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