impacts of nao on the hydrology of eastern mediterranean

1Istanbul Technical University / Civil Engineering Department

Impacts of NAO on the Hydrology of

Eastern Mediterranean

Ercan KahyaIstanbul Technical University


Outlines

1. A General View on NAO impacts in EM

2. Findings in M.E. Countries

3. Findings in Turkey

4. Conclusions


How do we expect NAO signals in Eastern Mediterranean (EM)? NAO Positive Phase NAO Negative Phase

- STRONGER than usual surface winds & wintertime storms from west to east- COOLER and DRIER winters in EM

- WEAKER than usual surface winds & wintertime storms from west to east- WARMER and WETTER winters in EM

http://www.ldeo.columbia.edu/NAO/NAO-.gif

http://www.ldeo.columbia.edu/NAO/NAO+.gif


NAO-Precipitation Variability in M.E. (Cullen et al.: 2002)DJFM Composite Anomalies (1979-1998)

Most negative quartile of NAO index years

Most positive quartile of NAO index years


NAO-Streamflow in M.E.

(Cullen et al.: 2002)

Accumulated ppt for the periodNov-Apr / 1998–1999 to 2000–2001

Location of Streamflow stations

- EOF analysis on 12 monthly subsamples of the interpolated records of 5 rivers- EOF 1 loadings at all stations are almost always positive, showing a common signal- EOF 1 accounts for 70% of total variance during DJFM and 60-90% during AMJJ

CONCLUSION: DJFM streamflow is most strongly influenced by the NAO


NAO-Precipitation & Temperature in M.E.

(Cullen & deMenocal: 2000)

Spatial correlation between the NAOSLP index and mean winter (DJFM) station (a) temperature; and (b) precipitation

DATA: 211 temperature and 403 precipitation stations 30-year long


NAO-Precipitation in Mediterranean (Oleg Pokrovsky: 200?)

Seasonal correlation of April-May (1995-2005) precipitation with February-March NAO(index leads by 2 months)

Seasonal correlation of April-May (1965-1975) precipitation withFebruary-March NAO(index leads by 2 months)


NAO-Precipitation in Mediterranean (Oleg Pokrovsky: 200?)

Seasonal correlation of June-July (1995-2005) precipitation with April-May NAO(index leads by 2 months)

Seasonal correlation of Sep-Oct (1995-2005) precipitation with July-August NAO(index leads by 2 months)


NAO Signals in Iran NAO-Regional Meteorological Drought

(Dezfuli, et al.: 2010)

• NAO negatively correlated with autumn rainfall [extreme autumn drought - the negative June–Aug NAO]

• A spring drought is preceded by an Oct–Dec NAO > 0.5

• Winter droughts – not lag correlated with NAO

• A wet autumn tends to occur when June–Aug NAO < −0.3

• Wet winter seasons – not lag correlated with NAO


NAO Signals in Kuwait NAO-Rainfall (Marcella & Eltahir: 2010)

• No significant correlation on a monthly or yearly time scale

• Weak connections observed with both tropical and mid-latitude atmospheric systems

• Reason: Kuwait is located in the transitional zone between the tropics and mid-latitudes

Spatial Correlation:

CRU’s Kuwait rainfall & surrounding rainfallfor November–April


NAO Signals in Oman NAO-Rainfall (Charabi & Al-Hatrushi: 2010)

• Wet and dry spells - composite analysis - period 1984-2007 – reanalysis data used

• Circulation features over the Caspian region responsible for winter rainfall variability

• Dry spells – NAO (+) weak correlation (r=0.22)

• Wet spells – negatively correlated with NAO (r=0.45)

• Reason: NAO (-) phase → enhanced westerly flow (850-hpa up to 200-hpa), bringing more moisture from Atlantic Ocean across the Mediterranean area

Annual average of rainfall 1984–2007

Winter average of rainfall 1984–2007


NAO Signals in Israel NAO-Rainfall Intensity (Yosef et al.: 2009)

• Six rainfall categories - rainy season (Oct-May) - period 1950-2003

• A (light: 0-4 mm/d), B (moderate), A&B (light to moderate), C1 (moderate-heavy), C2 (heavy), and D1 (heavy-torrential: 64-128 mm/d)

• NAO - significant impacts in center and south parts

13Istanbul Technical University/Civil Eng Dept.

NAO Signals in Turkey NAO-Precipitation, Temperature &Tigris–Euphrates Streamflow

(Cullen & deMenocal: 2009)

Data period: 1930–1995 Stations: 23 temp & 27 ppt

Correlation btw the NAOSLP index and (a) Turkish winter temperature index

(b) Turkish winter precipitation index

(c) DJFMA average streamflow of the Euphrates (filled circles) and the Tigris Rivers (open circles)Results:18% of the temperature variance is linearly related to the NAOSLP index

27% of the Turkish winter precipitation variance is linearly related to the NAOSLP index

14Istanbul Technical University/Civil Eng Dept.

