Extremes in climate models Jean Palutikof Climatic Research Unit University of East Anglia Norwich, UK Workshop on Development of Scenarios of Climate Variability and Extremes Victoria, BC

1.Temperature extremes References: B.B. Brabson, D. H. Lister, J. P. Palutikof, P. D. Jones: Rapid rise of extreme temperatures in the 21st century. Submitted to Geophysical Research Letters Brabson, B.B. and Palutikof, J.P., 2002: The Evolution of Extreme Temperatures in the Central England Temperature Record. Geophysical Research Letters, 29 (24), /2002GL

For observed Central England temperatures

GPD (peak-over-threshold) Three parameters:  scale  shape  selected threshold CDF: Three classes defined by the value of   > 0Long-tailed case  = 0Exponential tail  < 0Short-tailed case, finite endpoint Return-period temperature:

GPD analysis of observed historical daily CET Analyses carried out on January/February warm and cold tails, and July/August hot and cool tails POT thresholds selected at each time step to include 5% values; separation distance of 4 days to ensure independence Based on 20-year overlapping periods, and looking at – the mean, , of all values, –1SD above and below the mean –the 10-year return period temperature, T 10

Year Temperature (°C) Jan/Feb a ± ± ± ± ± Year July/Aug b Warm T 10 Mean + 1 S.D. Mean Mean - 1 S.D. Cool T ± ± ± ± ± 0.17 Temperature (°C)

Fraction Winter Fractions by Type Anticyclonic Easterly Southerly Westerly a Avg. Temp. (°C) Winter Temperature by Type Anticyclonic Easterly Southerly Westerly b Fraction Winter Extreme Fractions Anticyclonic Easterly Westerly Southerly c S.D. (°C) Winter Temperature S.D. Anticyclonic Easterly d

For future modelled Central England temperatures

Inter-experiment comparison of temperature extremes Annual extremes for: –January/February Highest TMIN (blue) Lowest TMIN (black) –July/August Highest TMAX (red) Lowest TMAX (green) Hadley Centre models: –HadCM3 A2 –HadCM3 B2 –HadCM2 (IS92a gg) For the Eastern England gridbox CET

Annual maxima/minima for SE England

Three parameters:  position  scale  shape CDF: Three classes defined by the value of   > 0Long-tailed case Fréchet  = 0Exponential tail Gumbel  < 0Short-tailed case, finite end, Weibull Return-period temperature: GEV distribution (annual maxima)

GEV analysis of modelled future daily ‘CET’ For winter TMIN and summer TMAX The Eastern England grid boxes The HadCM3 A2 experiment Based on 20-year overlapping periods, showing: T10 (warm tail)  (warm tail) the mean, smoothed with a 25-term filter  (cold tail) T10 (cold tail)

Moment-based contributions to HadCM3(A2): winter tmin (black; summer tmax (red)

Number of spells (Eastern England grid box)

Tmax as a function of soil moisture hot tail (red), mean (black), cold tail (blue)

Summary The GCMs predict a rapid rise in temperature over southern England Summer hot extremes rise much faster than the corresponding mean Soil moisture in HadCM3 provides the link between slowly rising means and rapidly rising extremes

2.High wind speeds and windstorm C. Hanson et al., Proc. ‘Wind Effects on Trees, Karlsruhe, 2003 Hanson, C.E., and Palutikof, J.P., 2004: Variations in a UK cyclone climatology constructed from a group of nested climate models. Submitted to Geophysical Research Letters.

North Atlantic: Intensity Changes AB CD Central Pressure (hPa) Deepening Rate (hPa/12hr)

North Atlantic: Spatial Changes

UK Region: Intensity Changes

UK Region: Temporal Changes HadRM3H baseline period ( ) HadRM3H A2a experiment ( ) HadRM3H B2a experiment ( ) HadAM3H baseline period ( ) HadAM3H A2a experiment ( ) HadAM3H B2a experiment ( ) ≤1000hPa≤970hPa

Summary Analysis of North Atlantic and UK cyclone activity in HadAM3H and HadRM3H has revealed no significant change in activity – frequency or intensity. HadAM3H indicates an increase in weaker events over south-east England. Potential for change in seasonality of the more intense events (HadRM3H). In general, the results are inconclusive.

A different approach allows identification of storm tracks Work by the University of Koeln for the MICE project

HADCM3: Identification of Cyclones for the European Sector Track density Winter (=ONDJFM) A2a – CON_aCON_a Extreme cyclones > 99th percentile Unit: Systems / Grid Unit / Winter Contour interval 0.1 MICE – Work Progress of Partner 4 (UKOELN): U. Ulbrich, G. Leckebusch MICE Project Meeting, Athens,

HADCM3: Identification of Cyclones for the European Sector Core Pressure Winter (=ONDJFM) A2a – CON_aCON_a Extreme cyclones > 95th percentile Unit: hPa Contour interval 2.0 MICE – Work Progress of Partner 4 (UKOELN): U. Ulbrich, G. Leckebusch MICE Project Meeting, Athens,

HadRM3: A2a-CON, Climate Signal Wmax, 95 Percentil CON_aA2a – CON_a MICE Project Meeting, Athens, MICE – Work Progress of Partner 4 (UKOELN): U. Ulbrich, G. Leckebusch

HADCM3: Identification of Cyclones for the European Sector Summary:  all systems: track density reduction, especially northern Europe (above the Norwegian Sea, Scandinavia)  extreme (> 95th or > 99th percentile) systems: track density reduction: Northern Europe track density increase: South of 60N, Western Europe deepening of extreme cyclones  Scenarios A2 and B2 differ mainly with regard to extreme systems  A2: Increase of extreme systems in western central Europe MICE – Work Progress of Partner 4 (UKOELN): U. Ulbrich, G. Leckebusch MICE Project Meeting, Athens,

3.Rainfall extremes Some results from the EU-funded MICE and PRUDENCE projects Modelling the impacts of climate extremes Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects

How much can we believe what the models tell us? A comparison for an RCM gridbox with many rain gauges

Southern England – 24 rain gauges in the central gridbox

Number of wet and dry days

Number of days with high rainfall

What do the models tell us?

Precipitation indices: maximum length of dry spell per year ( minus ) A2a scenario A2a B2a A2a: –Longer by days in centre and south east –10 days shorter over northern Europe B2a: –Smaller changes than A2a –wetter Eastern Med.

Precipitation indices: start of drought ( minus ) A2a scenario A2a B2a A2a: –5-10 days earlier in future –No change over much of northern Europe B2a: –3-5 days earlier in future

Precipitation indices: end of drought ( minus ) A2a scenario A2a: –Generally no change or slightly earlier end in future –later over centre and south east B2a: –Very similar to A2a

Precipitation indices: max. 5-day running total ( minus ) A2a scenario A2a: –Lower by mm in future, particularly in west –Wetter in centre and Adriatic B2a: –Smaller changes than A2a –Clearly wetter in Italy

Precipitation indices: summary Summer Mediterranean droughts likely to start earlier under A2a, particularly in south east Mediterranean Summer droughts in northern Europe likely to be slightly shorter under A2a Western and eastern Mediterranean drier in winter under A2a, Adriatic and central Italy wetter Under B2a all A2a changes reduced, Italy wetter

What can climate models tell us about extremes? Used appropriately, model data can be applied without intervening statistical downscaling to explore extremes, thus avoiding such issues as preservation of relationships in spatial and temporal fields and whether or not all contributing forcing factors have been taken into account Processing with techniques such as: Extreme value analysis Storm tracking algorithms can yield valuable information