Flood Forecasting and Warning System

The Flood Forecasting and Warning System of the Sava River basin – Sava FFWS strongly contributes to the strengthening of organizations responsible for hydrometeorological services and flood defense in the Sava countries. The Sava FFWS, as  a common forecasting platform, is an added value to existing national forecasting and warning systems that provides a better level of preparedness and optimized mitigation measures, thereby significantly contribute to reducing consequences of flooding.

The principal objective of the Sava FFWS is to support the stakeholders in taking balanced decisions in emergency situations of floods. The Sava FFWS enables the five riparian countries to take the right management decisions and carry out measures to prevent and mitigate severe flood events, based on accurate forecasts of flows and discharges with a sufficiently long lead time. This requires close cooperation with relevant stakeholders, managing the data and models on country level which is crucial for successful development of the system. The Sava FFWS is of key importance in this cooperation; it is essential to highlight that development of such a system would not have been possible without assistance, active support and outstanding cooperation of all the project beneficiaries in the region.

The Sava FFWS provides the forecasters of the hydrometeorological services an expert tool, enabling them to generate hydrological forecasts based on observed telemetry data from hydrological and meteorological gauges and Numerical Weather Predictions (NWP). The Sava FFWS uses hydrological and hydraulic models to compute the catchment runoff and river flows and water levels.

The Sava FFWS has proven to be a comprehensive system that includes all data and models contributed by the individual countries. This makes it a unique system when it comes to transboundary cooperation on flood forecasting. Nevertheless, there is always a potential for improvements.
The setup of Sava FFWS is modular. The combination of a NWP precipitation and temperature, a hydrological model converting precipitation and temperature to discharge and, in most cases, a hydraulic model routing discharge downstream and computing water levels, define a unique forecast workflow. Due to the number of hydrological models, hydraulic models and numerical weather prediction models available for Sava, several forecast workflows are configured in the Sava FFWS. 

Sava FFWS integrates the following components which are already ‘plugged’ into a common platform and interconnected:

- data hub for the collection of observed data - Sava HIS
various Numerical Weather Prediction models
Within the Sava FFWS, 8 NWP models are used as meteorological inputs:
- model ALADIN1 Croatia
- model ALADIN Slovenia
- model ECMWF2
- model ECMWF ensemble
- model WRF3 Bosnia and Herzegovina
- model WRF Montenegro
- model WRF Serbia
- model NMMB4 Serbia.
[1] Aire Limitée Adaptation dynamique Développement InterNational, http://www.umr-cnrm.fr 
[2] European Center for Medium range Weather Forecasting, https://www.ecmwf.int/
[3] Weather Research and Forecasting model, https://www.mmm.ucar.edu/
[4] Nonhydrostatic Mesoscale Model on B-grid of NOAA, https://nomads.ncep.noaa.gov
Along with the NWPs, the Sava FFWS is prepared to extrapolate radar or satellite imagery in order to provide a very accurate short-term hydrological forecast (nowcasting) for several hours in advance based on measured values. 
Nowcasting products are currently not available within the Sava basin. The first step towards nowcast is to have a radar based composite rainfall image (precipitation field), corrected with observed ground rain gauge data. The radars in the Sava basin are currently not able to produce accurate rainfall images. 
Considering the importance of providing a nowcasting hydrological forecast and raising the awareness of experts to this meteorological input, in the Sava FFWS the Lisca radar data from ARSO (Slovenia) are implemented, next to Opera1 radar composite images. These images are only displayed within the system, but are not connected to any of the hydrological or hydraulic models implemented in the Sava FFWS. This also counts for the H-SAF2 satellite images. 
[1] Radar Programme of EUMETNET, https://www.eumetnet.eu/
[2] Satellite Application Facility of EUMETSAT hsaf.meteoam.it 
Slovenia, Croatia, Bosnia and Herzegovina and Serbia deliver their external hydrological forecasts direct to the Sava FFWS.
Hydrologic Models
The Sava FFWS currently contains 13 hydrological models. Some of them are integrated models including hydraulic component. Some cover complete basin or a large area, others just small local river basins.
The following models cover the complete or the major part of the Sava basin:
- HEC-HMS Sava1  – complete basin (all countries)
- WFlow2 Sava         – part of basin (Bosnia and Herzegovina, Montenegro, Serbia)
The following models are local models:
- Mike-NAM3 Croatia         – integrated in the Mike 11 hydraulic model Croatia
- Mike-NAM Una               – integrated in the Mike 11 hydraulic model Una
- Mike-NAM Vrbas           
- HBV-light4 Bosna             
- WFlow Montenegro        
- HEC-HMS Kolubara
- HBV5 Kolubara
- HBV Jadar
- HBV Tamnava                 
- HBV Ub
- HBV Ljig.    
[1] https://www.hec.usace.army.mil/software/hec-hms/
[2] https://oss.deltares.nl/web/wflow/why-wflow
[3] https://www.mikepoweredbydhi.com/products/mike-hydro-river/hydrology
[4] https://www.geo.uzh.ch/en/units/h2k/Services/HBV-Model.html
[5] http://www.smhi.se/en/research/research-departments/hydrology/hbv-1.90007

Hydraulic models
The Sava FFWS currently contains 30 hydraulic models.
The following model cover the Sava River mainstem:
- HEC-RAS Sava1 (Bosnia and Herzegovina, Croatia, Serbia).
The following models are local models:
- HEC-RAS Bosna
- HEC-RAS Sana
- HEC-RAS Sanica
- HEC-RAS Una (Bihać)
- HEC-RAS Una (Bosanska Krupa)
- HEC-RAS Una (Kulen Vakuf)
- HEC-RAS Usora
- HEC-RAS Vrbas
- HEC-RAS Drina
- HEC-RAS Kolubara        – 17 separate models for Kolubara integrated and merged
- Mike 112 Croatia
- Mike 11 Una
- Mike 11 Vrbas.
[1] https://www.hec.usace.army.mil/software/hec-ras/
[2] https://mikepoweredbydhi.com/products/mike-11
Sava FFWS is based on the Delft-FEWS platform, which has been applied in a number of basins around the world. The platform is flexible and allows integration of all meteorological, hydrological and hydraulic models used in the basin. The system itself is complex, since it is designed in the form of a single central system server and three backups, located in four countries, along with a part of the system (archive and web server) located in the headquarters of the Sava Commission. However, such a system architecture enables active co-operation of all national institutions and at the same time ensures a sense of ownership. The following table lists the beneficiary institutions and the role of each of them in the system, agreed for the first phase of its operational use.
Country Institution Note
Slovenia Slovenian Environmental Agency, Ljubljana Central server
Croatia Croatian Meteorological and Hydrological Service, Zagreb 3rd backup
Hrvatske vode, Zagreb  
Bosnia and Herzegovina Federal Hydrometeorological Service, Sarajevo  
Republic Hydro-Meteorological Service, Banja Luka  
Sava River Watershed Agency, Sarajevo 2nd backup
Public Institution „Vode Srpske“, Bijeljina  
Serbia Republic Hydrometeorological Service of Serbia, Beograd 1st backup and test system
Public Water Management Company “Srbijavode", Beograd  
Montenegro Institute of Hydrometeorology and Seismology, Podgorica  
  ISRBC Secretariat, Zagreb Archive and web server