Flood-risk data sources in Slovakia: official maps, hydrology and terrain

Who produces flood-risk data in Slovakia

Slovakia's flood record is produced by three public institutions with distinct roles. Slovenský vodohospodársky podnik, š. p. (SVP), the state enterprise that manages the water-management-significant watercourses, prepares the flood hazard maps (mapy povodňového ohrozenia) and flood risk maps (mapy povodňového rizika). The Ministry of Environment (MŽP SR) is the competent authority: it runs the preliminary flood risk assessment, approves the maps and the flood risk management plans, and reports them to the European Commission. The Slovak Hydrometeorological Institute (SHMÚ) operates the gauging network, issues hydrological forecasts and warnings, and holds the discharge statistics that the mapping depends on.

The legal spine is Directive 2007/60/EC on the assessment and management of flood risks, transposed into Slovak law by Act No. 7/2010 Z. z. on flood protection. The directive prescribes three products every six years: a preliminary flood risk assessment that identifies areas of potentially significant flood risk, flood hazard and flood risk maps for those areas, and flood risk management plans. Slovakia is now in the third planning cycle, with the 2024 assessment published in December 2024 and the updated maps due by 22 December 2025.

The SVP maps show flood extent lines (záplavové čiary) for five scenarios, Q5, Q10, Q50, Q100 and Q1000, each carrying water depth in meters and flow velocity in meters per second as attributes. They were built with hydrodynamic modeling (the MIKE Flood family) and are published on the SVP map portal at a 1:10 000 working scale, with a WMS layer registered in the national spatial data registry. The flood risk maps overlay the exposed population, economic activity, industrial installations that could pollute, drinking-water intakes, bathing waters and NATURA 2000 sites.

One limit matters more than any other. Official Slovak maps exist only for the areas identified in the preliminary assessment: 202 geographical areas in the 2024 update, of which 126 have an existing significant risk on a watercourse reach and a further 24 a probable one. The Váh basin alone accounts for 82 of those areas. Everywhere else there is no official Slovak flood map, and that gap is where European layers, national terrain data and modeling take over.

The Floods Directive cycle in Slovakia

Directive 2007/60/EC entered into force on 26 November 2007 and set three deadlines, each repeated every six years. Slovakia's first assessment was completed in 2011, the first maps in 2013 and the first plans in 2015; the second cycle refreshed all three, and the third cycle is under way. The 2024 assessment used 1997 to 2023 as its reference period and, for the first time, derived the candidate areas from hydrodynamically modeled Q100 extents rather than indicative flood lines alone.

Deadlines from Directive 2007/60/EC Articles 4, 6, 7 and 14, as restated in the Slovak preliminary flood risk assessment 2024.

Source inventory

The table lists every public dataset a flood-risk analysis of a Slovak address can draw on, from the official national maps to the European and satellite layers that fill in the unmapped reaches. Where a publisher does not state a license on the pages we checked, the license column says so rather than guessing.

Compiled from the publishers named in the sources list; resolution and license as stated by each publisher.

What the five scenarios mean

A return period is a long-run average, not a schedule: a Q100 flood has roughly a 1 in 100 chance of being equalled or exceeded in any given year. The directive asks for three probability classes and lets each country choose the exact return periods. Slovak law fixes the low-probability scenario at a flood recurring on average once in 1,000 years or less often, the medium at about once in 100 years and the high at about once in 10 years, and SVP adds Q5 and Q50 for finer grading. There is no Q20 layer on the Slovak maps, which is worth knowing when comparing with neighboring countries.

Scenario classes from Directive 2007/60/EC and Act No. 7/2010 Z. z. §6; scenario list from the SVP hazard maps as republished by the Košice self-governing region.

Terrain: DMR 5.0 and what it changes

Every flood map is only as good as the ground it is drawn on, and Slovakia's ground is unusually well measured. The Úrad geodézie, kartografie a katastra SR (ÚGKK) scanned the entire country with airborne LiDAR between 13 November 2017 and 25 June 2022 in 42 lots, and completed the derived terrain model, DMR 5.0, on 31 May 2023. The specification required a point density of at least 5 points per square meter and a height error of no more than 0.25 m for the model; the achieved values were far better, with last-return densities between 15 and 52 points per square meter and DMR 5.0 height errors between 0.02 and 0.16 m depending on the lot.

The products are a 1 m bare-earth raster (DMR 5.0), a 1 m surface model that includes buildings and vegetation (DMP 1.0), and classified point clouds. Since 1 July 2023 the whole-country ZIP packages have been downloadable free of charge, the license was changed to CC BY 4.0 with attribution to ÚGKK SR, small extracts can be exported from the ZBGIS map client, and WMS services followed. A second scanning cycle started in 2022 with a tighter specification (at least 15 points per square meter, 73 lots over roughly twelve years), so the terrain will keep improving.

