1. Effects of NAO on combined temperature and precipitation winter modes and
snow cover in Mediterranean mountains:
observed relationships and projections for the 21st century
J. Ignacio López-Moreno
nlopez@ipe.csic.es

2. IMPACT OF NAO ON WINTER TEMPERATURE AND PRECIPITATION MODES
AND SNOW COVER IN THE MEDITERRANEAN MOUNTAINS
- Plant and animal phenology
-Tourism
- Natural hazards: avalanches and floods
- Water resources

3. SNOW IN THE MEDITERRANEAN MOUNTAINS
Atlas
Iberian peninsula
Alps and Apenines
Carphatians Lebanon
Turkey

4. CORRELATION OF NAOi WITH WINTER (DJFM) PRECIPITATION AND
TEMPERATURE: 1950-2005
Precipitation
Temperature
Correlation significant
at 95%

5. Objectives
1- To assess the effect of NAO on combined precipitation and temperature and
snow accumulation in the Mediterranean mountains.
2- To assess the capability of GCMs for reproducing the observed relationships.
3- To check if simulated relationships will remain stationary or will change in the
next century due to increasing GHGs concentrations.
Problem: In general snow data is scarce and not available for researchers in most
of the Mediterranean region.

6. Winter modes approach
1- Warm and wet (WW): Tª>60th percentile; Precip>60th percentile
2- Warm and dry (WD): Tª>60th percentile; Precip<40th percentile
3- Cold and wet (CW): Tª<40th percentile; Precip>60th percentile
4- Cold and dry (CD): Tª<40th percentile; Precip<40th percentile
Château d’Oex, Davos, Arosa, Saentis,
1.0
DJFM mean snow accumulation (percentiles)
980 m a.s.l. 980 m a.s.l. 1850m a.s.l. 2500 m a.s.l.
0.8
0.6
0.4
0.2
0.0
WW WD CW CD WW WD CW CD WW WD CW CD WW WD CW CD

7. Winter modes approach
1- Warm and wet (WW): Tª>60th percentile; Precip>60th percentile
2- Warm and dry (WD): Tª>60th percentile; Precip<40th percentile
3- Cold and wet (CW): Tª<40th percentile; Precip>60th percentile
4- Cold and dry (CD): Tª<40th percentile; Precip<40th percentile
Château d’Oex, Davos, Arosa, Saentis,
1.0
DJFM mean snow accumulation (percentiles)
980 m a.s.l. 980 m a.s.l. 1850m a.s.l. 2500 m a.s.l.
100
Château d’Oex, 980 m a.s.l. Saentis, 2500 m a.s.l.
0.8 600
80
Snow depth
Snow depth
60
0.6
400
40 0.4
200
20
0.2
0 0
0 50 100 150 200 250 0 50 100 150 200 250
0.0
Day Day
Warm/Wet Cold/Wet CW CD CW CD
WW WD CW CD WW WD CW CD WW WD WW WD
Warm/Dry Cold/Dry

8. Study area and case studies
6 8
9 14
1 3 7 11 13
2
10
4
12
15
5
1- Cantabrian M. (7) 5- Atlas (84) 9- Dinaric Alps (18) 13- N. Turkey (181)
2- Central S. (10) 6- Alps (113) 10- Pindos (23) 14- Caucasus (85)
3- Pyrenees (22) 7- Apenines (16) 11- Balkan M. (16) 15- Lebanon M. (8)
4- S.Nevada (4) 8- Carpathians (16) 12- Taurus (87)
Data: CRU TS2.1 (50km grid size). Study period: 1950-2005

9. Iberian Peninsula: Pyrenees 3
1
4
López-Moreno and Vicente-Serrano (2007). Atmospheric circulation influence on the interannual variability of snow pack in
the Spanish Pyrenees during the second half of the 20th century. Nordic hydrology 38 (1):38-44.

10. Iberian Peninsula: Pyrenees 3
Teleconnection Snow
Component 1
index accumulation
NAO *-0.38 *-0.39
EA -0.17 0.06
EA/WR -0.24 -0.04
SCA 0.19 0.26
* α <0.05
López-Moreno and Vicente-Serrano (2007). Atmospheric circulation influence on the interannual variability of snow pack in
the Spanish Pyrenees during the second half of the 20th century. Nordic hydrology 38 (1):38-44.

