Towards operational flash flood early warning for an arid watershed in Oman based on hydro-meteorological ensemble forecasting

Reliable warnings and forecasts of extreme precipitation and resulting floods are an important prerequisite for disaster managers to initiate flood defence measures. Thus, disaster managers are interested in extended forecast lead times, which can be obtained by employing forecasts of numerical weather models as driving data for hydrological models. Especially in arid environments, warning and forecasting systems are often missing. Challenges arise due to the short response time of watersheds and the uncertainties of the meteorological forecasts. Thus, ensemble forecasts of precipitation are an option to portray these inherent uncertainties.

This study aims to explore the usability of a global numeric weather forecast model for flash flood early warning and present our operational web-based demonstration platform for hydro-meteorological ensemble flash flood forecasting for the Wadi Al-Hawasinah in North Al-Batina region in Oman. We use the ICON-EPS product of the German Weather Service, a global weather forecast model, which provides an ensemble of 40 members each six hours. If predefined extreme precipitation thresholds are exceeded in the region, a rainfall-runoff model tailored on arid hydrology conditions is started to propagate the meteorological uncertainty into the resulting runoff, followed by statistical post processing and visualization for flash flood early warning. Different options for the visualization of the uncertainty information are presented like rainfall quantile maps, exceedance probabilities and traffic light cards. However, the current design of the web-based demonstration platform is based on an iterative stakeholder process, which is still ongoing.

Based on the current setup of the forecasting system, forecast lead times of up to 48 hours are achieved. Furthermore, due to its flexible structure the hydrologic model can be easily exchanged to more advanced 2D-surface routing and inundation modelling approaches.

Besides layout and technical issues, first experiences with the demonstration platform are presented as well as first results regarding forecast performance in this study area as a pilot study. Finally, we discuss the system’s limitations, particularly the absence of real-time observations, and propose potential solutions to address these gaps.