Hydropower expansion in an already transformed tropical transition basin: cumulative pressures on Indigenous Lands in the Sangue River Basin, southern Amazon, Brazil

Technical Summary: Hydropower Expansion in the Sangue River Basin

Problem Statement
Hydropower expansion is frequently promoted as a cornerstone of low-carbon energy transitions, yet its development often overlaps with tropical river basins that have already undergone extensive land-use change. While cumulative impacts of hydropower are increasingly studied, there is a significant gap in understanding the pre-existing landscape conditions under which new projects emerge. Most assessments evaluate hydropower as an isolated source of environmental change, often failing to incorporate the degree of prior anthropogenic transformation into watershed-scale analyses. This oversight raises a critical question: is contemporary hydropower expansion in tropical basins advancing into relatively conserved landscapes or into territories that have already experienced substantial land-use conversion? This issue is particularly acute where hydropower development intersects with Indigenous territories, which often serve as the last remnants of native ecosystems amidst intensifying external pressures.

Methodology
This study investigates the Sangue River Basin in the southern Amazon (Mato Grosso, Brazil), a region characterized by the coexistence of agricultural frontiers, Indigenous Lands, and a growing portfolio of hydroelectric projects. The research integrates three primary datasets within a watershed-scale framework:

1. Land-Use and Land-Cover (LULC) Dynamics: Annual maps from 1985 to 2024 were sourced from MapBiomas Collection 10. Data were reclassified into eight categories and aggregated into "Natural Cover" (Forest, Savanna, Grassland, Wetland) and "Anthropic Cover" (Agriculture, Pasture, Non-Vegetated Areas) to quantify long-term landscape transformation.
2. Hydropower Development Chronology: The timeline of hydroelectric interest was reconstructed using official records from the Brazilian National Electric Energy Agency (ANEEL), the Mato Grosso State Secretariat for the Environment (SEMA-MT), and the Official State Gazette. The chronology was established based on the earliest formal record of interest for each project, including feasibility studies, Declarations of Water Availability Reservation (DRDH), and various licensing stages (Preliminary, Installation, Operation).
3. Spatial Integration: The analysis integrated the spatial distribution of four Indigenous Lands (Japuíra, Erikpatsá, Manoki-Irántxe, and Ponte de Pedra) with the temporal trajectories of landscape change and hydropower project emergence.

Key Results

• Substantial Landscape Transformation: Between 1985 and 2024, the Sangue River Basin underwent significant conversion. Native vegetation declined from approximately 87% to 57% of the basin area, while anthropized land increased from 13% to 43%. The most rapid transformation occurred between the mid-1990s and early 2000s, driven by agricultural expansion.
• Temporal Disjunction: The chronology of hydropower interest reveals that the first formal records (primarily Small Hydropower Plants, or PCHs) appeared in the early 2000s. This coincided with a period when the basin had already undergone substantial land-use conversion. Interest in larger Hydroelectric Generating Centers (CGHs) emerged later, with a concentration of proposals between 2020 and 2022, well after anthropized land cover had become firmly established across much of the watershed.
• Superimposition of Pressures: The study finds that current hydroelectric expansion is superimposed on an already anthropized watershed rather than initiating land conversion. The coexistence of multiple hydropower projects (including operating, licensed, and proposed facilities) with four Indigenous Lands highlights the accumulation of socio-environmental pressures. While Indigenous Lands retain extensive native vegetation, they are increasingly surrounded by transformed landscapes, particularly near the Manoki Indigenous Land.

Key Contributions
The paper contributes to the field by shifting the analytical focus from individual project assessments to a basin-scale perspective that integrates historical land-use dynamics. It demonstrates that:

• Hydropower expansion in the Sangue River Basin is not the primary driver of landscape transformation but represents a new layer of pressure added to a pre-existing altered context.
• Evaluating hydropower projects individually underestimates their territorial implications, as it fails to account for the cumulative effects of decades of agricultural expansion and infrastructure development.
• The interaction between energy development and Indigenous territories in already transformed landscapes creates a complex scenario of cumulative socio-environmental risks that conventional, project-specific environmental licensing may overlook.

Significance and Claims
The authors claim that their findings underscore the necessity of incorporating historical land-use change into cumulative impact assessments and strategic hydropower planning. The study argues that in tropical river basins, environmental change reflects the accumulation of multiple pressures operating simultaneously. Therefore, effective planning must move beyond regulatory compliance for isolated projects to adopt basin-scale approaches that explicitly consider the territorial context, including the historical trajectory of landscape transformation and the presence of Indigenous Lands. By integrating long-term land-use dynamics with the chronology of hydroenergetic development, this approach provides a more robust basis for balancing renewable energy expansion with long-term socio-environmental sustainability in the Amazon and similar tropical regions.