Some very general and basic questions on the access and use of the GloFAS map viewer and products are summarised in the table below. Below that, more specific and expert questions are answered in this FAQ. In addition to the FAQ, there is also a Glossary available explaining technical terms frequently used in the GloFAS documentation and complementing this FAQ.

What do I do if I …How to find help
… want to access the GloFAS map viewer?Go to and click on LOGIN to the upper right. Click on “Create an account”, fill in your details and click on “Create account”. You will then receive an email to activate your account.
… don’t remember my log-in information for GloFAS?Go to and click on LOGIN to the upper right. Click on “Forgot Password?”, fill in your email-address and submit. You will then receive a link to reset your password.
… I don’t know what to look at first (there is so much information available)? You can check out section 3.2.3 Getting started using GloFAS in this GloFAS User Guide.
… do not understand the GloFAS forecasts/products?

There is a lot of information available on the GloFAS website to get started with the interpretation and analysis of the GloFAS forecasts. Each layer in the map viewer has a legend briefly describing the content, which can be accessed using the info-button () in the layer list on the left side of the map viewer.

For a more in-depth explanation of the products, the Forecast Wiki and Monitoring Wiki contain detailed descriptions.
… detect an error in GloFAS-IS and want to report it?If you recognise, e.g., a missed event or false alarm in GloFAS or if you suspect a bug with one of the layers in the map viewer, we encourage you to report this issue using the GloFAS contact form. This will help us to improve the system!
… have not found the answer to my question in this list?You can always use the GloFAS contact form to get in touch with us and we will try our best to assist.

Q: What is a numerical weather prediction (NWP) model?

A:  A mathematical model that simulates atmospheric, oceanic, and land processes to predict the weather based on current weather conditions.

Q: Which is the meteorological forecast system in GloFAS?

A: The ECMWF Ensemble probabilistic forecasts are used within GloFAS as meteorological input to the hydrological model to derive the hydrological forecasts. You can read more about the meteorological forcing and the forecasts in the wiki. 

Q: What is a medium-range forecast?

A: Forecasts produced for a lead time of several days (typically 3-15 days)

Q: What is an extended-range forecast?

A: Forecasts produced for a lead time of days 16-30 in the case of the ECMWF ensemble forecast. 

Q: What is a seasonal forecast?

A: Hydrological forecasts produced using seasonal meteorological forecasts, which provide predictions of how the average atmospheric, ocean and land surface conditions over particular areas and periods of time are likely to be different from the long-term average.

Q: What is ensemble forecasting? 

A: A number of simulations (members) using the same meteorological model, but varying the initial conditions and/or the tendencies. The ensemble spread should ideally reflect the model error and is often used to express the uncertainty of a forecast by associating a probability with different forecast values. 

Q: What is the hydrological model in GloFAS?

A: GloFAS uses LISFLOOD-OS as a hydrological model. LISFLOOD-OS is a physically based, semi-distributed hydrological rainfall-runoff-routing model specifically designed to be used in large scale catchments. Detailed information on its specific characteristics and example applications can be found in the online documentation and in the user manual. The LISFLOOD-OS source code is available from GitHUB. 

Q: What is lead time?  

A: Maximum forecast horizon, meaning how far into the future the forecast stretches.

Q: What is forced simulation? 

A: Long-term (> 20-year) hydrological time series simulation forced with reanalyses or reforecasts as proxy data for observations (in GloFAS, data are never generated using observed meteorological forcings). Long-term runs are typically used to generate reference statistics like return period thresholds (see below). One important example of reference statistics is the return period magnitude: forecast simulations are compared to return period magnitudes to generate warnings.

Q: How are the 1.5, 2, 5, 20 years return period thresholds computed?

A: GloFAS flood thresholds are computed from historical (reanalysis) datasets for the period 1979-2019. The reanalysis dataset is forced with ERA5 as meteorological input, not with meteorological observations. The calculated return period values are based on annual maximum series.  

Q: What is a time step? 

A: Time increments for each forecast. A daily time step means that the forecast has a value every 24 hours until the maximum forecast horizon.

Q: What is GloFAS-IS?

A: GloFAS-IS stands for GloFAS Information System consisting of the GloFAS homepage containing background information on the service and the GloFAS Map Viewer that presents all the GloFAS products.

Q: Do the initial conditions derive from satellite data?

A: No. All initial conditions that can be accessed via the Initial conditions menu in the GloFAS map viewer are modelled states of the hydrological model before the date of the forecast run. 

Q: Does GloFAS use and/or predict water levels?

A: No. GloFAS does only predict river discharge and the hydrological model is calibrated on discharge measurements where available. 

Q: Are lakes included in GloFAS and how are they modelled?

A: The largest lakes from the Global Lakes and Wetlands Database are included in the GloFAS model setup, i.e. lakes with a surface area > 100 km2. The names of the included lakes can be found in the "GloFAS lakes and reservoirs” layer under the Static tab in the GloFAS Map Viewer. A full description of the lake routine and modelling is available in the LISFLOOD model documentation. Retention and outflow from lakes is modelled as a function of water level. 

Q: Are dams included in GloFAS and how are they modelled?

A: The reservoirs from the Global Reservoirs and Dams Database are included in the GloFAS model setup. Selection criteria are that there is a significant impact on river discharge and that the reservoir capacity is > 0.5 km3, in short - large reservoirs are included. To check which dams are included in your catchment, please activate the layer "GloFAS lakes and reservoirs” under the Static tab. If you click on the reservoir, the pop-up window will show the main pieces of information. Details on the reservoir modelling within LISFLOOD is explained in the LISFLOOD model documentation. Specific, local operational rules for reservoirs are not included implicitly in LISFLOOD, but the model mimics these operational rules by computing reservoir output as a function of the level of filling of the reservoir.

Q: Is the flood extent predicted in real time?

A: Yes, the flood extent is calculated at 1 km resolution based on the matching of return periods from the GloFAS streamflow forecast, but using a pre-compiled catalogue of modelled inundation extents. No real time hydraulic calculations are done. 

Q: Is it possible to get GloFAS raw data for research purposes? 

A: Yes. In the Data User Guide you can find further information about which data are available, how to download and how to use the data.  

Q: How can I get early notifications on upcoming events like webinars or the annual meeting? 

A: Users can sign-up for the GloFAS mailing list using the GloFAS contact form and stating “I would like to sign-up for the GloFAS mailing list” together with your name, surname and email. 

Q: Is it possible to get a sneak preview on upcoming developments? 

A: Users can register to the stage environment of GloFAS, where planned updates are published in advance of the operational phase of a product. Visit to create an account. Users are furthermore welcome to leave feedback on new products via the GloFAS contact form