Flash flood · Western Black Sea, Türkiye
The flood that tore through Bozkurt
On 11 August 2021 the small river that runs through Bozkurt, on the Black Sea coast of Kastamonu, rose within hours into a torrent carrying mud, logs and cars. It brought down bridges and swept away apartment blocks built along its banks. Across Kastamonu, Sinop and Bartın 82 people died, most of them in Bozkurt, in Türkiye's deadliest flood in decades.
10–11 August 2021 · Kastamonu, Bartın and Sinop, Türkiye · ERA5
198mm
Rain at Küre, 11 Aug
The highest station total that day; up to 400 mm a day was estimated in the Bozkurt and Ayancık valleys.S1
23mm
ERA5 at Bozkurt, 11 Aug
The Lab's grid point nearest the town: a fifth of what Bozkurt's own station measured.
What happened
Rain began over the western Black Sea coast on 10 August and grew heavier through the night. On 11 August thunderstorms stood over the forested mountains behind the coast, between Bartın and Sinop, for hours. Their water ran off steep, narrow valleys towards the sea. At Bozkurt the Ezine river rose so fast that people had minutes to escape; buildings on its banks collapsed and floating timber piled up against the bridges, raising the water further.N1S1
The same storms flooded Ayancık in Sinop and villages across the three provinces. About 2,400 people were evacuated, many by helicopter and boat.N1
What the stations measured
The Turkish State Meteorological Service's stations measured more than 100 mm in a day across the region, above the rainfall expected once in a hundred years there. In the narrow valleys the survey estimated up to 400 mm a day.S1
| Station | mm |
|---|---|
| Küre | 198 |
| Pınarbaşı | 167 |
| Azdavay | 145 |
| İnebolu | 123 |
| Abana | 122 |
| Bozkurt | 117 |
| ERA5 at Bozkurt | 23 |
1/5
ERA5's rain at its grid point over Bozkurt on 11 August, against the town's own station. A 28 km grid cell spreads a thunderstorm's rain over mountains and sea, and the reanalysis model makes less of it than falls.
The rain on the Lab's maps
Even smoothed, the pattern is clear: on both days the rain is concentrated on the coast and the mountain slopes facing the sea, where moist northerly air was forced to rise.
Warm sea, moist air
Flash floods of this kind need air full of water and something to lift it. In August 2021 the Black Sea was very warm after a hot summer, and a weak low aloft over the region kept the air unstable. Northerly winds carried the moist marine air against the coastal mountains, where it rose into thunderstorms that renewed themselves over the same valleys.
The ERA5 sounding over Bozkurt on the morning of 11 August shows the result: temperature and dew point almost together from the ground to above 400 hPa, a column saturated with water.
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References
News
- N1Bianet. Black Sea floods: death toll rises to 82 with 32 still missing. August 2021.The death toll by province, the evacuations and the scene in Bozkurt.
Studies and guidelines
- S1İstanbul University–Cerrahpaşa (2021). Ağustos 2021 Batı Karadeniz sel felaketi nedeniyle Bozkurt ve Ayancık ilçelerinde oluşan hasarların değerlendirilmesi. Damage assessment of the August 2021 western Black Sea flood (in Turkish).Station rain totals, the return period and the damage in Bozkurt and Ayancık.