For those fortunate enough to live in developed Western societies where access to power is taken for granted, the idea that something as prosaic as a lack of rain could result in blackouts is unthinkable.

Yet in countries like Venezuela that rely almost solely on hydroelectric power the equation is simple: no water = no electricity.

Having suffered hyperinflation and recession, the beleaguered Venezuelan population was to endure further deprivation in March as electricity rationing was enforced in six western states.

Some residents in the state of San Cristobal reported 14-hour stretches without power after a drought reduced water levels in key reservoirs needed to run the generators in hydroelectric power plants.

The crisis is not without precedent. In 2016, water levels behind Guri Dam, which provides half the country’s electricity, hit record lows and the work week was curtailed to prevent rolling blackouts.

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Nor is the problem limited to the developing world. The five-year drought in California from 2012 to 2016 led to a severe drop in hydropower generation as rivers dried up.

According to a report by non-profit organisation Pacific Institute, the cost to consumers was estimated at $2.5bn, while greenhouse gases from the power sector increased by around 10% as Californians burned more natural gas, an expensive pollutant, to make up for the lost hydropower.

The impact of climate change on hydropower

Higher temperatures as a result of climate change also mean more evaporation from the surface of reservoirs, casting further doubt on hydropower’s future as a reliable, cost-effective energy source.

Could hydro eventually be made redundant by the very climatic changes it is intended to prevent?

“Climate changes will have – and are already having – severe impacts on the entire hydrologic cycle of precipitation, runoff and evaporation,” says Dr Peter Gleick, co-founder of the Pacific Institute.

“This, of course, is closely connected to hydropower, and as we see more and more changes in water availability and river flow, we will see more impacts on hydropower.

For decades, hydropower has been seen as a cheap, flexible alternative to fossil fuels. And it remains the largest source of renewable electricity generation – producing around 17% of the world’s electricity from more than 1,200GW of installed capacity – and is predicted to remain so to 2022.

However, there are multiple drawbacks to large-scale hydro dam construction, as Gleick points out.

“Hydropower dams cause damage to free-flowing rivers and aquatic ecosystems and often, for very large dams, to communities that are displaced by construction and the creation of reservoirs,” he says. Three Gorges Dam was the worst offender in this case, displacing nearly two million people and causing severe ecological damage on the Yangtze River.

“There are fewer and fewer good places to build environmentally and economically and socially acceptable large hydro facilities, though some options certainly do still exist and could be pursued.”

Wind, sun, water: the importance of energy diversity

According to environmental group International Rivers, 14 of the 17 poorest countries rely primarily on hydropower for electricity. Reducing that reliance in favour of a diverse energy mix is a plausible solution, but, as Gleick confirms, simply building more hydropower plants is not the answer in itself.

“All energy systems benefit from diversification and infrastructure improvements, no matter where we are,” he says. “An energy system that relies on a single energy source or type will always be more vulnerable to disruption and less flexible to changing demands.

“There are places where more dams and power plants will help – but there is no single answer to the problem of drought. A diversified energy system can help reduce the negative effects of drought on hydropower, but just building more dams won’t be enough if water is not available.”

Gleick believes hydropower has an important role to play by providing storage, load following capability, and other benefits such as flood and drought protection, water supply and recreation – but like any energy system, it works best when it is integrated into a diversified and sophisticated portfolio.

“The transition to a low-carbon future is being helped by reductions in the cost of other renewables, especially solar and wind,” he says. “The fastest and easiest way to meet carbon reduction targets now is building solar and wind, which are now far cheaper and far less environmentally disruptive.”

Environmental impact and cost of hydropower

As the recent crisis in Venezuela illustrates, power shortages caused by drought resonate far beyond domestic blackouts, instead contributing to widespread economic hardship and political instability.

In the worst-hit cities, business all but ground to a halt. Reuters reports that in the western Andean state of Merida, which is serviced by the Fabricio Ojeda dam, only 150MW of power was being generated out of a possible 1,100MW.

In 2016 in neighbouring Colombia, which relies on hydropower for 70% of its power, drought-related energy shortages forced the country’s then Mines Minister, Tomas Gonzalez, to resign from his position.

According to an April 2017 report by Oxfam on the impacts of climate change in Africa, the drought in East Africa over the past three years is part of a three-decade trend. Seven of the past ten years have seen chronic droughts in East Africa due to poor or failed rains, and temperatures are rising.

Writing in ESI Africa, Tusekile Kibonde of the Africa Trade Insurance Agency (ATI) notes that the average hydropower project takes two to ten years to develop and six to 48 months to construct.

She argues that hydro can be harnessed more effectively by smaller-scale projects rather than by major ones, such as the $80bn Grand Inga project in the Democratic Republic of Congo, which, with a cumulative output capacity of 42,000MW, could conceivably power sub-Saharan Africa all by itself.

So, with water shortages as a result of global warming on the increase, and hydro development and construction costs sizeable, what role will hydropower play in a future characterised by energy diversity?

“Without a doubt there are rapid changes underway in the global energy mix as countries start to get serious about reducing greenhouse gas emissions and cutting fossil fuel use,” states Gleick.

“If we are going to build more hydro, we must be far more sensitive today to the negative impacts such facilities cause on natural ecosystems and local communities than we have been in the past.”