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Recent research has quantified the cumulative impact of dams on Brazil’s native savanna ecosystem, the Cerrado. The study created an index of the direct and indirect impacts of constructing hydroelectric facilities on both the rivers being dammed and the surrounding ecosystem.

While often offered as a cleaner alternative to fossil fuels, dams can have severe environmental impacts ranging from deforestation to obstruction of fish migrations, water pollution, and even direct greenhouse gas emissions resulting from inundation of the surrounding area. This study assessed these effects cumulatively, weighting them more heavily if multiple dams were present in a single watershed.

“For freshwater systems, there’s not the equivalent of a deforestation rate. We don’t have an easy metric of ecosystem damage. So this study was one way of building a method for assessing the unintended consequences of installing a dam in a Cerrado watershed,” says Woodwell Water program director Dr. Marcia Macedo, who collaborated on the paper.

The study puts forward a new Dam Saturation Index (DSI) for the region to approximate the environmental impacts of existing dams. High-saturation watersheds were concentrated in the central and western portions of the biome, and most planned dams are located in sensitive areas of native vegetation with little protection.

Understanding hydropower in Brazil

Hydropower is big in Brazil—66% of the country gets some or all of their energy from it. Harnessing the power of a river is often the easiest means of electricity production in rural and remote areas. However, large hydroelectric plants are more often used as a means of infrastructural support for extractive industries like mining, rather than to expand access to electricity for rural citizens. Conflicts have already arisen between communities and hydroelectric plants.

Conflict over water usage in the Cerrado is expected to increase as the region continues to get hotter and dryer due to human-caused climate change. Land use change in the biome has accelerated the impacts of climate change, removing the cooling and moisture-retaining effects of natural vegetation.

“There are a lot of dams already, and many more planned, and it’s only going to get more contentious as climate change continues,” Dr. Macedo says. “In the northern and eastern part of the Cerrado, it’s already quite dry. We’re already seeing conflict over water and these reservoirs could just make that worse as upstream locations are able to withhold water from those downstream.”

What this means for the Cerrado

The Cerrado has historically not garnered as much attention, or as many demands for its protection, as the neighboring Amazon rainforest. Less than 10% of the Cerrado is considered protected, and many of those protections are biased toward terrestrial habitats and species. Lack of research into the full impact of hydropower on the watersheds of the Cerrado has left the region vulnerable to unchecked development. Some dams have even been built in areas otherwise strictly protected. Dr. Macedo hopes this study will encourage a different attitude towards freshwater resources.

“There is a question of how we can innovate thinking about protecting freshwater systems, especially under climate change. They’re so important, and there are so many resources—fisheries and clean water and more—that come from these systems,” Dr. Macedo says.

This study focused on large hydroelectric dams, but Dr. Macedo notes that there are many more small dams, built to serve individual farms, that also impact the flow of headwater streams. Ongoing research is focused on understanding the cumulative impacts of dams of all sizes on tropical watersheds.

As the planet warms, drought is an increasing threat in many regions. Research led by Woodwell Research Assistant Isabelle Runde, modeled the frequency of drought across the globe, analyzing drought changes in forest, food, and energy systems as temperatures surpass 2, 3, and 4 degrees Celsius.
Models show that unlike in a stable climate, unreliable water resources and increasing temperatures make drought more likely in many places. For every increase of 0.5 degrees C, an additional 619 million people could become exposed to extreme drought 1 in every 4 years. This is in addition to the 1.7 billion people (nearly a quarter of today’s global population) who are already exposed to these conditions in a world that has warmed by a little more than 1 degree C.

2 Degrees of Warming Risks Damaging our Best Forest Carbon Sinks

Tropical forests are one of the planet’s key natural climate solutions— able to prevent 1 degree of warming through both carbon sequestration and regional cooling effects. Deforestation, fragmentation and degradation from things like fire, and disease threaten to turn these forests from a vital sink to a source of emissions.

In recent years, the Amazon has been a net carbon source due to increased extreme drought and deforestation, leaving the Congo rainforest as the world’s last remaining stable tropical forest carbon sink.

As warming surpasses 2 degrees, the annual likelihood of drought in the Congo rainforest begins increasing faster than in the Amazon. Drought can make a forest more susceptible to further degradation, such as fire or disease, and reduces carbon sink capacity by stressing or killing trees and placing the ecosystem under stress.

Productivity is Threatened in the Breadbaskets of Mediterranean, Mexico, China

Global crop production is highly concentrated in key breadbasket regions— nearly 72% of the world’s maize, wheat, rice, and soy are produced in just 5 countries. Extreme drought can reduce the productivity levels of these staple crops, among others, potentially triggering widespread food insecurity, hunger and economic disruption.

By 2 degrees of warming, the probability of drought in the breadbasket regions of both China and the United States will be greater than 50% — meaning an extreme drought roughly every other year.

Disruption will be much higher in countries where jobs in agriculture comprise a large segment of the economy. In Mexico, one of the world’s top 10 producers of maize, 12% of the workforce is in agriculture and at 1 degree, the country already has among the greatest areas of cropland exposed to drought. 90% probabilities—indicating near-annual drought—begin to emerge in some parts of the country at 2 degrees of warming.This kind of recurrent extreme drought will stress water resources for agriculture.

The Mediterranean also is a drought hotspot. Drought probability in Mediterranean croplands will increase rapidly between 2 and 3 degrees of warming, rising from just 10% to over 50% of cropland affected by drought in 3 out of 4 years.

