Research by MapBiomas indicates that land use dynamics based on the conversion of forests to livestock and agriculture, as well as the construction of dams, contribute to the decrease in water flow

Where did the water go?" This was a recurring question that MapBiomas scientists asked themselves after analyzing satellite images of the entire national territory between 1985 and 2020. The data, which are available here, indicate a clear trend of surface water loss in all hydrographic regions and biomes across the country.  

In total, the reduction in water-covered surface in Brazil has been 15.7% since the early 1990s, decreasing from almost 20 million hectares to 16.6 million hectares in 2020. Although this area is equivalent to the state of Acre or nearly 4 times the size of the state of Rio de Janeiro, since 1991, when it reached 19.7 million hectares, there has been a 15.7% reduction in water surface in the country. The loss of 3.1 million hectares over 30 years is equivalent to one and a half times the water surface area of the entire Northeast region in 2020. 

MapBiomas Water coordinator, Carlos Souza Jr., comments that the result is quite concerning because the signal of the water reduction trend in Brazil, using satellite data, is very clear. "Evidence from the field already indicates that people have begun to feel the negative impact with the increase in wildfires, impact on food production, energy production, and even with water rationing in large urban centers," he warns.

According to the researcher, there are several factors that can explain the reduction in water surface area in Brazil over the past 36 years. "The land use dynamics based on the conversion of forests to livestock and agriculture interfere with the increase in local temperature and often alter river and spring heads, which can also lead to river and lake siltation. The construction of dams on farms for irrigation, watering along rivers reduces water flow; and, on a larger scale, large dams for energy production, with extensive water surfaces subject to evapotranspiration processes that lead to water loss to the atmosphere," he says. 

The state with the highest absolute and proportional loss of water surface in the historical series analyzed by the MapBiomas team was Mato Grosso do Sul, with a reduction of 57%. In 1985, the state had over 1.3 million hectares covered by water, but by 2020 there were only slightly over 589,000 hectares. This reduction occurred mainly in the Pantanal, but the entire Paraguay basin lost water surface. In second place is Mato Grosso, with a loss of almost 530,000 hectares, followed by Minas Gerais, with a negative balance, between the water that entered and that drained, of more than 118,000 hectares.

The Pampa, despite being the smallest Brazilian biome, has the third largest area of water surface, mainly due to the presence of large coastal lagoons, such as the Lagoa dos Patos, Lagoa Mangueira, and Lagoa Mirim. The Lagoa dos Patos accounts for around 56% of the water surface in the biome, and the three lagoons together represent more than 81% of the total water surface. 

In the Pampa region, there is a high density of artificial reservoirs used for irrigating rice cultivation, most of which were constructed before 1985. During the period analyzed by the platform, there was a continuation in the creation of new reservoirs, with emphasis on municipalities like Dom Pedrito and Uruguaiana, both in Rio Grande do Sul. 

The construction of artificial reservoirs in the Pampa region does not necessarily result in water loss in the biome, according to Juliano Schirmbeck, a professor and member of the MapBiomas Pampa and MapBiomas Water teams. "On the contrary, it tends to increase the amount of surface water present. The potential negative impacts of these reservoirs are associated with alterations of natural drainage networks, reducing the quantity of water and its characteristic variations over time in small streams, with undesirable consequences for biodiversity and ecosystem services," he explains.  

Among the biomes, the Pampa is the one showing the least tendency of water surface reduction, accounting for just over 1% of the total water area in the biome. "In absolute terms, part of the losses observed in the period were compensated by the increase in the number of reservoirs. In relative terms, this trend tends to be less significant also due to the presence of the large mass of water in the coastal lagoons," comments the researcher.  

In general, the loss of natural water surface due to water stored in structures built by humans has concerning consequences on the alteration of the water regime, affecting biodiversity and river dynamics. The Pantanal is one such example, with the construction of hydroelectric dams on the rivers that form the biome. However, there are dozens of other dams planned for this region, with little contribution to the power system and a great potential for impacts. 

However, it is still possible to reverse these processes with water resource policies and management. "The first step is to diagnose the problem at the watershed scale to identify which factors are compromising the availability of water resources. Second, it is possible to develop a multisectoral action plan to mitigate and even reverse the problem. But, we must not forget that a large part of the solution will depend on reducing greenhouse gas emissions to control the increase in global temperature," adds the coordinator of MapBiomas Água. 

Where is the water in Brazil 

Brazil has 12% of the planet's freshwater reserves, constituting 53% of South America's water resources. There are 83 border and transboundary rivers, as well as watersheds and aquifers. Transboundary watersheds cover 60% of Brazil's territory.

 The biome with the largest area covered by water in Brazil is the Amazon, with over 10.6 million hectares of average area, followed by the Atlantic Forest (over 2.1 million hectares) and the Pampas (1.8 million hectares). The Pantanal occupies the fifth position, with just over 1 million hectares of average area, behind the Cerrado (1.4 million hectares).  

About MapBiomas Water

It is a groundbreaking initiative for mapping the dynamics of surface water and water bodies throughout the national territory since 1985. Similar to MapBiomas Fire, the Water series processed over 150,000 images generated by Landsat 5, 7, and 8 satellites from 1985 to 2021. With the help of artificial intelligence, the area covered by water was analyzed in each 30m x 30m pixel of the over 8.5 million square kilometers of Brazilian territory over the 37 years between 1985 and 2021, distinguishing natural and anthropic water bodies. In total, 108 terabytes of images were processed, revealing areas, years, and months of higher and lower water coverage. The method also allows for identifying the area with water each month throughout the period, as well as transitions and trends. 

The data can be found in maps and annual, monthly, and cumulative statistics for any period between 1985 and 2021 on the platform, open to everyone. 

See the new features on the MapBiomas Água platform presented in the webinar "Exploring the connections of surface and groundwater" below:

Access the main results of MapBiomas Água for the period from 1985 to 2020 in the Fact Sheet.

Watch the launch of MapBiomas Água: