Regional and local climatic effects on the Dead-Sea evaporation

-A novel method to separate the regional factor

H. Shafir and P. Alpert

Dept. of Geophysics and Planetary Sciences,

Tel Aviv University

Submitted to: Climatic Change

December, 2008

P. Alpert, H. Shafir and D. Issahary, "Recent changes in the climate of the Dead Sea Valley", Climatic Change, 7, 1-25, 1997.

Earlier Work:Wind, temperature and humidity measurements at the Dead Sea starting in the 1930s as well as 3-D model simulations all seem to indicate a statistically significant change in the local climate of the 3Dead Sea region.

ANNUAL EVAPORATI ON AT STATI ONS I N THE JORDAN VALLEY AND THE ARAVA

100

150

200

250

300

350

400

450

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

YEAR

AN

NU

AL

EV

AP

OR

AT

IO

N

(C

M/

Y)

Elat Masada Yotveta

Tirat- Zvi Jericho Sdom 1st stat ion

Sdom 2nd stat ion Beit Dagan

Param. MonthHour

Jan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.

08+1.1***

+1.0***

===+0.4* *

+0.7***

+0.6* *

==+1.1***

+1.4***

T(C)

14====+0.8*

=+1.0***

=+0.4*

==+0.9*

20+1.3***

+1.0*

==+1.2***

+0.9***

+1.5***

+1.0***

+0.6* *

=+1.2***

+1.6***

08=======+1.2*

====

RH(%)

14======-1.8*

=====

20======-2.7* *

=-3.0***

=-4.4* *

=

08+0.9*

=+0.9*

====+0.5* *

====

WS(m/sec)

14==+1.1* *

+1.0*

========

20=+1.3***

+1.0*

+0.9*

+0.7*

+1.5* *

===+0.9* *

+0.9***

+0.7*

EVAP (cm)monthly+1.9***

+2.8***

+3.8***

+5.8***

+5.0***

+4.3***

+5.5***

+5.8***

+4.6***

+2.7***

+4.6***

+2.1***

Sdom

Significant changes of the average hourly meteorological parameters at Sdom. New period (1995-2004) against previous period (1970-1994)

Param. MonthHour

Jan.Feb.Mar.Apr.MayJun.Jul.Aug.Sep.Oct.Nov.Dec.

08+0.8*

=====+1.0***

+0.6*

==+0.8*

+0.9* *

T(C)

14+0.9*

=====+0.8***

===+0.8*

+1.2***

20+1.3***

===+1.1***

+1.0***

+1.7***

+1.2***

+0.8***

+0.7* *

+1.2***

+1.4***

08===+2.3*

=+2.9***

=+2.0* *

=+2.1*

==

RH(%)

14=====+1.6***

=+1.5*

=+2.8***

==

20======-1.6*

====-3.0*

08============

WS(m/sec)

14============

20=+0.7*

=+0.6*

=+0.9***

+1.0***

+1.0***

+0.8***

+0.6*

==

EVAP (cm)monthly============

Eilat

Significant changes of the average hourly meteorological parameters at Eilat. New period (1995-2004) against previous period (1970-1994)

Average daily evaporation in Sdom in the different synoptic systems for the period 1964-2006

0

2

4

6

8

10

12

14

16

Ave

rage

dai

ly e

vapo

rati

on (

mm

)

The relative contribution to the annual evaporation at Sdom of the synoptic system RST-Eastern axis for 1964-2006. Trend line included.

0

2

4

6

8

10

12

14

16

18

20

1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Cont

ribu

tion

(%

)

The relat ive contribut ion to the annual evaporat ion at Sdom of the synopt ic system Weak Persian t rough for 1964-2005 . Trend line included.

02468

101214161820222426283032

1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Cont

ribut

ion

(%)

The relat ive contribut ion to the annual evaporat ion at Sdom of the synopt ic system Medium Persian t rough for 1964-2005 . Trend line included.

0

4

8

12

16

20

24

28

32

36

40

44

48

1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Cont

ribut

ion

(%)

The relat ive contribut ion to the annual evaporat ion at Sdom of the synopt ic system High to the West for 1964-2006 . Trend line included.

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004

Year

Cont

ribut

ion

(%)

The total change in the average annual E can be written as:

i

iiiiss fEfEEEE )( 606020002000602000

i

iiiiii fEffEEE ]))([( 60606060

i

iiiiii fEfEfEE ][ 6060

i

iiii fEEfE ][ 6060

where:

602000, ii EE represent the mean evaporation for synoptic system (i)

in the 2000s and 1960s, respectively,

602000, ii ff represent the mean frequency of synoptic system (i) in

the 2000s and 1960s, respectively, and:

iE , if represent the changes of the intrinsic evaporation and

frequency respectively from the 1960s to the 2000s in each synoptic

system i.

Sdom Evaporation Change 2000s Compared to 1960s

The term ii fE was found very small and negligible (order of 10-1

and lower).

Therefore, the equation above can be rewritten as;

)( ii

i EvFrE

Where 60iii EfFr is the frequency change contribution, and

60iii fEEv the intrinsic evaporation change contribution for the i synoptic system.