11. Iberian Peninsula: Pyrenees 3
173 of 241 major avalanche events in the
Pyrenees have been observed during winters
dominated by negative NAOi
García et al. (2009) Major avalanches occurrence at regional scale and related atmospheric circulation patterns in the
Eastern Pyrenees. Cold Regions Science and Technology 59 (2009) 106–118

12. Iberian Peninsula 1- Cantabrian M.
3
2- Central S.
3- Pyrenees
4- S.Nevada
2
4
Correlation between winter NAOi(DJFM) and winter precipitation and temperature
1.0
Cantabrian mountains Central System Pyrenees Sierra Nevada
0.8
0.6
Coefficient of correlation
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
Tmn Tmx Tavg Precip
Tmx Tmn Tavg Prec. Tmx Tmx Tavg Prec.
Tmn Tmn Tavg Precip Tmn Tmx Tavg Precip
Tmx Tmn Tavg Prec. Tmn Tmx Tavg Precip
Tmx Tmn Tavg Prec.

13. Iberian Peninsula 1- Cantabrian M.
3
2- Central S.
3- Pyrenees
4- S.Nevada
2
4
WD WW
1.0
NAO 0.8
-2.0
-1.5
Temperature
-1.0 0.6
-0.5 Cantabrian M.
Central System Central S. Pyrenees S. Nevada
0.0
0.5 0.4
1.0
1.5
2.0 0.2
0.0
0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.00.0 0.2 0.4 0.6 0.8 1.0
0.0 0.2 0.4 0.6 0.8 1.0
Precipitation Precipitation Precipitation Precipitation
CD CW
3
Cantabrian mountains Central System Pyrenees Sierra Nevada
2
NAO (DJFM)
1
0
-1
-2
-3
WW WD CW CD WW WD CW CD WW WD CW CD WW WD CW CD
Winter NAOi(DJFM) under different combinations of precipitation and temperature

14. Morocco: Atlas
1.0
Atlas
0.8 1.0
0.6 3
Coefficient of correlation
0.8 Atlas
0.4 NAO 2
-2.0
0.2
Temperature
NAO (DJFM)
-1.5 0.6 1
-1.0
0.0 -0.5
0.0
Atlas
0
0.5
0.4
-0.2 1.0 -1
1.5
-0.4 2.0 0.2 -2
-0.6 -3
0.0 WW WD CW CD
-0.8 0.0 0.2 0.4 0.6 0.8 1.0
Precipitation
-1.0
Tmx Tmn Tavg Prec.
Tmn Tmx Tavg Precip

15. Alps
1.0
Y Data
Alps
0.8
0.6
Coefficient of correlation
1.0
0.4
3
0.2 0.8 Alps
NAO 2
0.0
NAO (DJFM)
Temperature
-2.0 0.6
-1.5 1
-0.2 -1.0 Alps
-0.5
0.4
0
0.0
-0.4 0.5
-1
1.0
1.5 0.2
-0.6 2.0 -2
-0.8 0.0 -3
0.0 0.2 0.4 0.6 0.8 1.0 WW WD CW CD
Precipitation
-1.0
Tmx Tmn Tavg Prec.
Tmn Tmx Tavg Precip

16. Apenines
1.0
Apenines
0.8 1.0
0.6
Coefficient of correlation
3
0.8 Apenines
0.4 NAO
-2.0
2
0.2 -1.5
Temperature
0.6
NAO (DJFM)
-1.0 1
0.0 -0.5
Apenines
0.0 0
-0.2 0.5 0.4
1.0
1.5
-1
-0.4 2.0
0.2 -2
-0.6
-3
-0.8 WW WD CW CD
0.0
-1.0 0.0 0.2 0.4 0.6 0.8 1.0
Tmn Tmx Tavg Prec.
Tmx Tmn Tavg Precip Precipitation

17. 1.0
Dynaric Alps Pindos Balkan M. Carpathian
Balkans 0.8
Carphatian
0.6
Coefficient of correlation
0.4
Dynaric Alps 0.2
Pindos 0.0
-0.2
-0.4
-0.6
-0.8
-1.0
Tmx Tmn Tavg Prec. Tmx Tmn Tavg Prec. Tmx Tmn Tavg Prec. Tmx Tmn TavgPrecip
Tmn Tmx TavgPrecip Tmn Tmx TavgPrecip Tmn Tmx TavgPrecip Tmn Tmx Tavg Prec.
1.0
NAO 0.8
-2.0
-1.5
Temperature
-1.0 0.6
-0.5 Dynaric Alps Pyndos Balkan M. Carpathian
0.0
0.4
0.5
1.0
1.5 0.2
2.0
0.0
0.0 0.2 0.4 0.6 0.8 0.0
1.0 0.2 0.4 0.6 0.8 0.0
1.0 0.2 0.4 0.6 0.8 1.0
0.0 0.2 0.4 0.6 0.8 1.0
Precipitation Precipitation Precipitation Precipitation
3
Dynaric Alps Pyndos Balkan M. Carpathian
2
NAO (DJFM)
1
0
-1
-2
-3
WW WD CW CD WW WD CW CD WW WD CW CD WW WD CW CD

