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

1. WP5.4 Evaluation of extreme events in observational and RCM data Institute of Environmental Research & Sustainable Development National Observatory of Athens, Greece Effie Kostopoulou Christos Giannakopoulos Progress and Plans Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

2. Aim: Evaluate extremes in observational and RCM data for the eastern Mediterranean Deliverable: 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 members De Bilt, 16 May 2008

3. Progress to Date Comparison of an ENSEMBLES Regional Climate Model with observed data in the Balkan Peninsula Presentation 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 Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

4. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Domain of study - Data • RCM data at 25-km horizontal resolution driven by the ERA-40 (ALADIN-Climate Météo-France/ • CNRM & common with the GCM ARPEGE-Climate ) • Station data (53 stations, 8 countries) Variables: Tmax, Tmin Period: 1961-1990 Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

5. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Temporal 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 elevation Cold  low altitudes Max TX: cold biases in high altitudes throughout the year (e.g. Zenica) Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

6. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Temporal evaluation of RCM (TN) 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. observed (blue) modelled (red) Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

7. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Spatial evaluation of RCM (TX) – seasonal Differences North-to-south gradient with positive values in the north and negative in the south of the study region. Winter diff. of up to +3oC Warm bias red: +ve blue: -ve Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

8. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Spatial evaluation of RCM (TN) - seasonal Differences Winter & autumn tendency of the model to underestimate TN (-ve diff) Summer –ve diff mainly in Romanian stations red: +ve blue: -ve Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

9. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Assessment 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 members De Bilt, 16 May 2008

10. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Assessment 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 spells • particularly for island stations located around the Aegean Sea.

11. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Assessment of RCM performance in determining climate extremes Analysis of percentile-based indices (Tx90) – TRENDS Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

12. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Assessment of RCM performance in determining climate extremes Analysis of percentile-based indices (Tn10) - TRENDS Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

13. Regional Climate Model Temperature Simulations Compared with Observed Station Data over the Balkan Peninsula Conclusions 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 model’s 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 members De Bilt, 16 May 2008

14. 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: Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

15. Extremes Indices

16. Work in Progress • Three 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 • cdd Progress meeting for ENSEMBLES-WP5.4 members De Bilt, 16 May 2008

17. C4I CNRM KNMI winter spring summer autumn Differences btwn model – gridded observed TxQ90

18. C4I CNRM KNMI winter spring summer autumn Differences btwn model – gridded observed TnQ10

19. C4I CNRM KNMI winter spring summer autumn Differences btwn model – gridded observed pq95

20. C4I CNRM KNMI winter spring summer autumn Differences btwn model – gridded observed px5d

21. Work Planned NOA 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 model is planned to be 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 members De Bilt, 16 May 2008