Drying Rivers Will Plunge Hydro-dependent Countries into Energy-Shortages

Hydroelectricity supplies a sixth of global energy demand, and is a low-cost, low-emission alternative to fossil fuels. The overwhelming majority of new hydropower plants since 1990 have been constructed in fast-growing, developing nations.

High dependence on hydropower makes countries like Brazil and China vulnerable to energy disruption during periods of drought. Brazil draws nearly two thirds of its energy from hydroelectric resources. During a three year drought between 2012 and 2015 in Brazil, hydroelectric generation declined by 20% each year. If warming exceeds 3 degrees C, more than half of Brazil’s hydroelectric capacity will experience a likelihood of annual drought greater than 50%.

Extreme drought can also be counterproductive to reducing carbon emissions. During years of drought, expensive fossil fuel based energy is often brought in to fill demands. In addition, droughts often coincide with extreme heat events, when electricity demand peaks to run air conditioners. Beyond 3 degrees of warming, more than a third of the planet’s hydroelectric capacity will likely be exposed to extreme drought every other year.

Projections of a Dryer World

Current international climate goals aim to limit warming to between 1.5 and 2 degrees C, but without urgent intervention, we are on track to push past that limit to at least 2.5 degrees C. Projections past 2 degrees of warming show a future where extreme drought is common, exposing already-vulnerable people, places, and economies to greater water shortages, while making it even harder to curb emissions. In order to guard water resources and the systems that depend on them, emissions need to be cut rapidly. And places already feeling the impacts of warming will need to brace to adapt to a hotter, dryer version of the world.

Recent study shows widespread patterns of loss, upending scientists’ previous projections

The Arctic is no stranger to loss. As the region warms nearly four times faster than the rest of the world, glaciers collapse, wildlife suffers and habitats continue to disappear at a record pace.

Now, a new threat has become apparent: Arctic lakes are drying up, according to new research published in the journal Nature Climate Change. The study, led by University of Florida postdoctoral researcher Dr. Elizabeth Webb in collaboration with Woodwell Associate scientist, Dr. Anna Liljedahl, flashes a new warning light on the global climate dashboard.

Research reveals that over the past 20 years, Arctic lakes have shrunk or dried completely across the pan-Arctic, a region spanning the northern parts of Canada, Russia, Greenland, Scandinavia and Alaska. The findings offer clues about why the mass drying is happening and how the loss can be slowed.

The lake decline comes as a surprise. Scientists had predicted that climate change would initially expand lakes across the tundra, due to land surface changes resulting from melting ground ice, with eventual drying in the mid-21st or 22nd century. Instead, it appears that thawing permafrost, the frozen soil that blankets the Arctic, may drain lakes and outweigh this expansion effect, says Dr. Webb. The team theorized that thawing permafrost may decrease lake area by creating drainage channels and increasing soil erosion into the lakes.

These lakes are cornerstones of the Arctic ecosystem. They provide a critical source of fresh water for local Indigenous communities and industries. Threatened and endangered species, including migratory birds and aquatic creatures, also rely on the lake habitats for survival.

“Our findings suggest that permafrost thaw is occurring even faster than we as a community had anticipated,” Dr. Webb said. “It also indicates that the region is likely on a trajectory toward more landscape-scale drainage in the future.”

If accelerated permafrost thaw is to blame, that’s unwelcome news. The Arctic permafrost is a natural warehouse of preserved organic matter and planet-warming gasses.

“Permafrost soils store nearly two times as much carbon as the atmosphere,” Dr. Webb said. “There’s a lot of ongoing research suggesting that as permafrost thaws, this carbon is vulnerable to being released to the atmosphere in the form of methane and carbon dioxide.”

According to Dr. Liljedahl, this study shifts the perspective on prior research—there is still more to learn when it comes to how climate change is altering the Arctic landscape.

“This work shows that we are “living the future” already,” said Dr. Liljedahl. “Or if you look at it from the other perspective, the current models used to project future surface water coverage and permafrost thaw across the Arctic are “off”. They are not capturing key processes. We have already seen reduced lake coverage happening over the previous two decades.”

There is a silver lining in the researcher’s findings. Previous models of lake dynamics predicted lake expansion, which thaws the surrounding permafrost. But because lakes are drying, near-lake permafrost is likely not thawing as fast.

“It’s not immediately clear exactly what the trade-offs are, but we do know that lake expansion causes carbon losses orders of magnitude higher than occurs in surrounding regions,” Dr. Webb said. “So it should mean that we won’t see quite as much carbon emitted as previously thought, because lakes are drying and not wetting.”

The research team used a machine-learning approach to examine the climate change mechanisms responsible for lake area change. By harnessing large ensembles of satellite images to assess patterns of surface water loss, they were able to analyze decades of data across the Arctic. The data is available on the Permafrost Discovery Gateway (PDG), a project that Dr. Liljedahl leads, the goal of which is to make permafrost data broadly accessible to encourage Arctic change research.

“We made the pan-Arctic dataset, including both long-term trend analysis and individual years, accessible on the PDG so that anyone with internet access can interact with the dataset. We are still building the PDG visualization and analysis tools so more options to enable discovery will become available in the coming two years,” said Dr. Liljedahl

The best way to curtail the lakes’ demise and protect permafrost is to
cut fossil fuel emissions and limit global temperature rise.

“The snowball is already rolling,” Webb said, stating that we need to act now to slow these changes. “It’s not going to work to keep on doing what we’re doing.”