A new study by Ruijie Zeng and colleagues at the University of Illinois, Urbana Champaign, examines the relationship between hydropower (dams) and irrigation (mainly for food production .
Hydropower dams are often assumed to benefit agriculture, catching and regulating wild waters to bend them to human use. The researchers find that this is not always true, with some 54% of hydropower sites compete with irrigation.
“We find that 54% of global installed hydropower capacity (around 507 thousand Megawatt) competes with irrigation. “
A large factor in this “competition” is due to the need for flood control, which retains water (at the dam rather than the downstream fields) and increases evaporative loss over all.
In the global assessment, they found geographic patterns, which appear to reflect local climate. In particular, conditions that lead to higher potential evaporation “may lead to larger tradeoffs and competition for water use in those regions with warm climates, such as India, South China, and parts of the Southern U.S”.
This comprehensive study of all major hydro projects on Earth assembled data from a variety of sources.
“[T]he datasets compiled for the assessment of hydropower-irrigation relationships include hydroelectricity generation, installed hydro- power capacity, irrigation water use and climate variables.”
The data from all these sources was reorganized to reflect these variables in each of 320 “Food Producing Unit” (FPU), which are areas in a single river basin with similar climate and agricultural characteristics. The study used 93 of the FPUs that have hydropower.
This synthesized dataset was analyzed with machine learning techniques, which suggested three categories of relationship between hydropower and agriculture (roughly: negative, neutral, and positive).
This somewhat heroic effort gives a very broad view of the whole planet. (And it is just about all the data possible—approaching a 100% sample!) This data not only lets us compare projects around the world, but also eliminates artificial limits on data due to political boundaries (e.g., where a dam in one country affects irrigation in another country).
From this perspective, there were some useful findings. Hydropower isn’t always good or bad for irrigation. It depends on the climate—rainfall and evaporation—of the specific location. So, just because it worked well in California doesn’t mean it will necessarily work the same way in Mississippi.
We should keep in mind that this study only covered a few years. Things can change. Indeed, the 2005 – 2013 period covered in the study saw California enter a prolonged dry period, which was punctuated this year by a wet winter. Other areas have also had record breaking dry spells as well. I do not know what these relative extremes of rainfall would do if the study is extended.
And, of course, long term climate change likely will alter this balance in different regions.
This is nice work, and makes clear that even renewable energy sources have undesirable impacts, though it may not be a simple story.
- Ruijie Zeng, Cai Ximing, Ringler Claudia, and Zhu Tingju, Hydropower versus irrigation—an analysis of global patterns. Environmental Research Letters, 12 (3):034006, 2017. http://stacks.iop.org/1748-9326/12/i=3/a=034006