SST influence on extreme precipitation in SST influence on extreme precipitation in RomaniaRomania

Roxana Bojariu, Ecaterina Ion-Bordei, Filippo Giorgi, Sara Rauscher and Xunqiang Bi

MotivationsPhysical mechanisms?

Radar – 23 martie 2007 Flash flood episode of Flash flood episode of 22-23 March 2007:22-23 March 2007:•38 villages affected 38 villages affected •150 houses damaged150 houses damaged•28 persons evacuated28 persons evacuated•800 de ha of agricultural terrain damaged800 de ha of agricultural terrain damaged•21 km of roads21 km of roadsdamageddamaged

Flash flood episode of Flash flood episode of 22-23 October 2007:22-23 October 2007:•100 villages affected100 villages affected

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1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81 86 91 96

-2.5

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-1.5

-1

-0.5

0

0.5

1

1.5

2

1901

1912

1923

1934

1945

1956

1967

1978

1989

CRU filtered P

Ensemble meanfiltered P

DataData Daily Precipitation from 104 Romanian stations (1961-2001)

(Administratia Nationala de Meteorologie, Romania); Sea surface temperature (SST) – ERA40 (1961-2001) (ECMWF); Mediterranean Cyclone Catalog :( Ecaterina Ion-Bordei). numerical experiments with a regional climate model - RegCM 3,

version 3 of RegCM (horizontal grid interval 30 km) – with the help of Filippo Giorgi, Sara Rauscher and Xunqiang Bi .

MetodologyMetodology Indices of extreme precipitation are computed from daily data for

winter: R95 (R98) - daily amounts equal or above the 95% percentile;

Canonical correlation analysis applied to the pairs total precipitation and SST, R95 and SST and R98 and SST;

Composites maps for 9 winter cases of Mediterranean cyclones crossing Romanian territory;

CCA analysis of observed extreme precipitation (PR95) and SSTDecember to February R=0.73

25% 17 %

Time evolution of 1st CCA mode

R=0.73R=0.73

CCA analysis of observed extreme precipitation (PR95) and SSTMarch to May R=0.73

9 % 8 %

Temel Oguz, Joachim W. Dippner, Zerefsan Kaymaz, 2006: Climatic regulation of the Black Sea hydro-meteorological and ecological properties at interannual-to-decadal time scales. Journal of Marine Systems 60, 235–254.

+2

Interdecadal signal

Numerical experiments: +2Exp minus CtrlExp ( 9 winter cases composites)

a) b)

Total column precipitable water Sea level pressure

Numerical experiments: +2Exp minus CtrlExp ( 9 winter cases composites of geopotential heights)

Z850 Z500

Observed and simulated precipitation composites - 9 winter cases

b)Ctrl Expa)Obs.

c) +2 Exp

Observed and simulated composites for precipitation

Observed precipitation composite (mm/day) 1961-1979 minus 1980-1995

Simulated composites of 9 winter cases (mm/day)+2 Exp minus Ctrl Exp

ConclusionsConclusions

1. Extreme precipitation variability in Romania has a strong interdecadal component.

2. On regional scale, Black Sea SSTs seem to modulate precipitation and extreme precipitation, especially in the cold season

3. The cold season signal is robust and may be used in predictive methodologies and in projecting regional changes in precipitation under future climate conditions.

4. Further investigation is needed using both observed data and results from regional climate models to find other regional mechanisms (e.g. for the warm season).