18. 1.0
Taurus N. Turkey Caucasus Lebanon
Taurus 0.8
0.6
N. Turkey
Coefficient of correlation
0.4
Caucasus
0.2
0.0
Lebanon -0.2
-0.4
-0.6
-0.8
-1.0
Tmx Tmn Tavg Prec. Tmx Tmn Tavg Prec. Tmx Tmn Tavg Prec. Tmx Tmn Tavg Prec.
Tmn Tmx TavgPrecip Tmn Tmx TavgPrecip Tmn Tmx TavgPrecip Tmn Tmx TavgPrecip
NAO
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
3
Taurus N. Turkey Caucasus Lebanon
2
NAO (DJFM)
1
0
-1
-2
-3
WW WD CW CD WW WD CW CD WW WD CW CD WW WD CW CD

19. ANOVA TEST
WW WD CW
WD CW CD CW CD CD
Cantabrian M. X O O X O O
Central S. X O O X O O
Pyrenees X O O X X X
S. Nevada X O X X O X
Atlas O O X O O X
Alpes O O O X X O
Apenines O O O O O X
Carpathian M. X O O O O O
Dynaric Alps X O O X O O
Pindos X O X O O X
Balkans O O O O O X
Taurus O O X O O O
N. Turkey O O O O X O
Caucasus O O O O O O
Lebanon O O O O O O
X diference is significant at α<0.05

20. What do the models inform for the next
century?
Simulated temperature and precipitation simulated for each mountain system, and NAOi for
the period 1900 and 2099 by 10 different GCMs were used to:
-Asses the capability of GCMs to reproduce the observed relationship between precipitation
and temperature and NAOi across the Mediterranean area
-Assess if relationships between NAO and winter modes observed in the last century are
expected to continue during the 21st century
SRES A1B

21. Distribution of observed (OBS) and simulated winter NAO values for
the 20th (C) and 21st (F) centuries
2.0
1.5
1.0
0.5
NAO values
0.0
-0.5
-1.0
-1.5 C F C F C F C F C F C F C F C F C F C F
OBS MRI MPI MIUB MIROC GFDL CSIRO CNRM CCMA BCM UKMO
-2.0

22. Simulated correlation between NAOi and precipitation for the control
period (1950-2006)

23. Simulated correlation between NAOi and precipitation for the control
period (1950-2006) and 21st century (2000-2099)

24. Simulated correlation between NAOi and temperature for the control
period (1950-2006) and 21st century (2000-2099)

25. Average NAOi for different winter modes during the control period (C,
1950-2006) and the 21st century (F. 2000-2099)
1.5
Pyrenees Alps
1.0
Mean NAOi (DJFM)
0.5
0.0
-0.5
-1.0
C F C F C F C F C F C F C F C F
WW WD CW CD WW WD CW CD
-1.5
1.5
Pindos Lebanon
1.0 MRI
MPI
MIUB
Mean NAOi (DJFM)
0.5 MIROC
GFDL
CSIRO
0.0 CNRM
CCMA
BCM
UKMO
-0.5
Model average
Observed
-1.0
C F C F C F C F C F C F C F C F
WW WD CW CD WW WD CW CD
-1.5
WW WW_F WD WD_F CW CW_F CD CD_F

26. Number of GCMs which show significant differences in NAOi according
to different winter modes during the control period (1950-2006) and
21st century (2000-2099)
WW WD CW
WD CW CD CW CD CD
Cantabrian M. 4 0 3 6 1 1
Central S. 6 0 5 6 0 4
Pyrenees 6 0 1 7 4 4
S. Nevada 5 0 7 5 2 5
1950-2006 Atlas 2 3 9 0 3 3
Alpes 1 1 0 6 5 1
Apenines 2 1 4 4 0 1
Carpathian M. 5 1 0 2 1 0
Dynaric Alps 6 2 0 1 0 1
Pindos 5 1 6 0 1 2
Balkans 0 1 4 0 1 1
Taurus 0 1 2 1 2 1
N. Turkey 0 1 1 0 1 2
Caucasus 0 2 1 0 0 0
Lebanon 0 2 2 1 2 0
WW WD CW
2000-2099 WD CW CD CW CD CD
Cantabrian M. 8 2 2 8 3 3
Central S. 8 1 7 9 2 7
Pyrenees 9 2 3 10 2 7
S. Nevada 8 0 8 8 1 9
Atlas 5 2 8 3 2 7
Alpes 7 1 3 8 7 4
Apenines 7 1 2 7 3 4
Carpathian M. 8 3 2 9 3 4
Dynaric Alps 9 0 4 6 1 6
Pindos 8 0 8 3 3 3
Balkans 2 1 4 2 3 4
Taurus 0 2 5 1 4 2
N. Turkey 0 1 2 1 1 0
Caucasus 1 2 4 1 1 0
ANOVA TEST Lebanon 0 3 5 0 3 2

