Spain Reservoir Transparency

Spain has one of the most complete public reservoir datasets in the world. MITECO publishes the Boletín Hidrológico Semanal every Tuesday alongside the BD-Embalses Microsoft Access database covering 401 peninsular reservoirs above 5 hm³ since 1988. In parallel, nine federal SAIH systems (Cantábrico, Miño-Sil, Duero, Tajo, Guadiana, Guadalquivir, Segura, Júcar, Ebro) plus three regional water authorities (Basque Country, Catalonia, Andalusia inner basins) publish their own real-time per-reservoir level and volume readings. SAIH Ebro alone exposes 347 control points across the basin. The ArcGIS dashboard at miteco.maps.arcgis.com provides a national consolidated view. Coverage gaps exist only for the smallest reservoirs (<5 hm³) and some regional systems still publish only via HTML.

Spain's biggest weakness. No REST API anywhere in the public reservoir data stack — the dataset page on datos.gob.es explicitly states 'there is no API for direct connection'. The MITECO historical archive is distributed as a Microsoft Access .mdb file (proprietary legacy format requiring mdb-reader or similar libraries to parse), while the weekly bulletin ships as PDF only. SAIH portals expose data through interactive HTML/ASPX pages that must be scraped, and SAIH Ebro requires user registration to retrieve 15-minute granularity. SAIH Guadalquivir publishes WMS/WFS geoservices but only for station geometry, not time-series volumes. The ArcGIS FeatureServer for embalses contains metadata only (capacity, dam height, location), not fill levels. Reservoirs.earth itself works around this by downloading and parsing the .mdb file with mdb-reader.

Methodology v1.3.0 (capacity-weighted, conservative estimate). Total Spanish national reservoir storage capacity is approximately 63,000-65,000 hm³ when including the long tail of private hydroelectric reservoirs in Galicia/Asturias/Cantabria operated by Iberdrola, Naturgy, Endesa, and EDPR outside the MITECO planning system, plus reservoirs of comunidades de regantes not integrated into SAIH and industrial/mining impoundments. MITECO's BD-Embalses (~401 peninsular reservoirs above 5 hm³, ~56,000 hm³) plus the nine federal SAIH systems plus regional water authorities cover approximately 56,000 hm³. Coverage = round(100 × 56,000 / 64,000) ≈ 88. The major state-managed reservoirs (Alcántara II 3,162, La Serena 3,219, Almendra 2,649, Buendía, Iznájar, Mequinenza, Ricobayo, Alarcón, Cíjara, Valdecañas, etc.) are essentially all covered. The systematic gap is private hydroelectric and small irrigation/industrial reservoirs not in MITECO's federal monitoring perimeter.

Among the deepest reservoir time-series globally. The BD-Embalses.mdb table is literally named 'T_Datos Embalses 1988-2026' — 38 years of continuous weekly per-reservoir storage records, all in a single coherent national dataset rather than fragmented across operators. Individual SAIH systems also retain multi-year sub-daily archives. Only the United States (USGS NWIS, daily records back to 1930s for some gauges) and Norway clearly beat Spain on this dimension; Spain is materially ahead of Portugal (~10 years online) and France (~12 years on the RTE API).

Better than commonly perceived. The national consolidated Boletín Hidrológico is weekly (Tuesdays), but each SAIH publishes its raw measurements at much higher cadence: 15-minute readings are standard across the nine federal systems and are visible on public dashboards (e.g. SAIH Guadalquivir timestamp 'Actualizados 29/05/2026 7:39:49'). For practical purposes, anyone tracking a specific basin can pull near-real-time data; only the cross-basin aggregate has weekly cadence. This is materially better than France (weekly only) and Portugal (weekly only).

MITECO publishes a PDF documenting the BD-Embalses database structure for the 1988-2022 period, and SAIH technical methodology is described in a long-form public document ('El programa SAIH: descripción y funcionalidad'). Each reservoir's capacity and basin assignment is stable and well-identified by CODEMBAL code. The main weakness is that data is marked 'provisional and subject to revision and validation' without a published reconciliation log, and methodological consistency across the nine SAIH systems is implicit rather than enforced by a single technical standard.

MITECO offers an English landing page for the bulletin section, but the substantive content — the weekly PDF, the BD-Embalses field names, the Excel exports, all SAIH portals, and the documentation PDFs — is Spanish-only. The ArcGIS dashboard is Spanish-only. Field names in the .mdb (EMBALSE_NOMBRE, AGUA_TOTAL, AGUA_ACTUAL, CAPACIDAD_TOTAL) require Spanish comprehension. International researchers can navigate the site headers in English but cannot interpret the data without Spanish. Comparable to Portugal (40); much worse than France (80) or the US (100).