The Basque hydrologic nowcasting project

Floods are among the world’s deadliest natural disasters with significant social, economic and environmental impacts. In Basque Country, as in other parts of the World with similar geomorphological and hydrometeorological characteristics, flooding events are produced on relatively short spatial and temporal scales (flash floods) making flood modeling a particularly difficult challenge. Major flash floods episodes in Basque Country are produced when rivers react to intense and persistent rainfall that are produced on saturated soils scenarios, occasionally with extra water from snow-melting processes. In this context, nowcasting and very short term forecasting tools (up to 12 hours) are essential in order to manage impact events in real time and to provide different operational products and warning guidance for hydrological, meteorological and civil protection authorities.

In this contribution, we present different aspects in relation to a project, that we have begun in 2021, to implement an operational hydrological nowcasting system for the Basque Country to address the different issues associated with flash floods in the territory and to improve local warning effectiveness. This project is promoted by Basque Government, financed with Basque Water Agency funds in collaboration with the Basque Meteorology Agency (Emergencies and Meteorology Directorate – Security Department). Technical development is performed by meteorological and hydrological experts from Tecnalia (BRTA- Basque Research and Tecnology Alliance) and IHCantabria. One of the aims of this project, in addition to the specific nowcasting technical results, is the generation of hydro-meteorological synergies, where experts from both disciplines can join forces, to combine and exploit expertise, and to accelerate the implementation process of local hydro-meteorological operational systems.

In this paper we focus, not only in technical aspects related with the nowcasting tool we are developing, but in the implementation process itself, where meteorological and hydrological experts join forces and focus on practical local solutions. We introduce the general scheme of the system, describing the functionalities of the main modules and detailing the technical solutions incorporated to deal with the different hydrological and meteorological analysis and prediction needs at different espatio-temporal scales. We describe the pre-processing and post-processing modules paying special attention to the integrated hydro-meteorological analysis and visualization tools. Likewise, we include the description of the validation and verification strategies of the system. We summarize our experience and present some conclusions from workshops and others joint hydro-meteo working sessions that have taken place during the project. In these sessions, the hydrological and meteorological experts have exchanged impressions, forging a joint vision, defining specifications and agreeing on the characteristics that must have a fully useful system for the operational needs and responsibilities of both agencies.