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), (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 10 6 m 2 s -1 ECMWF Analyses (ERA-40 climatology)

Outgoing Longwave Radiation (OLR) JJA 2003 anomaly Wm -2 NOAA satellite observations

Monthly anomalies - NOAA satellite observations May June JulyAugust 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

θ v profiles : Paris, 6-12 August ECMWF Analyses Deep daytime boundary layer (18 UTC, red) Shallow nocturnal surface layer (06 UTC, black)

Regional Energy Budget: anomalies Surface drying amplified radiative forcing of surface temperature ECMWF 0-24 hour forecast data: 0-20°E; °N land only

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

Reading Observations: 10 th 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?

Climate Change Context Regional modelling for 21 st century Static or evolving climatologies? Attribution of this event to global warming?

Schaer et al (2004), Nature Model data from PRUDENCE EU project Regional modelling over Europe up to present-day and for late 21 st century. Driven by high-resolution GCM climate-change expts Variability of Swiss summer temperature and precipitation anomalies 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! Observations Model

- A recent climatology anomaly relative to the average is large Temperature (degC) Year Central England temperature (CET) Summer (JJA)

- 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) Temperature (degC) Year Central England temperature (CET) Summer (JJA) Black: average (very close to ) Red: evolving climatology – smoothed spline

Summer CET probabilities 2003 Temperature (degC) Probability density Red: PDF relative to fixed climatology Pale: PDF relative to evolving climatology at 2003

Ranking of extremes 2003 was 12 th warmest (not 3 rd ) relative to the evolving climatology coolest Rank warmest Temperature (degC) 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