Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends?...

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Topics: Major floods 1993- 2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993 and in Jan 1995 again. Meteorological and climatological aspects of river flood assessment in Central Europe Bruno Rudolf (et al.), Global Precipitation Climatology Center, Deutscher Wetterdienst, Offenbach am Main

Transcript of Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends?...

Page 1: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Topics:

• Major floods 1993-2002• Precipitation patterns• Observational problem• Flood assessment• Trends?

Example:

Century flood of Rhine and Mosel in Dec 1993 and in Jan 1995 again.

This photo was published on New York Times cover page.

Meteorological and climatological aspects of river flood

assessment in Central Europe Bruno Rudolf (et al.), Global Precipitation Climatology Center,

Deutscher Wetterdienst, Offenbach am Main

Page 2: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Selected major floods in Central Europe during the past ten years:

1993 Sep 23/24 heavy flash floods in the southern Alps (Brigs!) and nothern Italy

1993 December Rhine and Mosel river flood, Germany

1995 January Rhine and Mosel river flood, Germany

1997 July Odra river flood, Poland and Germany

1999 May Danube river, Lake Constance, Austria, Germany

2000 Sep-Nov Persistent river floods in wide-spread regions of western and southern Europe

2001 July Vistula river flood, Poland

2002 August Danube river flood, Germany and Austria Elbe river flood, Czech Republic and Germany

2002 Sep 08/09 heavy flash floods, Southern France (Rhone)

2003 January floods of many tributaries of Rhine and Elbe

Page 3: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Century flood of Rhine and Mosel in December 1993

GPCC analysis of monthly precipitationbased on data received via GTS

The situation is similar to the one of January 1995, when a 2nd century flood of Rhine and Mosel occured.

Spatial extent ~ 1000 kmrelevant period ~ 1 monthrainfall and snow melt

PrecipitationDec. 1993

PrecipitationDecember normal

Anomaly (mm)Dec. 1993

% of normalDec. 1993

Page 4: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Wide-spread floodings in Europe, Autumn 2000

Map: Precipitation for the period Sep-Nov 2002 (dark green > 600mm)

Diagrams: Daily precipitation as observed at selected stations(scale 0 – 125 mm/d)

Page 5: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Floods of Danube and Lake Constance in May 1999 Red bars: Daily precipitation at Zugspitzeblack lines: Snow depth at Zugspitze and Wendelstein

Snow melt (1000-3000m msl) and a short-time extreme rainfall event

Page 6: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Odra Flood in July 1997 and Vistula flood in July 2001

Monthly precipitation totals in mm

spatial extent ~ 300 km relevant period < 1 week

Vb Wetterlage + orographical effects => intense rainfall

spatial extent ~ 100 km relevant period < 1 week

Page 7: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Elbe Flood, August 2002

Meteorological situation on 11 August, 500 HPa and surface

Page 8: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Elbe Flood, August 2002

Storm track of the cyclone (location of occlusion

Page 9: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Floods of Danube and Elbe, August 2002

Precipitation totals in mm for the two episodes

6 - 8 August 2002 and 10 - 13 August 2002 (6-6 UTC)

Page 10: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Floods of Danube and Elbe, August 2002

Time series of monthly precipitation (mm) for August

Highest observed values for Zinnwald-Georgenfeld (Erzgebirge):

Monthly precipitation total = 470 mm, anomaly = 456 %Maximum daily precipitation = 312 mm, occurence = 1 per 150 yearsmaximum 24h precipitation = 357 mm Maximum hourly precipitation = 30.5 mm

Page 11: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Elbe Flood, August 2002 Hourly precipitation at Dresden and Zinnwald on 12 to 13 August 2002

Page 12: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

The Elbe Flood, August 2002 - meteorological causes:

Meteorological factors leading to the extreme conditions:

• Convergence, large-scale strong and quasi-stationary lifting

• Very high atmospheric liquid water content

• Embedded convective cells

• Additional orographically forced lifting

• Saturated deep soil and already high river levels

Fractions of the different precipitation mechanisms:

• Stratiform precipitation: 2 parts

• Convective precipitation: 1 part

• Orographic amplification: duplication of the quantities

Page 13: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Precipitation accumulated for the period 10 Aug 06 UTC - 13 Aug 06 UTC

GME forecast LM forecast Observation

The Elbe Flood, August 2002

Page 14: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Extreme Flash Flood in the lower Rhone area, 8 and 9 Sept. 2002

The largest reported daily precipitation is 650 mm observed on 8 Sept. at Anduze.

