Accuracy assessment of heavy rainfall forecasting in the Western Caucasus with ICON-Eu regional atmospheric model for short-term flood forecasting

Abstract

Heavy rainfalls and rain-induced floods regularly cause substantial damage in the Western Caucasus region. In this study, we assess the accuracy of heavy rainfall forecasting with ICON-Eu regional atmospheric model (developed by the weather service of Germany) and the possibility of its use as input data for rain flood prediction. The main conclusion is that the forecast accuracy is strongly determined by the nature of the rainfall in question (mainly convective or triggered by synoptic-scale processes) and the season of the year. The ICON-Eu model systematically underestimates (by 2-3 times) the precipitation amount in the warm season (April-September) and almost never reproduces local convective heavy rainfall events. Therefore, its forecasts for short-term prediction of summertime rain floods have low efficiency. On the other hand, in the cold season (October-March) the model adequately reproduces heavy precipitation events, with some underestimation of the maximum precipitation amount and overestimation of the coverage area. These forecasts can be used to improve the short-term prediction of flash floods on the rivers of the Black Sea coast of the Caucasus during the period from October to March. In addition, we have performed a detailed analysis of the heavy rainfall and a related flood event which occurred on August 17-18, 2019 by comparing hourly observed precipitation with ICON-Eu and Cosmo-Ru forecasts, as well as applying WRF simulation and rainfall-runoff modelling.