Assessing ensemble flood forecasts with action-relevant scores to support flood preparedness actions: An application to the Global Flood Awareness System in Uganda.
- 1Makerere University, College of Engineering Design Art and Technology, Department of Civil Engineering, Kampala, Uganda (muldouglas99@gmail.com)
- 2Department of Water Resources Monitoring and Assessment, Directorate of Water Resources Management, Ministry of Water and Environment, Uganda.
- 3Department of Electronics, Information, and Bioengineering, Politecnico di Milano, Milano, Italy
- 4Department of Geography and Environmental Science, University of Reading, Reading, UK
- 5Department of Meteorology, University of Reading, Reading RG6 6BB, UK
- 6European Centre for Medium-Range Weather Forecasts, ECMWF, Reading, UK
- 7Red Cross Red Crescent Climate Centre, The Hague, 2521 CV, the Netherlands
- 8School of Geography and the Environment, University of Oxford, Oxford, UK
This study investigates the importance of assessing ensemble flood forecasts with action-relevant scores to support flood preparedness actions by analyzing the discrepancies between traditional general scores that focus on the overall accuracy with other more specific flood event-based scores. Popular general scores such as the Kling-Gupta Efficiency (KGE) or the Continuous Ranked Probability Score (CRPS) are widely used in hydrological modeling and forecasting, but they aggregate different aspects of model quality into a single overall score. On the other hand, flood event-based scores, such as Flood Timing Error (FTE), False Alarm Ratios (FAR) and Probability of Detection (POD), provide more specific verification measures of forecast quality that should be more informative to decision-makers. Both classes of overall accuracy and event-based scores include either deterministic or probabilistic scores, focusing on either the ensemble mean (or quantiles) or on probabilities.
Results are presented for ten catchments in Uganda with different morphological and hydrological characteristics. An evaluation of extended-range re-forecasts from the Copernicus-Emergency Management Service Global Flood Awareness System (GloFAS) has been carried out against observed streamflow data, contrasting overall performance scores, including the KGE and the CRPS, and event-based scores, including the FTE, FAR and POD for forecasts at different lead times (< 45 days). The relative performance of two different versions of GloFAS (2.1 and 3.1) is assessed by this multi-criteria verification setting. Results show that the relative ranking of forecast performance across model versions and catchments may vary based on the scores considered, suggesting that a multi-criteria and event-based evaluation is needed to inform flood preparedness actions.
How to cite: Mulangwa, D., Ficchi, A., Nyenje, P., Sempewo, J., Speight, L., Cloke, H., Harrigan, S., Zaake, B., and Stephens, L.: Assessing ensemble flood forecasts with action-relevant scores to support flood preparedness actions: An application to the Global Flood Awareness System in Uganda., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9862, https://doi.org/10.5194/egusphere-egu23-9862, 2023.
