Progress meeting for ENSEMBLESWP5'4 members

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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
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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
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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
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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
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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.
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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
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 members De
Bilt, 16 May 2008
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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
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Extremes Indices
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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
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Differences btwn model gridded observed
TxQ90
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Differences btwn model gridded observed
TnQ10
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Differences btwn model gridded observed
pq95
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Differences btwn model gridded observed
px5d
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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