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On 14th May in Serbia and Bosnia heavy rain between 40 and 130 mm just in 24h was recorded. From the few stations in Serbia displayed on the plot below we can see that 24-hour accumulations exceeded the 99th percentile of the observed 15-year climate. The most extreme precipitation was observed in Loznica, a station in western Serbia at the border with Bosnia where 129 mm were recorded on 14th May whilst the climate maximum is just 68.4 mm. Comparing the forecast with observations we can notice that 7-days in advance the tail of the forecast consistently predicted extreme values of the rainfall but the forecast was uncertain and therefore EFI values were positive but not high whilst SOT was positive indicating a possibility of an extreme event. Approaching the day of interest forecast CDFs became more extreme ending up with really extreme CDF in the most recent forecast on the day of the extreme rainfall. We can also notice that the forecast underestimated the rainfall totals even for the most extreme members but at the same time such an extreme rain as observed in Loznica seem locakizedlocalized. All the other stations around measured rainfall amounts between 40 mm and just above 100 mm which is close to the rainfall in the most extreme ensemble members.
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The plots below show the CDFs for the TIGGE forecasts from the plots above (3-day precipiation precipitation for the area).
Gallery includeLabel cdf_3d_area sort comment title 3-day precipitation for area
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The figures above show the modelled flow for river Sava, close to Beograd. The peak flow appear around 18-19 May, with a flow of 6500-7000 m3/s in the EFAS system (corresponding to 500 ~500 years return period). Already the longest forecast covering this date (9 May) had a number of ensemble members with return period >20 years. After the rain fell 14-15 May the uncertainty got minimal (as the flood model for the initial conditions is driven by observed precipitation).
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- Good early detection of the large scale cut-off low and extreme precipitation (in EFI)
- Early response in the EFAS system
- Precipitation amounts clearly underestimated for Beograd. ECMWF worse than other centres.
- Only the very last forecast captured the amount over Beograd.ECMWF ensemble too diffuse for this case?
6. Additional material
Information sheet from JRC/EFAS 16 May
Analysis of the event by NOAA.
Discussion in Daily Repot Report about the calculation of EFI (http://intra.ecmwf.int/daily/d/dreport/2014/05/20/sc/)