For flood work the terrain model does three jobs. It defines the floodplain geometry that hydrodynamic models such as those behind the SVP maps route water through. It lets a model resolve small streams and local depressions that a 30 m global model smooths away; the Copernicus DEM GLO-30, with a vertical error below 4 m at 90 % confidence, is a fallback rather than a substitute. And, because raised linear features such as embankments show up at 1 m, it allows flood defenses to be traced where no register of levees exists.

European and satellite layers

The JRC river flood hazard maps for Europe and the Mediterranean Basin (Dottori et al., 2022) are the most used pan-European layer. They give flood extent and depth at 100 m for return periods of 10, 20, 50, 100, 200 and 500 years, produced with the LISFLOOD hydrological model and the LISFLOOD-FP hydraulic model that also power EFAS, and they are published under CC BY 4.0. Two caveats govern their use in Slovakia: they cover rivers with an upstream drainage area above 500 km², so the Danube, Váh, Hron, Hornád, Bodrog and their larger tributaries are in but the small streams that cause most Slovak flash floods are not, and they are undefended, meaning dykes and other local defenses are ignored. The JRC itself states they are not an official flood hazard map.

The European Flood Awareness System (EFAS) is the forecasting arm of the Copernicus Emergency Management Service. The JRC is the entrusted entity and ECMWF runs the hydrological forecast computational centre; the system produces river flood probabilities up to 15 days ahead, flash-flood indicators and seasonal outlooks up to four months. It is an early-warning product for authorities rather than a hazard map, but its climatological return-period thresholds are what the JRC maps and many national services calibrate against.

Observed floods come from the Copernicus Emergency Management Service. Rapid Mapping delineates flooded areas for activated events, and Global Flood Monitoring processes every Sentinel-1 radar pass into a systematic flood archive that reaches back to 2015. After Storm Boris the Ministry of Environment republished the Copernicus flood-extent maps for the Morava, Myjava and Danube basins on the national geoportal, which makes September 2024 the best-documented recent event for validating any Slovak model. The EU-Hydro river network and the EEA Flood Risk Areas Viewer, which shows the areas each member state has reported under the directive, complete the European set.

Reference floods in the public record

The 2024 preliminary assessment is also the best single chronicle of Slovak floods, with a year-by-year rainfall and flood account for 1997 to 2023 and a tally of days on which a flood activity level was declared. Two events anchor most discussions. The May and June 2010 floods followed the wettest year in the record, with annual precipitation of 1,255 mm, 165 % of the long-term normal, and a May total of 235 mm, 309 % of the monthly normal, that triggered flooding across almost the whole country. Storm Boris in September 2024 pushed the Danube at Bratislava to 970 cm on 17 September, flooded Devín, Devínska Nová Ves, Stupava, Pezinok and Jablonica, and was the first major event fully captured by Copernicus satellite mapping in Slovakia.

MŽP SR, Predbežné hodnotenie povodňového rizika v SR, aktualizácia 2024; Wikipedia, 2024 Central European floods.

How to check a Slovak address

A defensible flood-risk view of a single property takes six steps, each tied to one of the sources above.

1. 1

   Find the district on the SVP portal

   Open the SVP map portal, pick the okres, and locate the parcel. If the parcel is inside a mapped area you will see up to five flood lines; read the depth and velocity attributes at the building footprint, not at the plot boundary.

2. 2

   Read Q100 first, then Q1000

   Q100 is the reference scenario that the risk-area register, planning practice and most underwriting rules use. Q1000 tells you the residual worst case, which matters for basements, critical services and anything behind a dyke.

3. 3

   Check whether the reach is in the 2024 register

   Search the preliminary assessment for the watercourse and municipality. A reach listed with existing significant risk has been flooded in the reference period or modeled as floodable at Q100; a reach absent from the register has no official map at all, which is not the same as no risk.

4. 4

   Look at the gauge and the warnings

   On the SHMÚ site find the nearest gauging station and the current hydrological warning degree. The flood activity levels defined in the municipal flood plan tell you at which stage the local response starts.

5. 5

   Fill unmapped reaches with European layers

   For large rivers outside the register use the JRC 100 m maps, remembering they ignore defenses. For small streams there is no ready-made map; a terrain-based model on DMR 5.0 is the only option.

6. 6

   Validate against observed floods

   Compare any modeled extent with the Copernicus maps of September 2024 or with the flood chronicle in the assessment. A map that misses a documented flood is wrong, whatever its return period says.

How a model combines these sources

A property-level flood model treats the official maps as ground truth where they exist and as calibration targets where they do not. Bytero's approach is to route modeled discharges over the 1 m national terrain, attach the SVP scenario lines and the 2024 register where an address falls inside a mapped reach, use the JRC layers for the large rivers, and score the result against satellite-observed floods such as September 2024 before any figure is published. Availability by market is listed on the coverage page.

Questions