predictable form of energy, hydropower faces challenges ahead.
Before we take a look at those though, let’s take a quick look at how much hydropower is deployed today, as well as the different types of hydropower–in terms of environmental impact all hydropower is not created equal, for sure.
As of 2011, hydropower generates 16% of the world’s electricity, some 3.5 billion kilowatt-hours annually—though in some nations, and some US states, hydropower generates nearly all of the electricity used in the region. Over the past four decades hydro has grown at a rate of about 3% annually, with over 45,000 large dams built in more than 160 nations.
That said, Brazil, Canada, China, and the United States account for over half of the world’s hydropower capacity. Paraguay, though, leads the world on a percentage basis, getting 100% of its electricity from hydro. Ethiopia gets 88% from hydro, with Venezuela getting 68%. Several other nations, either small in size, or small in installed capacity, also get nearly all their electricity from hydro: Bhutan, the Democratic Republic of Congo, Lesotho, Mozambique, Nepal, and Zambia, fall into this category.
Hydropower falls into three basic categories for electricity generation, plus one category for power storage.
The power storage part is pumped hydro. I’ve gone over this previously for Earthtechling, so I’ll just refer you there, at the previous link.
The most iconic and widespread way to generate electricity from rivers is in the form of a dam and reservoir. Not all of these are gigantic structures on the scale of China’s Three Gorges Dam, the Hoover Dam, and the like. But they all fall into that basic framework. These projects can be multi-gigawatt in capacity—perhaps why politicians love touting them, bigger being perceived as better—but also have far and away the greatest environmental impact.
Most visibly, you usually end up submerging large areas of land behind the dam. Not only is habitat, and sometimes homes, lost the reservoir fills, but as the vegetation starts decaying underwater, a good deal of greenhouse gases are released. This dissipates somewhat over time, but for a while there’s no way you can really call the electricity produced carbon-neutral, even if it’s renewable. And even later on, as the water level of the dam fluctuates seasonally, there’s always some amount of decomposition going on, on the edges of the reservoir. It’s better than fossil fuels, but not nearly as green as it may seem.
Run-of-river hydropower, sometimes called small-scale hydro, may still involve a dam being built across an entire river, but forgoes the reservoir. Instead the project relies on the flow in the river and the natural drop in elevation to generate electricity. These generally have lower environmental impact that bigger dams and reservoirs — downstream river flow is much less changed — but still can have some significant disruption to aquatic habitat. Better is that they aren’t plagued by the constant decomposition of vegetation and the resulting greenhouse gas emissions. Worse is that they are of smaller capacity.
Mini and Micro-Hydropower
Here is where hydropower gets really local–mini-hydropower referring to projects under 1,000 kW in capacity, and micro-hydropower referring to project under 100kW. Sometimes projects under 5 kW are dubbed pico-hydro, but these are very tiny indeed.
This scale of project in general disrupts the environment very little, both because of the size of any of the built components as well as the size of an reservoir that’s created. We’re talking small ponds here, not anything approaching even a lake. Most effective in places where there is no electricity grid, where any amount of electricity is a big boon, when augmented by other (hopefully renewable) power sources, hydropower at this scale could be an important niche.
Climate Change Will Boost Hydropower in Some Places, Decrease in Most
Back to the big question: How will climate change help or hinder hydropower?Recent research from Middlebury College puts this into perspective. The gist of the 80-plus page study is this:
Precipitation increases generally mean an increase in hydropower potential; temperature increases generally decrease it. Places where rivers are largely fed from glacial runoff will see a short term gain in potential, as runoff increases with warming, but face long-term declines once glaciers have largely melted. Places where weather extremes become more common see decreased predictability in output. These factors often intersect, painting a complex picture.
On a continent-wide basis, this is the scene:
In North America, parts of Canada may see hydropower potential increase as precipitation increases, though more extreme weather may muck things up; the West and Pacific Northwest of the US are expected to get hotter, with more precipitation in winter and less in summer, leading to decreased potential in summer, unfortunately when electricity demand is greater.
South America has some large regional variations, with some open questions about how climate change will affect the continent. Fortunately for Brazil, the Paraná River, where over half the nation’s hydropower is located, may see increased flow due to precipitation changes. Many places may not be so lucky.
In Europe there’s regional variability, with southern and south-eastern Europe most negatively affected. Some places could see a 25-50% drop in hydropower potential by 2070, especially Spain, Portugal, Ukraine and Bulgaria. That said, some places may seem short-term increases in hydropower potential, due to short-term increases in glacial runoff—think Switzerland, where roughly 40% of the electricity comes from hydropower.
The Middle East is nearly uniformly badly hit by climate change, with temperatures increasing and precipitation decreasing. Turkey could see particularly sharp declines in hydropower potential.
Africa has large variations, not surprising considering we’re talking about a gigantic area. On average though climate change could bring about a 10-20% decrease in rainfall, which could have an outsized impact considering how large a role hydropower plays in some nations’ energy mix. Conversely though, in terms of human impact, the already sporadic availability of electricity in many places means that, ironically, this may not have as much of a practical difference in the day to day lives of people as it would in places where the electricity supply is more reliable today.
Some potentially devastating consequences await though. This amount of declining rainfall could mean some rivers in places as far apart as Botswana and Tunisia dry up completely. An entire swath of land from Senegal to Sudan is at great risk from changes in water availability, due to increasing temperatures and decreasing precipitation. For those not up on geography, Ethiopia, nearly entirely dependent on hydropower, with some controversial large projects in the works, is in this region.
Asia, with over nearly one-third of the world’s population, rapidly rising to reclaim its historic place atop all human civilization, as well as having a large amount of hydropower, is likely to face gargantuan challenges.
A couple issues stick out: Unpredictability in precipitation, combined with extreme weather is likely to increase, bringing drought and flooding. Two of the main rivers of South Asia, the Indus and the Ganges get about 40% their water from glacial runoff, with glaciers in the region on the whole in pretty rapid retreat. This means increased capacity (and potential flooding) in the short-term, followed by much reduced capacity in the future. Some rivers could dry up completely—a repeat of events from nearly four millennia ago when the Saraswati River dried up due to climatic changes, forcing the mass migration of early civilization in the region to the east. This time there is nowhere to go.