GEANNULEERD Nowcasting and seamless rainfall forecasting for improved (flash) flood early warning

The UN have articulated the ambition that by the end of 2027 no one will be surprised by a flood. Especially for flash flood early warning, this poses quite a challenge as this requires accurate rainfall forecasts with a high spatial and temporal resolution on the local scale. This is still a challenge with numerical weather prediction (NWP) models, but (radar) rainfall nowcasting can provide an alternative to make this possible. This observation-based method, however, quickly loses skill after the first few hours of the forecast due to growth and dissipation processes that are not accounted for in most (advection-based) nowcasting methods. In addition, providing an additional forecasting method can let users drown in the amount of available information. A promising way forward is a seamless forecasting system, which tries to optimally combine nowcasting methods and NWP forecasts. By combining (blending) rainfall nowcasts with NWP forecasts, we can extend the skillful lead time of short-term rainfall forecasts and provide users with more consistent, seamless forecasts.

In this talk, Ruben Imhoff (Deltares) will present recent work on evaluating radar-based nowcasting and seamless forecasting of rainfall for flood early warning. The short-term forecasting chain will be evaluated from observation to discharge forecast. In addition, we will also look ahead, because what do we need in the Netherlands to improve our short-term rainfall and flood forecasts, and how are we going to make this possible in countries where radars and NWP models are absent?

Bio Ruben Imhoff

Ruben Imhoff is a hydrometeorologist working at the operational water management and early warning department of research institute Deltares. Ruben predominantly focusses on short-term hydrometeorological forecasting systems for quickly responding catchments and urban areas, generally using radar-based methods such as nowcasting together with hydrological models. This is also Ruben’s background, as he recently obtained his PhD on rainfall nowcasting for flood early warning at Wageningen University in the Netherlands.