27. Change in temperature and precipitation simulated by 10 GCMs
2000-2099 period compared to 1950-2000
3.5
Temperature 3.0
Change in temperature (ºC)
2.5
2.0
1.5
1.0
MRI 0.5
40
MPI
Precipitation
MIUB 30
MIROC
Change in precipitation (%)
20
GFDL
10
CSIRO
CNRM 0
CCMA -10
BCM
UKMO -20
-30
Model average
Observed -40
Cant.M. S.Cent. Pyr. S.Nev Atlas Alps Apen. Carp. Dyn.A. Pynd. Balk. Taur. N.Turk.Cauc. Leb

28. Change in the number of winters belonging to different winter modes
during the 21st using the percentiles of the period 2000-2099 (C) and
1950-2000 (F)
30
Cold and wet
25
Number of winters
20
15
10
5
0
CF CF CF CF CF CF CF CF CF CF CF CF CF CF CF
35
Cold and dry
MRI 30
MPI 25
Number of winters
MIUB 20
MIROC
15
GFDL
CSIRO10
CNRM 5
CCMA
0
BCM CF CF CF CF CF CF CF CF CF CF CF CF CF CF CF
UKMO Cant.M.S.Cent. Pyr. S.Nev Atlas Alps Apen. Carp. Dyn.A. Pynd. Balk. Taur. N.Turk. auc. Leb
C
Model average

29. Change in the number of winters belonging to different winter modes
during the 21st using the percentiles of the period 2000-2099 (C) and
1950-2000 (F)
100
Warm and wet
Number of winters 80
60
40
20
0
CF CF CF CF CF CF CF CF CF CF CF CF CF CF CF
100
Warm and dry
MRI
80
MPI
Number of winters
MIUB 60
MIROC
GFDL 40
CSIRO
CNRM 20
CCMA
BCM 0
CF CF CF CF CF CF CF CF CF CF CF CF CF CF CF
UKMO
Cant.M.S.Cent. Pyr. S.Nev Atlas Alps Apen. Carp. Dyn.A. Pynd. Balk. Taur. N.Turk. auc. Leb
C
Model average

30. Conclusions
NAO exerts a strong influence on the occurrence of different winter modes across
the mediterranean area
- In the Iberian Peninsula, Atlas, Balkans and Greece it mainly causes differences
between wet and dry modes.
- In the Alps, Taurus and Lebanon NAO introduce significant differences between cold
and warm modes
The occurrence of winter modes has a major influence on the accumulation of snow
in the mountain areas. Hence, NAO pattern is an important driver of the interannual
variability of snowpack.
0.2
3
NAO (DJFM)
2 A 0.0
Pearson´s correlation coefficient
1 µ = -0.36
0 4 B
-1 -0.2
Snow depth (-)
-2 2
-3
3 0
µ = -0.48
Snow depth (-)
-0.4
2
1 -2
0
r= - 0.59
-0.6 -1 -4 p< 0.05
-2
-3 -2 -1 0 1 2
Values above de average
-0.8
Values below the average NAO (DJFM)
Number of Number of Number of
cases: 86 cases: 24 cases: 62
-1.0
All snow poles Snow poles Snow poles
below 2100 m above 2100 m

31. Conclusions
GCMs have shown a reasonable skill for reproducing NAO variability, most of
simulations project an increase in NAO for the next decades
GCMs reproduce adequately the observed correlations between NAO and precipitation
across the basin, and they have a lower capability for reproducing correlations with
temperature. In general, the influence of NAO in the ocurrence of contrasted winter
modes is well simulated. Such influence tends to be maintained, even strengthed in the
next decades.
These results suggest that the projected upward trend of NAO in the next decades may
lead to higher frequency of winter modes unfavourable for snowpack development
An expected increase of temperature (1.5-2ºC) will cause that the number of cold
(warm) winters as observed during the 1950-2000 period will decrease (increase)
dramatically in the 21st century.

32. Conclusions
Thanks!