Factors Contributing to the Summer 2003 European Heatwave Emily Black, Mike Blackburn, Giles Harrison, Brian Hoskins and John Methven CGAM and Department.

Factors Contributing to the Summer 2003 European Heatwave

Emily Black, Mike Blackburn, Giles Harrison, Brian Hoskins and John Methven

CGAM and Department of Meteorology,

The University of Reading, U.K.

Weather, 59(8), 217-223 (August 2004, special issue)

Summer 2003

• Record European temperature anomalies

• Over 14,000 excess deaths in France alone

• Widespread wild fires

• Reduced crop yields

• Reduced river discharges

• Power generation restrictions (cooling water)

• Increased melting of Alpine glaciers

• A taste of future conditions?

2003 Surface Air Temperature

ECMWF Analyses (ERA-40 climatology)

Streamfunction anomalies

850hPa

• European anticyclonic anomaly

• Low pressure west of UK

• Relatively stationary pattern

May

AugustJuly

June

106 m2s-1ECMWF Analyses (ERA-40 climatology)

Monthly anomalies - NOAA satellite observations

May June

July August

Wm-2

Outgoing Longwave Radiation (OLR)

Sea Surface Temperature anomalies

• Response to radiative anomalies?

degC

Air Parcel Trajectories

• Trajectories arriving at 500m over Paris, 6-12 August

• Anticyclonic descent

• Importance of local energy budget in determining temperatures

Colour: arrival date (red to blue)

ECMWF Analyses

θv profiles : Paris, 6-12 August

ECMWF Analyses

• Deep daytime boundary layer (18UTC, red)

• Shallow nocturnal surface layer (06UTC, black)

Regional Energy Budget: anomalies

• Surface drying amplified radiative forcing of surface temperature

ECMWF 0-24 hour forecast data: 0-20°E; 42.5-52.5°N land only

Reading Observations: August

Upward ground heat-flux: 10Wm-2 heats 100m layer at ~0.3Khr-1

Reading Observations: 10th August

• Upward ground heat flux slows nocturnal cooling

• Elevated nocturnal temperatures prolong heat stress, important for human mortality

Ensemble Modelling

Unified Model (HadAM3)

Control ensemble forced by Reynolds/NCEP SST preceding decades

2003 global SSTs, or omitting specific regions

- See poster by Emily Black and Rowan Sutton -

• European warmth captured by 2003 global SST ensemble

• Evidence for forcing from Indian Ocean SST

• Opposing effect of Mediterranean SST?

Schaer et al (2004), Nature

Model data from PRUDENCE EU project

Regional modelling over Europe up to present-day and for late 21st century.

Driven by high-resolution GCM climate-change expts

Variability of Swiss summer temperature and

precipitation anomalies

1864-2003

1961-19902071-2100

Observations

Model

Schaer et al (2004), Nature

Model data from PRUDENCE EU project

Variability of Swiss summer temperature and

precipitation anomalies

By the end of this century, under a high-emissions scenario, summer 2003 European temperatures could be seen as “normal”!

1864-2003

1961-19902071-2100

Observations

Model

- A recent climatology -

2003 anomaly relative to the 1961-90 average is large

Tem

per

atur

e (d

egC

)

Year

Central England temperature (CET)Summer (JJA) 1860-2003

- An evolving climatology -

Using an evolving climatology reduces the 2003 anomaly:

2003:

1.4 vs. 2.4 * Std.Dvn.

8% vs. 0.9% probability

13 vs. 110 year return period

(gaussian assumption)

Tem

per

atur

e (d

egC

)

Year

Central England temperature (CET)Summer (JJA) 1860-2003

Black: 1860-2002 average (very close to 1961-90)Red: evolving climatology – smoothed spline

Summer CET probabilities

2003

Temperature (degC)

Pro

bab

ility

den

sity

Red: PDF relative to fixed climatologyPale: PDF relative to evolving climatology at 2003

Ranking of extremes

• 2003 was 12th warmest (not 3rd) relative to the evolving climatology

coolest Rank warmest

Tem

per

atur

e (d

egC

)Central England summer temperature (JJA)

2003

Relative to fixed climate

Relative to evolving climate

Evolving Climatology - Issues

• Sensitive parameters and deductions:

• Partitioning into inter-annual and forced variability

• Attribution: robust estimation; confidence measures (Stott et al, 2004)

• Increasing importance as climate change accelerates

– Magnitude of anomalies

– Return periods

– Ranking of extreme events

– PDFs

Conclusions

• Anticyclonic anomaly dominated:

• Stationary pattern in European – Atlantic sector

• Evidence for remote influence

• Non-stationary climatology - implications

• A taste of things to come?

– Weak advection; local energy budget dominates

– Soil drying a positive feedback on surface temperature

– Upward ground heat flux limits nocturnal cooling