Towards an organisational and technical concept for the routine use of radar measurements in a hydrological service

Results from several investigations in North Rhine-Westphalia and in Germany have shown that the routine use of radar data is beneficial for hydrological model applications as well as for on-line applications such as flood warning. Last year, the German Weather Service (DWD) has installed the last radars for the nationwide radar network covering all Germany. Therefore, the State Environmental Agency (LUA) has started the construction of a concept for radar data use which should be capable of serving the needs of on-line data users as well as off-line data applications. The concept is mainly based on the radar data information from the weather service, although informations from other providers can be added.

The objectives for this concept can be summarised in three points:

· Optimal use of existing rainfall measurement data from different sources. Rainfall measurements from raingauge networks usually are not spatially sufficient for detailed analysis of flood events, in particular in summer. A combination with radar data has proven to give significantly better results in model use for both, peak flow and flow volume parameters.

· Gain of experience in radar data use in hydrological services. The hydrological services are still lacking deep knowledge about and experience with use of radar data. Only based on daily experience, the value and the weaknesses of the information inherent in radar data can be estimated.

· Mutual improvement steps in data quality with the German Weather Service. The experience from daily use of the radar data will not only improve knowledge on rainfall for the hydrological services but also - through the feedback to the DWD - increase availability of radar data, its quality and may even cause the creation of other specifically application-oriented radar data products of the DWD.

As "typical" applications have been selected the rainfall-runoff model (off-line) for design purposes through long term simulation combined with fine analyses and flood warning (on-line) in order to protect earlier the valuables than it can be done by the current procedure which is based on the main use of flow level meters (with doppler velocity measuerement at some places).

In order to meet requirements of the services from an organisational aspect, a query at the 12 state sub-agencies and most of the regional water authorities has been conducted. The questions and discussions touched as well the availability of data ("how long will it take until …") and the intended use of the information (integration into models or "just" visual information), and the current practices could be investigated (some services already use - lower quality - radar data from the internet).

For the technical aspects, the use of existing data bases and internet technology as well as the production of "ready-to-use" information were the keywords. The latter describes the fact that the data that are provided at the location of the users are already prepared for the intended application: no reformatting of data, no extra handling with models or tools is necessary before the data are fed into the model or used for flood warning.

The main open questions are today the response time during emergencies, since many (today still unknown) institutions may use the information and the return of experience, in particular in the field of data quality and availability - short: usefulness of radar data for the daily service to the citizens.