Itaipú Dam Reservoir Changing Microclimates in Brazil

Zachary Hurwitz
Friday, August 24, 2012

When one thinks of the climate impacts of large dams in the tropics, the first thought is usually of greenhouse gases produced by rotting vegetation in a dam's reservoir and released at a reservoir's surface and a dam's turbines and spillway. But evidence is accumulating that large dam reservoirs do more than emit greenhouse gases: they are also capable of changing a region's microclimate in ecologically and economically devastating ways.

Take for example the huge reservoir of Itaipú Dam, which produces hydropower for Brazil and Paraguay. At 170 kilometers long and 12 kilometers wide, it is one of the world’s largest reservoirs, with a capacity to store 29 billion cubic meters of water. According to a class-action lawsuit filed by a thousand of the region's farmers against dam operator Itaipú Binacional, a temperature increase of 4°C has been recorded on the lands surrounding the reservoir.

The farmers claim that the temperature increase has exacerbated plant stress, causing a 30% decrease in soy production since 1984, the year the reservoir was filled. They say the hotter temperatures have also decreased animal fertility, and decreased the value of the farmers' lands, many of which directly border the reservoir.

The hot tub effect

Building a large dam reservoir is like creating a huge, solar hot tub: water stores solar radiation better than land, absorbing and trapping the sun's energy. Eventually, evaporation releases this as hot moisture into the air, increasing the overall heat and precipitation balance. In short, water's low albido – its index of solar reflectivity – can turn large reservoirs in hot climates into huge steam furnaces that can pump heat and moisture into the atmosphere.

The Brazilian government knows that climate change is transforming the country's agricultural production. A 2008 study of the Brazilian Agricultural Research Corporation EMBRAPA (“Aquecimento Global e a nova Geografia da Produção Agrícola no Brasil”) estimates that as a result of climate change, large areas of soy planted in the country's southeast are likely to be replaced by crops that perform better in hotter, wetter conditions, such as sugarcane, cassava, and coffee. However, the government has yet to admit that large reservoirs are playing a role in exacerbating regional climate change.

Instead, Itaipú Binacional has tried to sweep the phenomenon under the rug. The company has attempted to intimidate the farmers into dropping the lawsuit, which was first filed in 2003, by telling them that they would receive no compensation, while pressuring the government to throw out the case.  Prosecutors have been successful in maintaining that the case falls within the government's 20-year statute of limitations. Yet, if the lawsuit is settled rather than litigated, the Brazilian government would seek to impose a gag order, restraining publication of all documents and studies that provide evidence of the microclimatic phenomena caused by Itaipú.