Contributions to the increase in the annual evaporation in Sdom of the different synoptic systems (1996-2005 minus 1964-1974 averages)

-250

-200

-150

-100

-50

0

50

100

150

200

250

300

350

400

Synoptic system

an

nu

al t

ota

l dif

fere

nce

(m

m/y

)ΔĒ

Contributions to increase in the annual evaporation in Sdom (1996-2005 averages minus 1964-1974) as a result from the higher daily evaporation in each system.

-250

-200

-150

-100

-50

0

50

100

150

200

250

300

Synoptic system

An

nu

al d

iffe

ren

ce (

mm

/y)

Εvi

contributions to increase in the annual evaporation in Sdom (1996-2005 averages minus 1964-1974) due to change in frequency of each synoptic system

-250

-200

-150

-100

-50

0

50

100

150

200

250

300

Synoptic system

An

nu

al d

iffe

ren

ce (

mm

/y)

Fri

Summary and conclusions

• The evaporation from the Dead-Sea is important to the local industries. It was found that the pan evaporation in Sdom has increased by about 70 cm/y from the 1960s to the 2000s.

• One explanation is that the rise in evaporation is a local phenomenon because of the drying of the lake. This drying has caused the local Dead-Sea breeze intensity to reduce. This breeze that used to temper the climate has therefore caused the temperature to increase, the relative humidity to decrease, and thus it causes the pan evaporation to increase in Sdom.

• Another local climate change is the intensification of the Mediterranean breeze entering the Dead-Sea as a result of the reduced interaction of this wind with the opposing but weakened Dead-Sea breeze.

• A very different contribution to the evaporation rise is the increasing effect of the global warming. The hotter and drier synoptic systems have increased their frequencies. The Red-Sea Trough which is a hot and dry system has nearly doubled in frequency during last 50 years. Also, the hottest system of the year-the Weak Persian Trough has increased frequencies on behalf of other cooler summer systems.

• Most of the 70 cm/y evaporation increase were due to the intrinsic evaporation rise in the Red-Sea trough (about 30 cm/y) and the Weak Persian Trough systems (about 40 cm/y).

• It was found that both the global as well as the local effect are contributing to the evaporation increases. It seems that till the 1990s the local effect was the dominant one, while later on probably the large-scale effect due to the global warming becomes the dominant factor of the evaporation increase at the Dead-Sea.

Wind channeling by the Dead-Sea wadis

By:

H. Shafir, F. Jin, Y. Lati, M. Cohen and P. Alpert

The Open Atmospheric Science Journal

2 ,139-152 ,2008

The south Dead-Sea satellite picture of observational stations (in red) and wadis (in

blue) used in this study

Surface wind flow pattern (black arrows, unit is m/s), contour of topography (red, dot red line indicates the negative height of topography with interval 50 meters) and contour of wind divergence (blue, dashed, unit is ·10-4 s-1, contour interval 2·10-4s-1)

for the Zeelim Wadi at 3:00 UTC 6th Sep 2005

Zeelim Wadi Flow at 3:00 UTC 6th Sep 2005

Same as previous figure, but for the Chemar Wadi

No. Altitude

(m) Velocity

(kt) Direction

(deg) Wind Vector

1 Ground-wind 4.0 330

2 0 - 150 10.5 330

3 150 - 300 8.1 346

4 300 - 450 15.6 008

5 450 – 600 15.5 012

6 600 – 750 14.8 024

7 750 – 900 13.7 018

8 900 – 1060 14.8 019

Table 1.1: Vertical profile of the wind speed (kt) and direction from the ground to 1000m elevation. The profile

was measured by a radiosonde on the 5 Sept., 2005 21:00 LT at Nve-Zohar.

Date Time P8

Velocity (m/sec)

P8 Direction

(deg)

P8 Wind Vector

P5 Velocity (m/sec)

P5 Direction

(deg)

P5 Wind Vector

5/9/05 19:00 6.0 337

6.3 007

5/9/05 19:30 8.3 323

6.2 005

5/9/05 20:00 12.4 324

8.4 306

5/9/05 20:30 10.1 327

9 309

5/9/05 21:00 9.8 327

9.2 308

5/9/05 21:30 8.7 333

7.5 321

5/9/05 22:00 9.4 333

7.2 355

5/9/05 22:30 9.5 337

8.0 342

5/9/05 23:00 9.6 346

6.2 355

5/9/05 23:30 9.3 336

6.6 008

6/9/05 00:00 9.2 345

5.1 357

6/9/05 00:30 7.1 340

4.2 005

6/9/05 01:00 5.7 345

2.9 337

6/9/05 01:30 4.9 327

3.6 347

6/9/05 02:00 5.3 319

2.4 027

6/9/05 02:30 5.6 335

2.1 002

6/9/05 03:00 4.1 318

3.1 324

6/9/05 03:30 5.2 326

3.8 315

6/9/05 04:00 5.8 313

4.9 313

Average 7.68

Range 313 - 346

Average 5.62

Range 306 - 027

Table 2: Time series of the wind speed (m/sec) and direction measured at the ground stations of P8 and P5,

from 5 Sept., 2005, 19:00 till 6 Sept., 04:00 every half hour. At the bottom the averages are displayed along with

the range of the directions.