შრომები, ISBN 978-9941-36-147-0, თბილისი, საქართველო

Abstract

Precipitation of more than 100 mm per day falls very rarely in Tbilisi (several cases in the last 120 years). On August 29, 2023, this incident repeated itself. In this work an analysis of this rare phenomenon for Tbilisi is presented.

Full text

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საერთაშორისო სამეცნიერო კონფერენცია „დედამიწასა და მის გარსებში მიმდინარე გეოფიზიკური პროცესები“
შრომები, ISBN 978-9941-36-147-0, თბილისი, საქართველო, 16-17 ნოემბერი, 2023 წ.
International Scientific Conference "Geophysical Processes in the Earth and its Envelopes"
Proceedings, ISBN 978-9941-36-147-0, Tbilisi, Georgia, November 16-17, 2023
ANALYSIS OF STRONG PRECIPITATION IN TBILISI ON
AUGUST 29, 2023
*Beglarashvili N.,**Jamrishvili N., ***Janelidze I., *,** Pipia M., **Tavidashvili Kh.
*Institute of Hydrometeorology of Georgian Technical University, Tbilisi, Georgia
** Mikheil Nodia Institute of Geophysics of Ivane Javakhishvili Tbilisi State University, Tbilisi, Georgia
***Georgian Technical University, Tbilisi, Georgia
beglarashvilinani@yahoo.com
Abstract:
Precipitation of more than 100 mm per day falls very rarely in Tbilisi (several cases in the last 120
years). On August 29, 2023, this incident repeated itself. In this work an analysis of this rare phenomenon for
Tbilisi is presented.
Key Words: atmospheric precipitation, flooding, flood.
Introduction
The study of the intensity and distribution of precipitation in Georgia has always been the most pressing
problem among known atmospheric phenomena [1-5]. This has become even more relevant against the
background of the ongoing process of climate warming [6]. Heavy precipitation leads to floods, landslides,
mudflows, damage to vegetation, etc. [7-10]. Their deficiency contributes to droughts, desertification, decreased
agricultural yields and other negative processes [6,7].
Floods due to heavy rainfall most often occur in western Georgia, although in its eastern part, including
Tbilisi, these processes are not so rare [7-9]. For example, a heavy rainfall in the vicinity of Akhaldaba (a suburb of
Tbilisi) led to a landslide, which subsequently provoked a catastrophic flood in Tbilisi on June 13-14, 2015 [10-12].
Floods due to heavy rainfall most often occur in western Georgia, although in its eastern part, including
Tbilisi, these processes are not so rare [7-9]. For example, a heavy rainfall in the vicinity of Akhaldaba (a suburb of
Tbilisi) led to a landslide, which subsequently provoked a catastrophic flood in Tbilisi on June 13-14, 2015, and
were 20 people confirmed dead [10-12; https://en.wikipedia.org/wiki/2015_Tbilisi_flood].
Precipitation of more than 100 mm per day falls very rarely in Tbilisi (several cases in the last 120 years
[5,12]). However, on August 29, 2023, this incident repeated itself. Below is an analysis of this rare phenomenon
for Tbilisi.
Study area, material and methods
Study area – Tbilisi. The following information are used.
Data of Georgian National Environmental Agency, Hydrometeorology Laboratory of Tbilisi State University
and satellite observation data [https://neo.gsfc.nasa.gov/view.php?datasetId=GPM_3IMERGM] about the daily sum
of atmospheric precipitation
Data on vertical atmospheric sounding [https://www.ready.noaa.gov/index.php] for calculated of Indexes of
Stability of the Atmosphere [http://weather.uky.edu/about_totl.htm].
Lightning data from [https://www.blitzortung.org/ru/live_lightning_maps.php?map=42].
In this work Total Totals Index (TT) and K Index stability of the atmosphere are used.
TT =
T
850 +
T
d850 -
2·T
500
; K = T
850
- T
500
+ T
d850
- T
700
+ T
d700,
in degrees C.
where
T
represents temperature and
T
d
represents dew point temperature at the indicated level (500, 700, and
850 mb).

