Severe floods occurred in the Georgian capital Tbilisi, on 14 June after very heavy rainfall.
22 October 2020
13 June 2015
By Ivan Smiljanic (DHMZ )
Overflowing rivers in Tbilisi caused flooding and landslides in the centre of the Georgian capital, leaving the city devastated and occupied by the animals who broke out of the local zoo. At least 19 people were reported to have died.
The weather conditions that led up to the flooding were a series of convective rainfall events occurring for a few days.
The favourable conditions for these convective activities were connected to an upper level trough that slowly approached the region from the west — shown by the green isolines of geopotential height at 500 hPa pressure level (Figure 1).
The same image contains the black isolines of MSLP (mean sea level pressure) overlaid on a SEVIRI 10.8 µm infrared image. At the lower levels there is no prominent pressure pattern as there is aloft.
The downpour which might have caused the rivers in the area to overflow was a relatively small and short convective event that occurred on the evening of 13 June, as shown in the Meteosat-10 infrared animation .
Although the infrared imagery from geostationary satellites reveals that the position of the storm was north of the capital, parallax correction needs to be taken into consideration — meaning that the true position of the storm is approximately 10–20 km south of the position on the image.
Figure 2 reveals this parallax effect by presenting the same scene from the two satellites, at the same time, positioned over two different points of the Earth’s equator — Meteosat-7 (Indian Ocean) and Meteosat-10 (Atlantic Ocean, Gulf of Guinea).
The measured difference between the same core of the storm, seen from the two different satellites, is approximately 25 km.
Although the nominal pixel area of the Meteosat-7 MVIRI instrument is lower (5x5 km), for the region of Georgia, pixels of the two different satellites are almost comparable in size.
The Meteosat-10 SEVIRI instrument nominally has a better resolution (3 km), but it is further away from the area of interest (Figure 3).
Subsequent information from Ayhan Sayin, Scientific Officer Hydrological Forecasting and Water Resources Division, World Meteorological Organization supports the information in the satellite imagery above.
The WMO project called Flash Flood Guidance System (FFGS) uses meteorological satellites precipitation data, including MSG, to generate a number of warning products. The Satellite Precipitation product (GHE) estimated that there would be 100 mm of rainfall in 24 hours in Georgia. Also, flash floods warning products (PFFT) were generated for the Georgia area.
Nervous Searchers Help Flood Victims, Watch for Escaped Zoo Animals in Tbilisi (NBC News)
Georgia floods: Hippo, bear found on streets as animals escape Tbilisi zoo (The Indian Express)
2015 Tbilisi flood (Wikipedia)
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