Other precipitation reports of Meteo France:

1 Mont-Aigoual 114.2 mm 8 Sep

2 Générargues 588.5 mm 8-9 Sep

3 La Rouvière 541.0 mm 8-9 Sep

4 Gajan 550.0 mm 8-9 Sep

5 Nimes-Courbessac 169.6 mm 8-9 Sep

6 Vaison La Romaine 103.5 mm 8-9 Sep

7 Orange 314.0 mm 8-9 Sep

8 Chateauneuf du Pape 390.5 mm 8-9 Sep

9 Carpentras 154.8 mm 8-9 Sep

Page 15: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Heavy Flash Floods in the Rhone delta, 8 and 9 Sep. 2002

A first precipitation analysis of the GPCC for the period 7 Sep. 18 UTC - 10 Sep. 6 UTC

was based on synoptical reports received from the GTS.

The highest 54h total from GTS: 170.2 mm

The extreme values observed at national stations have not been available on GTS.

Page 16: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Maximum river levels of Elbe in Dresden since 1640

Most of the Elbe floods occured in winter or spring.

Typical summer floods happened in 1890 and 2002.

A statistical evaluation of the river levels is problematic:

• Extreme floods of a specific river are rare.

• The runoff is influenced by human inventions.

• The causes of extreme floods are different.

Page 17: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Types of floods related to meteorological conditions(in particular for Central Europe)

Flash floods (mostly summer) Heavy thunderstorms, squall lines

River floodings (summer, autumn) Regionally large rain quantities, synoptic regime (Vb), orography

River floodings (winter, spring) Largescale rainfall and/or snow melt

River floodings (winter) Frost: ice barriers blocking the river flow

Continent wide floodings Persistent large scale cyclonic and humid synoptic regime, convergent stream flow

Page 18: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Conclusions

• NWP models mostly well simulate the meso-scale atmospheric structures. However, they do not forecast extreme precipitation quantities and the location of the affected region with sufficient accuracy. Thus, the models may fail in forecasting individual flash floods, but they can base conditional warnings on the probability of rainstorms for a certain region.

• Forecast of large river floods requires not only prediction of precipitation and snow melt but also of the river level, the progressing of the flood wave, based on monitoring of the river level, analysis of the observed precipitation and soil moisture conditions.

• Floods represent individual extrem events stamped by various interacting processes. Any interpretation of the frequency of flood events is problematic due to the different meteorological causes and human influence (river bed regulation, discharge management).

• Classification of precipitation episodes with respect of the areal coverage and duration is a suitable basis for statistical assessment of the frequency of relevant episodes and extreme events. => A suffient data base is required.

Page 19: Topics: Major floods 1993-2002 Precipitation patterns Observational problem Flood assessment Trends? Example: Century flood of Rhine and Mosel in Dec 1993.

Additional material:

Bruno Rudolf und Jörg Rapp (2003): Das Jahrhunderthochwasser der Elbe: Synoptische Wetterentwicklung und klimatologische Aspekte. In Klimastatusbericht 2002 des DWD, Offenbach, erscheint Juni 2003.

Bruno Rudolf and Jörg Rapp (2003): The Century Flood of the River Elbe in August 2002: Synoptic Weather Development and Climatological Aspects. To be published by DWD in July 2003.

Bruno Rudolf und Clemens Simmer (2002): Niederschlag, Starkregen und Hochwasser. In Wiss. Mitteilungen aus dem Inst. für Meteorologie der Univ. Leipzig, Sonderheft zum Jahr der Geowissenschaften, S. 28-43.