Sweden Reservoir Transparency

For the COVERED subset (~30 individual reservoirs occasionally exposed via Vattenfall, Fortum, Statkraft and SMHI Vattenwebb river-system pages), publication is partial and inconsistent. Svenska kraftnät publishes aggregate weekly storage at the national level and for 4 regional zones, covering ~90% of national hydroelectric capacity in volume terms but with zero per-reservoir granularity. SMHI publishes river discharge through its open data API but does not expose reservoir storage as a managed variable. The handful of individual reservoirs that appear in operator pages typically have only seasonal or annual context rather than continuous storage time series. The typical covered reservoir does not have routine volumetric storage published.

For the COVERED subset, no per-reservoir REST API exists. Svenska kraftnät publishes weekly aggregates as an HTML table and a downloadable Excel/CSV file — machine-readable, but only at national and 4-region aggregate granularity (i.e. it does not technically address the covered individual reservoirs). SMHI's open data API (opendata.smhi.se/apidocs/hydroobs/) covers meteorology and river observations with documented JSON endpoints but explicitly excludes reservoir storage. Raw operational data sits with private hydropower companies that have no data-sharing obligations under current Swedish regulation. For an analyst seeking per-reservoir Swedish storage, the only feasible pathway is direct contact with operators.

v1.3.0 capacity-weighted with conservative estimation applied 2026-05-29. Sweden's total hydropower reservoir capacity above 10 hm³ is approximately 33,000 Mm³, concentrated in the large Lapland storage reservoirs (Suorva/Akkajaure, Tjaktjajaure, Satisjaure, Letsi, Stora Lulevatten, Sitasjaure), the mid-Norrland systems (Höljes, Trängslet, Storrösjön) and the major regulated lakes (Vänern, Storsjön, Siljan). Vattenfall and Fortum expose a subset of marquee reservoirs through operator dashboards and routine reporting — partial public reach covers approximately 7,260 Mm³ on a conservative basis. Coverage = round(100 × 7,260 / 33,000) = 22. The conservative downward revision from 30 reflects that even within the covered marquee reservoirs the typical disclosure is sporadic to monthly rather than continuous, that the long tail of small private hydropower reservoirs has no legal obligation to publish, and that Svenska kraftnät's aggregate weekly figure spans ~90% of national storage in GWh terms but provides zero per-reservoir granularity and is excluded from capacity-weighted covered total.

MEDIAN history for the COVERED subset is approximately 3–5 years of accessible per-reservoir series. Most covered reservoirs lack any continuous public time series; what exists is typically a rolling window of recent operator updates. SMHI river discharge series extend many decades for some gauging stations but are not reservoir storage and are not in the covered population. Svenska kraftnät's aggregate weekly series goes back to ~2002 (20+ years), but that is the MAX for aggregate data — the median covered individual reservoir has no comparable continuous record.

For the COVERED subset, the typical cadence is sporadic to monthly. Svenska kraftnät updates the national/regional aggregate weekly, but as established under coverage scoring the aggregate is not per-reservoir. Operator pages from Vattenfall, Fortum and Statkraft are updated irregularly. SMHI's hydroobs API updates daily but for river/meteorological variables, not reservoir storage. The typical covered reservoir does not receive a defined update cadence at all.

Svenska kraftnät documents the regional boundaries used for the 4 zones and publishes total capacity per region, enabling percentage-full calculations at the aggregate level. The methodology for aggregating from individual reservoirs to regions is described at high level only; the capacity figures used, the weighting of individual reservoirs and the exact stations included are not published. For the COVERED individual reservoirs, neither stage-storage curves nor operational rule curves are publicly documented. SMHI's hydrology documentation is thorough for river flow but not relevant to reservoir storage. ICOLD entries provide capacity figures for many of the larger Swedish reservoirs but not operational methodology.

Svenska kraftnät publishes the reservoir statistics page in Swedish only, though the data itself (numbers in a table) is language-agnostic. SMHI's open data API is well-documented in English. Sweden has very high English proficiency nationally, and key energy statistics are often available in English through other channels (e.g., Energimyndigheten annual report, Vattenfall and Fortum group pages). The effective usability for an international researcher is moderate-to-strong — the data can be found and downloaded but requires navigating a Swedish-language interface for the SVK aggregate.