Climate change could drastically reduce aquifer recharge in Brazil

(Press-News.org) The global climate crisis could significantly impact the natural replenishment of Brazilian aquifers, reducing the groundwater supply across the country. This is the conclusion of a study by scientists from the University of São Paulo’s Institute of Geosciences (IGc-USP) and the National Institute for Space Research (INPE). The scientists analyzed the impact of various climate scenarios on water availability by the end of the century. The study was published in the journal Environmental Monitoring and Assessment.

Groundwater is water that accumulates below the Earth’s surface in geological formations called aquifers. It slowly infiltrates the soil after rainfall and supplies wells, springs, rivers, and ecosystems. In Brazil, an estimated 112 million people (56% of the population) rely totally or partially on this source.

The IGc-USP and INPE study employed a water balance model based on geoprocessing and corrected climate projection data from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to estimate temperature, precipitation, surface runoff, and aquifer recharge changes between 2025 and 2100. CMIP6 unifies data from various research centers worldwide and is the most recent model produced by the World Climate Research Program (WCRP).

The research considered two greenhouse gas emission scenarios: one moderate and one pessimistic. “What we found was the possibility of a drastic decrease in aquifer recharge in the country, especially in the Southeast and South regions, which will become drier according to virtually all the climate models analyzed,” says Ricardo Hirata, full professor at IGc-USP and first author of the article.

The results show that the country is expected to experience consistent temperature increases throughout the century, ranging from 1.02 °C to 3.66 °C depending on the scenario and period considered. At the same time, rainfall distribution is likely to become more uneven. The North region and part of the east coast are expected to see a drop in average annual precipitation, while the South and parts of the Northeast (especially Ceará, Piauí, and Maranhão) may experience occasional increases.

“Even in regions such as the Southeast, where the total amount of rainfall isn’t expected to vary greatly, we’ll see a change in the regime, with rainier summers and longer dry periods. Very intense and concentrated rainfall promotes surface runoff and can cause flooding, but doesn’t favor water infiltration into the soil. And without infiltration, there’s no recharge,” says Hirata.

The researcher points out that, even when water penetrates the soil, it can take months to reach the aquifer. “In several of our studies, we’ve seen that it takes water two or three months to travel 10 to 15 meters through the soil and reach the water table. If the rain is too intense and lasts only a short time, that water doesn’t make it there,” he notes.

In the most affected areas, underground recharge may decrease by up to 666 millimeters per year. The most critical situation is expected to occur in the Bauru-Caiuá Aquifer System (located in Brazil’s Central-West region and spanning parts of the states of Minas Gerais, São Paulo, Goiás, Mato Grosso do Sul, and Mato Grosso), with a 27.94% reduction in recharge volume. Other important aquifers, including the outcrop areas of Guarani (in parts of the states of Minas Gerais, São Paulo, Goiás, Mato Grosso do Sul, Mato Grosso, Paraná, Santa Catarina, and Rio Grande do Sul), Furnas (Bahia, Goiás, and Minas Gerais), Serra Geral (Mato Grosso do Sul, São Paulo, Paraná, Santa Catarina, and Rio Grande do Sul), Bambuí Cárstico (Piauí, Paraíba, Pernambuco, Bahia, Goiás, and Minas Gerais), and Parecis (Rondônia, Amazonas, and Mato Grosso), are also expected to suffer significant losses (read more at revistapesquisa.fapesp.br/en/aquifer-depletion-threatens-forests-and-rivers/). 

Lack of attention to the problem

Despite its strategic importance, the underground dimension of the water crisis has received little attention from public policies. “Groundwater continues to be overlooked in the discussion about climate change. When we talk about the climate, we talk about rivers, vegetation, agriculture. But aquifers aren’t on the agenda,” Hirata points out.

He notes that more than half of Brazilian municipalities rely on groundwater for their water supply. “We have a huge water reserve that’s resilient to variations in recharge. Even in years of drought, the aquifer continues to supply water because its storage capacity is so large. This is what happened during the great drought of 2014-2016. Cities supplied by surface water were twice as affected by the water crisis as those supplied exclusively by groundwater,” says Hirata. Brazil has approximately 3 million drilled tubular wells and 2 million dug wells, which extract between 550 and 600 cubic meters of water per second. Eighty to ninety percent of this total is used for private purposes, including agriculture, industry, services, and supplemental residential supply in urban areas.

One example is the city of São Paulo. “Only 1% of the public supply comes from aquifers. But there are about 13,000 private wells in the metropolitan area that account for 11 cubic meters per second. During the water crisis, this supplied 25% of the demand,” Hirata quantifies. Despite the obvious distortion, he argues that private use plays an important social role: “It may seem contradictory, but when the rich use water from wells, there’s more water left in the network for the poor.”

Solutions

The study not only points out problems but also proposes solutions. One promising strategy is managed aquifer recharge (MAR), which uses techniques to promote the infiltration of rainwater or treated sewage. MAR includes direct injection into the aquifer, as is already the case in Madrid, Spain.

The researcher explains that managed recharge can be done with simple structures, such as infiltration basins or small dams, or with more sophisticated direct injection systems. “It’s possible to capture rainwater or even treated sewage and channel it into planned infiltration systems. The soil acts as a biogeochemical super-reactor, capable of purifying the water as it travels to the aquifer.”

In large cities such as São Paulo, some underground recharge occurs involuntarily. “Isotope studies show that about 50% of the recharge in the central region comes from leaks in the water and sewage networks. This shows that urban occupation can also positively affect underground processes,” Hirata points out.

The study was supported by FAPESP through a postdoctoral fellowship awarded to Leila Goodarzi and a direct doctoral fellowship awarded to Fernando Schuh Rörig. They are both members of the team and the Thematic Project “SACRE – Integrated Solutions for Resilient Cities”. 

In October, Hirata will receive an award from the Federal Council of Engineering and Agronomy (CONFEA) for his four decades of work in defense of groundwater. Hirata is the author, with collaborators, of “Groundwater and its Environmental and Socioeconomic Importance for Brazil”.

About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe. 

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