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Results and discussion
Results in Table 1 and Fig. 1-3 are presented.
In Table 1 data about TT and K Indexes for Tbilisi from 04 hour, 29.08.2023 to 01 hour, 30.08.2023 are
presented.
Table 1. TT and K Indexes for Tbilisi from 04 hour, 29.08.2023 to 01 hour, 30.08.2023.
Time/Date TT Qualitative Assessment
K
Qualitative Assessment
04.29.08.2023 48 Scattered Thunderstorms/Isolated
Severe. 33 Numerous Thunderstorms. Heavy rain.
07.29.08.2023 48 Scattered Thunderstorms/Isolated
Severe. 33 Numerous Thunderstorms. Heavy rain.
10.29.08.2023 50 Scattered Thunderstorms. Few Severe.
Isolated Tornadoes. 35 Numerous Thunderstorms. Heavy rain.
13.29.08.2023 53 Numerous Thunderstorms. Scattered
Tornadoes. 40 Very Unstable. Thunderstorms Very
Likely. Very heavy rain.
16.29.08.2023 52
Scattered Numerous Thunderstorms.
Few Scattered Severe. Isolated
Tornadoes.
41 Extremely Unstable. 100% Chance of
Thunderstorms. Very heavy rain.
19.29.08.2023 48 Scattered Thunderstorms/Isolated
Severe. 37 Very Unstable. Thunderstorms Very
Likely. Heavy rain.
22.29.08.2023 47 Scattered Thunderstorms/Isolated
Severe. 37 Very Unstable. Thunderstorms Very
Likely. Heavy rain.
01.30.08.2023 45 Scattered Thunderstorms. 35 Numerous Thunderstorms. Heavy rain.
As follows from Table 1, during the studied period of time, an unstable atmosphere was generally observed
over Tbilisi. The TT index value varied from 45 (Scattered Thunderstorms.) to 53 (Numerous Thunderstorms.
Scattered Tornadoes.), and the K index - from 33 (Numerous Thunderstorms. Heavy rain.) to 41 (Extremely
Unstable. 100% Chance of Thunderstorms. Very heavy rain.). It should be noted that an unstable atmosphere was
also observed over the territory of western Georgia.
Accordingly, during the indicated period of time, thunderstorms with heavy precipitation were observed over
various parts of the territory of Georgia (including Tbilisi).
29.08.2023, 22.00 hour 29.08.2023, 22.30 hour Scale
Fig. 1. An example of the distribution of lightning discharges over the territory of Georgia on August 29, 2023 at 22.00 and 22.30 hours.
In Fig. 1 an example of the distribution of lightning discharges over the territory of Georgia (including
Tbilisi) on August 29, 2023 at 22.00 and 22.30 hours.
On this day, precipitation was observed almost throughout the entire territory of Georgia.

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Fig. 2. Distribution of daily sum of atmospheric precipitations on the territory of Georgia at August 29, 2023.
In Fig. 2 satellite data about distribution of daily sum of atmospheric precipitations on the territory of Georgia
at August 29, 2023 is presented.
According to the data of the Hydrometeorology Laboratory of TSU (H/S Svanidze), the amount of
precipitation yesterday is equal to 104.4 mm; Hydrometeorology Observatory of National Environmental Agency -
113 mm; satellite data – 45 mm (averaging per 100 km²).
The rain started at approximately 20:00 Tbilisi time and lasted for three hours. As a result of the rain on
August 29, 2023, streets, underground passages, cars, including public transport, were flooded, power lines were
damaged, trees were knocked down, and landslide processes intensified in different parts of Tbilisi. Roofs leaked in
some apartment buildings. In addition, water leaked into the Tbilisi International Airport building and metro
tunnels (Fig. 3).
Fig. 3. An example of flooding of one of the streets of the city of Tbilisi during heavy rain on August 29, 2023
[https://netgazeti.ge/news/685793/].
Note, that in Tbilisi according to meteorological stations precipitation of more than 100 mm per day from
1901 to 2020 only 5 times was observed [5,12]: May 11, 1940 (109.2 mm); June 17, 1948 (125.6 mm); August 16,
1955 (147.2 mm, max in the last 120 years); June 8, 1972 (130.1 mm); June 30, 1997 (117.7 mm).
On June 13, 2015 (Akhaldaba landslide), according to the weather station, the daily precipitation amounted to
49.3 mm. However, according to meteorological radar data, the amount of precipitation over the center of the top
of the landslide from 21.00 to 22.33 hours exceeded 53 mm, and from 21.00 to 23.58 hours – 134 mm [12].

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Conclusion
In the future, we plan to continue similar studies both for Tbilisi and other regions of Georgia, taking into
account climate change.
Acknowledgement
The research is done with the support of "Shota Rustaveli National Scientist Foundation" [Grant number - FR-22-2882].
The authors are grateful to the chief of the atmospheric physics department of M. Nodia Institute of Geophysics A.
Amiranashvili for assistance in the fulfillment of this work.
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https://ggs.openjournals.ge/index.php/GGS/article/view/6959; DOI: https://doi.org/10.48614/ggs2620236959