201405 - Rainfall - South-eastern Europe

 Status:Ongoing analysis Material from: Linus Mohamed, Florian

Discussed in the following Daily reports:

http://intra.ecmwf.int/daily/d/dreport/2014/05/08/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/09/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/12/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/13/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/14/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/15/sc/

http://intra.ecmwf.int/daily/d/dreport/2014/05/16/sc/

1. Impact

The rainfall was caused by a cut-off low over south-eastern Europe. The period running up to the event had been wet and the soil was already saturated before the rain event, where the worst areas got more than 200 mm over 3 days.

On 16 May, the Bosnia - Herzegovina and Serbia requested assistance through the EU Civil Protection Mechanism. Serbia declared a state of emergency on Thur 15 May.

This is a list of new items on the event:

http://www.reuters.com/article/2014/05/15/us-balkans-flood-idUSBREA4E0PA20140515

http://www.bloomberg.com/news/2014-05-15/flood-hit-serbia-seeks-aid-from-russia-eu-in-record-rain.html

http://www.bbc.co.uk/news/world-europe-27459184

The figures above show warnings on Meteoalarm for the 14 and 15 May. Red warnings where issued for rainfall in Serbia, Bosnia - Herzegovina, Austria and Slovakia.

2. Description of the event

The figures below show the analyses of t850 and z500 (00UTC). The rainfall was caused by a cut-off low situated over south-east Europe, bringing moist winds from east, hitting the mountains on Balkan.

The month before the event had been wet and the ground was already saturated in the area, as seen in the figures below.

Above is the radar sequence from the Romanian Met Service for a part of 14 May, showing the persistent rainfall over Serbia and parts of Romania.

The figures above show the observed precipitation for the 14,15, 16 and 17 May (06-06) and the HRES forecast (day 2-3). The forecast underestimated the precipitation in the worst affected areas.

The table below shows the observed precipitation for Loznica (13262, 44.3N, 19.1N), Beograd (13274, 44.9N, 20.3E) and Valjevo (13269, 44.2N, 19.5E). The precipitation is the 24-hour observed at 06UTC. The total for the 5-day period was for Loznica 219 mm, Beograd 190 mm and Valjevo 199 mm.

The connection to the system giving all the rain, high wind gusts where measured, especially in the Slovakian mountains with wind gusts of more than 40 m/s.

3. Predictability

3.1 Data assimilation

3.2 HRES

The plots below show z500 and t850 forecasts from HRES, all valid at 00UTC on 15 May. The first plot is the analysis. The large-scale cut-off low was very well predicted.

The nest plots show the same forecasts but for MSLP and precipitation.

As seen above, the precipitation in the worst affected areas seems to have been underestimated.

The figures above show the precipitation verification for 14 May 06UTC - 15 May 06UTC for forecast from 12, 13 and 14 may 00UTC. Only the very last forecast captured the observed rainfall amounts.

The figures above show the precipitation verification for 15 May 06UTC - 16 May 06UTC for forecast from 13, 14 and 15 may 00UTC. Here the extreme precipitation over the orography in Austria and Slovakia was underestimated.

3.3 ENS

The plots above show the EFI for a 5-day period (12-17 May for all but the last plot where the period is shifted 1 day). The signal is present already from the longest forecast presented here (from 8 May) and gets stronger as the event approaches.

The plots above show the EFI for 14 May (the day with the heaviest precipitation in Serbia) from different initial times.

The figure above show the CDF for Beograd, valid the 14 may. The observed precipitation for that day (0-0 UTC) was 112.6 mm (station 13274). The last forecast was more extreme than the earlier, but still underestimated the rain.

3.4 Monthly forecasts

Coming soon.

3.5 Comparison with other centres

The plots below show CDF for 5-day precipitation 12 May 06UTC to 17 May 06UTC for Beograd (point for 44.9N, 20.3E), for different centres obtained from the TIGGE archive. The observed value for the period was 190 mm.

The plots below show CDF for 3-day precipitation 13 May 06UTC to 16 May 06UTC for Beograd, for different centres. The observed value for the period was 174 mm.

The plots below show CDF for 3-day precipitation 13 May 06UTC to 16 May 06UTC for Loznica (point for 44.3N, 19.1E), for different centres. The observed value for the period was 213 mm.

The plot below shows the CDF for 14 May 06UTC to 15 May 06UTC for Beograd. On this short lead time only NCEP got high precipitation amounts (108 mm was observed).

For this point, the ECMWF forecast was generally worse than for other centres, but might captured the signal one day earlier (8 May). We have to check whether the differences can be due to difference in orography. Optimally, the diagnostics should be done for an area average.

3.6 EFAS

The figures above show the sites where the alert levels are reached in the EFAS forecasts. The colour of the circles corresponds to different return periods (purple>20 years).

The figures above show the modelled flow for river Sava, close to Beograd.

4. Experience from general performance/other cases

• The flooding in central Europe 2013. Technical Memorandum soon finished about the case.

5. Good and bad aspects of the forecasts for the event

• 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.

6. Additional material

Information sheet from JRC/EFAS 16 May

Analysis of the event by NOAA.