WP5.4 Evaluation of extreme events in observational and RCM data

WP5.4 Evaluation of extreme events in observational and RCM data

Institute of Environmental Research & Sustainable Development National Observatory of Athens, Greece

Effie KostopoulouChristos Giannakopoulos

Progress and PlansProgress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Aim:

Evaluate extremes in observational and RCM data for the eastern MediterraneanDeliverable:

D5.33: Scientific paper on the ability of different RCMs to represent extremes in the eastern Mediterranean (Month 60)

Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Progress to DateComparison of an ENSEMBLES Regional Climate Model with observed data in the Balkan PeninsulaPresentation of results during the annual EGU 2008 meeting: E. Kostopoulou, K. Tolika, G. Tegoulias, C. Anagnostopoulou, P. Maheras and C. Giannakopoulos: Regional climate model temperature simulations compared with observed station data over the Balkan Peninsula

Collaborative study between National Observatory of Athens and Aristotle University of Thessaloniki (RT4/RT5)

Submission of journal paper:

E. Kostopoulou, K. Tolika, I. Tegoulias, C. Giannakopoulos, S. Somot, C. Anagnostopoulou and P. Maheras: Evaluation of a Regional Climate Model using in-situ temperature observations over the Balkan Peninsula


Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaRCM data at 25-km horizontal resolution driven by the ERA-40 (ALADIN-Climate Mto-France/CNRM & common with the GCM ARPEGE-Climate )

Station data (53 stations, 8 countries)Domain of study - DataVariables: Tmax, TminPeriod: 1961-1990Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaTemporal evaluation of RCM (TX)

Average mean (middle curves), absolute max (upper) and min (lower) TX for each calendar-day during the period of study, for the observed (blue) and modelled (red) temperatures.

Mean, min TX: biases mainly during the cold season: Warm higher elevationCold low altitudes

Max TX: cold biases in high altitudes throughout the year (e.g. Zenica)Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaTemporal evaluation of RCM (TN)

observed (blue) modelled (red)More pronounced biases.

Mean TN: better results for low-altitude stations.

High altitudes: overestimated max/min TN.

E.g. the overestimation is such that the mean model TN is as high as the highest station TN (local effects ?)

Low altitudes: underestimated max/min TN. Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaSpatial evaluation of RCM (TX) seasonal Differences

red: +veblue: -veNorth-to-south gradient with positive values in the north and negative in the south of the study region.

Winter diff. of up to +3oCWarm biasProgress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaSpatial evaluation of RCM (TN) - seasonal Differences

red: +veblue: -veWinter & autumn tendency of the model to underestimate TN (-ve diff)

Summer ve diff mainly in Romanian stationsProgress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaAssessment of RCM performance in determining climate extremes Analysis of warm and cold spells

The model generally overestimates the occurrence both warm and cold spells .Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaAssessment of RCM performance in determining climate extremes Analysis of warm and cold spells (% of coincidence)

The percentage of coincidence in both cold and warm spells is relatively high for the transitional seasons.

Winter: better for warm spells Summer: better for cold spellsparticularly for island stations located around the Aegean Sea.

Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaAssessment of RCM performance in determining climate extremesAnalysis of percentile-based indices (Tx90) TRENDS


Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaAssessment of RCM performance in determining climate extremesAnalysis of percentile-based indices (Tn10) - TRENDS


Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan PeninsulaConclusions

The model accurately described the seasonal cycle and simulated the spatial distribution of TX and TN. Altogether, the model performed better for TX than TN and better for the transitional seasons of the year. The model performed better at low-altitude stations along the coasts, highlighting the constraints of the topographic forcing in the simulations.

Assessing the performance of the model to determine extremes, the model results did not seem to be very sensitive in detecting particular events of warm/cold spells. This could be attributed to the poor behaviour in terms of time chronology, as it is expected for the RCM to lose their time chronology in a region that lies so far from the models western boundary. In contrast the model exhibited a remarkable ability to reproduce the seasonal trends of Tx90 and Tn10. Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

Work in Progress

NOA will perform an evaluation of ENSEMBLES RCM data against observational datasets from Greek stations and against gridded observational data available from WP5.1 for the eastern Mediterranean.

Comparison of these datasets will be made using selected indices of extremes for temperature and precipitation.

The main focus will be to identify strengths and weaknesses in RCM data in their ability to represent extremes. Some examples of indices of extremes that can be used for the case study region of the Mediterranean are shown in the following slide:


Extremes Indices

TemperatureTmax 90th percentile Tmin 10th percentile Heat Wave DurationNumber of summer days per year (TX > 25oC)Number of tropical nights per year (TN > 20oC)Number of frost days (TN < 0oC)Number of very cold nights per year (TN < -5oC)

Precipitation95th percentile of rainday amountsGreatest 5-day total rainfallTotal No. of days per year with precip >= 20mmMaximum length of dry spell in a year (days)Maximum length of wet spell in a year (days)

Work in ProgressThree ENSEMBLES Regional Climate Models are compared to the ENSEMBLES gridded observational dataset

Seven climate extreme indices are obtained from a collaborative study with RT4 (Aristotle University of Thessaloniki)

TxQ90 TnQ10 hwd fd pQ95 px5d cddProgress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

InstituteScenarioDriving GCMModelC4IA2ECHAM5RCA3CNRMA1BARPEGEAladinKNMIA1BECHAM5RACMO

Differences btwn model gridded observedTxQ90

Differences btwn model gridded observedTnQ10

Differences btwn model gridded observedpq95

Differences btwn model gridded observedpx5d

Work PlannedNOA will perform a comprehensive analysis of several indices that represent key aspects of climate extremes.

Using these indices, grid cells that present differences in RCM data with observations will be identified.

Physical explanations for these discrepancies will be researched based on specific topographical features of each location that is probably not possible to be represented in RCMs.

Several RCMs will be compared with the gridded and station data and the ability of each RCM to represent specific extremes will be rated.

A reliability (weighting) factor for each modelis planned tobe quantified specifically for the eastern Mediterranean region.

These weights will be assigned to the different ENSEMBLES RCMs (instead of treating separate simulations as "equally likely") and so their results can be combined into a scenario to assess future climate changes in the eastern Mediterranean. Progress meeting for ENSEMBLES-WP5.4 membersDe Bilt, 16 May 2008

******************Warm and cold spells were detected and compared with those derived from the observational datasets. The spells are defined as sequences of 5, 6, 7, 8, 9 days or longest than 10 days duration with temperatures exceeding the 90th percentile (warm spell), or below the 10th percentile (cold spell) of the temperature distribution. **The coincidence rate of spells for each location was calculated as a percentage based on the number of common spells between the two datasets divided by the number of spells of the station data. Common spells are considered to be those with at least two days in common between the two datasets. **********************

WP5.4 Evaluation of extreme events in observational and RCM data

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