Brazil Reservoir Transparency

Brazil publishes operational reservoir data through multiple complementary streams. ONS exposes daily and hourly hydrological series (Energia Armazenada — EAR, Energia Natural Afluente — ENA, useful volume per reservoir, subsystem, basin and equivalent energy reservoir) as open CSV / XLSX / Parquet files on dados.ons.org.br and the AWS S3 bucket ons-aws-prod-opendata (sa-east-1), under CC-BY 4.0 and without authentication. ANA's SAR (Sistema de Acompanhamento de Reservatórios), live since 2014, organises three modules: SIN (160 hydroelectric reservoirs of the National Interconnected System), Nordeste/Semiárido (500+ reservoirs across nine northeastern states and Minas Gerais, totalling ~40 billion m³) and Outros Sistemas Hídricos (Cantareira serving São Paulo, the Federal District system, Paraopeba). ANA also issues a daily PDF Boletim Diário from its Sala de Situação for the SIN reservoirs. HidroWeb / SNIRH publishes hydrometric series for thousands of fluviometric and pluviometric stations. The third-party R package reservatoriosBR aggregates 713 ANA-tracked reservoirs and 39 ONS-tracked reservoirs into a single, tidied interface, confirming the underlying breadth of public data. This is among the most extensive reservoir data ecosystems in the world by scope.

Multiple machine-readable access paths exist. The ONS S3 bucket is openly readable (aws s3 ls --no-sign-request s3://ons-aws-prod-opendata/) with CSV, XLSX, Parquet and JSON data dictionaries. The HidroWeb REST API at snirh.gov.br/hidroweb/rest/api/ provides telemetric station queries and historical series downloads (e.g. /estacaotelemetrica?id=, /documento/gerarTelemetricas), though obtaining a token requires submitting an access request at /hidroweb/acesso-api. dadosabertos.ana.gov.br exposes an ArcGIS Hub catalog with a Search API and per-dataset REST MapServer endpoints, and ANA publishes metadata records through GeoNetwork at metadados.snirh.gov.br. ANA SAR tables include a CSV export button. Mature open-source wrappers exist (the R package reservatoriosBR on CRAN/GitHub, multiple Python and Java clients on GitHub). The remaining friction points: SAR itself has no documented REST endpoint (data must be scraped per-table or obtained via the wrappers), the daily ANA SIN bulletin is PDF-only, the legacy Telemetria 1 WebService is being retired (deadline extended to 30 June 2026) and the new HidroWeb API still gates access behind a request form. The S3 bucket model and the HidroWeb REST API together still place Brazil clearly above the regional median for programmatic accessibility.

Conservative estimate — denominator includes private mini-hydro in Amazonas and other northern states, small municipal reservoirs in the South and Centre-West not in the SIN dispatch or semi-arid programme, private agro-industrial impoundments, and substantial uncertainty in sedimentation-corrected capacity curves for older facilities. Methodology v1.3.0 (capacity-weighted). Covered capacity through ONS (160 hydroelectric reservoirs of the SIN, essentially the entire dispatchable hydropower fleet) + ANA SAR (500+ semi-arid water-supply reservoirs + Cantareira, DF, Paraopeba), aggregated via reservatoriosBR's 713 reservoirs, totals approximately 570,000 hm³. A realistic national denominator including private mini-hydro in Amazonas, southern municipal/agricultural reservoirs and unaccounted sedimentation tail reaches approximately 715,000 hm³. Score = round(100 × 570,000 / 715,000) = 80. Brazil's strategic dispatchable and semi-arid storage is exceptionally well covered; the conservative discount reflects the long tail of private/municipal storage outside SIN and the semi-arid programme, plus systematic capacity uncertainty.

Historical reach is one of Brazil's strongest dimensions. ONS maintains the official Base de Dados Técnica feeding long-term energy planning models (NEWAVE, DECOMP), with monthly ENA/EAR series for the SIN going back to 1931 for the reconstituted historical hydrological record used in stochastic dispatch optimisation. Daily reservoir hydrological data on the open portal cover the modern operational period in continuous machine-readable form. The reservatoriosBR aggregation exposes ANA-sourced series 'from 1980' as a default and ONS subsystem series from 2000 onwards. HidroWeb hosts the National Hydrometeorological Network with fluviometric records extending in some cases to the 1920s–1940s for legacy stations. ANA SAR archives daily bulletins from its 2014 launch, providing 12 years of validated daily reservoir data for the SIN and northeastern reservoirs. The main limitation is that very long historical series (pre-1980) are most easily obtainable in research-grade aggregated form (e.g. the 1931-onwards series used in dispatch models) rather than as daily reservoir-level open files; pre-2000 daily fill percentages per reservoir require a degree of post-processing.

ONS publishes reservoir hydrological data on a daily basis (dataset 'Dados hidrológicos de reservatório — Base Diária') and on an hourly basis (dataset 'Base Horária'), with the cadastral dataset refreshed twice daily at 12:00 and 19:00 BRT. ANA SAR refreshes automatically as ANA receives operator data, and ANA publishes a daily PDF Boletim Diário from the Sala de Situação for the SIN reservoirs. CEMADEN's complementary telemetric network (3,500 rain gauges and 301 hydrological stations) reports every 10 minutes nationwide for hydrometeorological alerts. Combined daily-or-better cadence with hourly storage series for the hydro fleet and 10-minute telemetry for the alert network is among the highest update frequencies of any national reservoir-monitoring regime, comparable to Spain's daily embalses portal and ahead of most peers.

Documentation has improved substantially. ANA publishes a public SAR manual (manual-sar_v1-0.pdf) describing data sources, variables and computation of useful volume. The SNIRH GeoNetwork (metadados.snirh.gov.br) hosts ISO-19115 metadata records for the reservoir catalogue, including capacity, datum, basin and operator attributes. ONS provides a per-dataset data dictionary in PDF and JSON for each open data product and publishes operating policy documents (Procedimentos de Rede). Capacity figures, minimum operating levels and stage-volume relationships used in the EAR computation are documented in the dispatch models distributed publicly with NEWAVE/DECOMP decks. Limitations: sensor-level uncertainty bounds and bathymetric resurvey schedules are not consistently published per reservoir; cross-walking between ONS plant codes and ANA/SNIRH station codes still requires manual mapping; documentation is dispersed across multiple agencies rather than consolidated in a single canonical reference.

All primary portals — dados.ons.org.br, ana.gov.br/sar, snirh.gov.br/hidroweb, gov.br/ana, dadosabertos.ana.gov.br, cemaden.gov.br — are exclusively in Portuguese, including dataset titles, field descriptions, data dictionaries, the SAR manual and the daily SIN bulletin. No English UI is offered on the main data interfaces. The AWS Open Data Registry listing for the ONS portal is in English and provides an entry point that international users can discover, and the underlying CSV/Parquet field names are language-neutral once a user becomes familiar with the schema. Several scientific publications (e.g. the harmonised Brazilian power-system dataset paper in Scientific Data, the EIA Brazil country brief) provide English-language secondary documentation of how the ONS data are structured. Brazil scores slightly above the typical Latin American floor on this dimension thanks to the AWS registry entry and a published English-language scientific record describing the open data assets, but the operational experience for a non-Portuguese speaker remains friction-heavy.