NAO Signals in Turkey NAO-Tigris–Euphrates Streamflow (Cullen & deMenocal: 2009)

- More profound NAO influence when NAO-extrema years are considered

- At Keban station, the Euphrates streamflow exhibits 40% variability about the 35-year mean value (663 m3/s) associated with NAO extrema


NAO Signals in Turkey NAO-Rainfall (Turkes: 1996)

Rainfall in Turkey is characterized by two major wet periods: [1940 – 1948] and [1962 – 1970] by two major dry periods: [1971 – 1974] and [1989 – 1993] with severe and widespread droughts occurring in 1973, 1984, 1989 and 1990.

When compared with the NAOSLP index shown in figure (a) in page 12, a connection between wet periods and a negative NAO, and drought periods and a positive NAO.

NAO-Temperature (Turkes & Erlat: 2009)Investigated monthly mean winter (DJF) air temperature series at 70 stations in Turkey

During NAO+ phase: - Northeasterly circulation increased, thus spatially coherent and significant cold signals

During NAO- phase: - Spatially coherent and significant warm signals - Increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey


NAO Signals in Turkey

NAO-Precipitation

NAO-Streamflow

(Karabörk, Kahya, Karaca: 2005)



NAO-Tmax

NAO-Tmin

(Karabörk, Kahya & Karaca: 2005)


NAO Signals in Turkey NAO-Streamflow PC1

(Kalayci & Kahya: 2006)

• Basic streamflow anomaly pattern

• Reproduces 38.2% of the total variance

• Period 1964-1994


NAO Signals in Turkey NAO-PC1

(Kalayci & Kahya: 2006)

• PC1 as indicator of general level of streamflow

• Highly significant relation for Annual and JFM


NAO Signals in Turkey NAO-Lake Levels (Kucuk, Kahya et al.: 2008)

• 7 lakes selected among 25 lakes with the period 1960-2002

• Using continuous wavelet transform analysis,

- Relations Lake-level Periodicities & those of NAOI


NAO Signals in Turkey NAO-Lake Levels (Kucuk, Kahya et al.: 2008)

• Periodicities with 5- to 24-year scale level in Iznik, Beysehir & Egirdir lakes

• Uluabat, Sapanca & Tuz lakes are in-phase relation with NAO periodicities less than 10-year & found to be more prone being affected by NAO


NAO Signals in Turkey NAO-PDFs of Critical Droughts

(Sarlak & Kahya: 2006)

• Göksu River / Annual data (1936 -2000)

• Two periods for NAO+ & NAO- (1936-1971)&(1972-2000)

Model: A first-order Markov chain selected based on AIC & BIC

Result: Expected critical drought durations E(L):For example, say L=25, then E(L)=14.34 years for the NAO+ period, whereas E(L)= 6.17 years for the NAO- period.


NAO Signals in Turkey NAO-PDFs of Critical Droughts (Sarlak & Kahya: 2006)

Observed Transitional Probabilities for the Entire Period 1936–2000Results:

- Surplus probability P(s), wet flow conditions, increases to 0.583 for the NAO- period

- The reverse is true for deficit probability P(d)

-Probability P(d/d), characteristic of negative anomaly followed by another negative anomaly, takes on a remarkably high value of 0.812 for the NAO- period


NAO Signals in Turkey NAO-Annual Cycle Modulation

(Guney, Kahya et al.: 2008)

NAO Index Categorization

Çoruh Basin (Northeastern Turkey)


NAO Signals in Turkey NAO-Hydrologic Regionalization (Kahya et al.: 2010)

NAO NEGATIVE PHASE– 40 STATIONS

Data Period: 1970-1997

NAO POSITIVE PHASE – 83 STATIONS

Data Period: 1962-1971

Method: Cluster Analysis

26


(Hydrologic Regionalization)

Qmax

Qave

Qmin

NAO+ Phase NAO- Phase


NAO Signals in Turkey Cyclone Track Climatology (Karaca et al.: 2000)

DATA: Daily surface and 500-hPa charts for the period 1979-1994

PATH 1: Originates from the southwestern Russia

PATH 2: Originates from the Balkans

PATH 3: Originates from the Genoa Gulf PATH 3a: Moves to the northeast direction PATH 3b: Moves towards the east

PATH 4: Originates from the western/middle Mediterranean or from southern Genoa Gulf or from north of the Sahara Desert


NAO Signals in Turkey Cyclone Track Climatology (Karaca et al.: 2000)

(a) Frequency of cyclones over Turkey (b) Cyclone numbers in months

RESULT: For Turkey’s Mediterranean type of climate: the number of cyclones is the lowest in the summer and highest in the winter

MISSING INDICATION: The period 1979-1994 corresponds the NAO+ period, so it is consistent to observe insignificant decreasing trend implication in the first panel


Conclusions

Ercan KahyaIstanbul Technical University

- NAO signals are detectable in Turkish climate/hydrological surface variables- No evidence for rainfall in Kuwait- Wet spells in Oman rainfall are significantly and negatively correlated with NAO- Significant rainfall intensity relations with NAO in central & southern Israel- Autumn rainfall/drought and spring drought in Iran significantly correlated with NAO

Suggestion: A regional study in EM as a whole with dense data network including major climate variables is needed …

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