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The relation between the 18O and deuterium contents of rain water in the Negev Desert and air-mass trajectories
Isotope Geoscience, 1 (1983) 205-218 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
205
THE RELATION BETWEEN THE 18 0 AND DEUfERIUM CONTENTS OF RAIN WATER IN THE NEGEV DESERT AND AIR-MASS TRAJECTORIES
CLAUDE LEGUY', MICHAEL RINDSBERGER 2,3 A. ZANGWIL', ARIE ISSAR' and JOEL R. GAT3 '
"Jacob Blaustein Institute for Desert Research and Geological Department Ben Gurion University of the Negev, Beer-Sheua (Israel) 'Israel Meteorological Service, Bet Dagan (Israel) 'Department of Isotope Research, The Weizmann Institute of Science, Rehovot (Israel) (Received November 15, 1982; revised and accepted May 17, 1983)
ABSTRACT Leguy, C1., Rindsberger, M., Zangwil, A., Issar, A. and Gat, J.R., 1983. The relation between the 18 0 and deuterium contents of rain water in the Negev Desert and air-mass trajectories. Isot. Geosci., 1: 205-218. Sampling of rain water was carried out in the Negev, Israel, from 1978 till 1981, by means of a self-sealing sampler which enables the sampling of each separate rain storm, as well as parts of each storm. The relation between the isotopic composition and various synoptic parameters is discussed. Based on "deuterium excess" values, the rain samples can be separated into three groups. The majority of the samples have a "deuterium excess" between 10 and 22%°' These samples have different histories from the meteorological point of view. However, there are two extreme groups, one has "deuterium excess" values above 22%0 and the other has values less than 10%0' It was found that the rains which are most depleted with regard to deuterium and with the lowest "deuterium excess" values are associated with air masses that reach the region concerned from the southwest. Rains with a "deuterium excess" of more than 22%0 are associated with air masses which come mainly from northeastern Europe and reach the considered region from west to northwest, following intense interaction with the central-eastern Mediterranean Sea.
INTRODUCTION
The Negev forms the southern arid half of Israel. The average annual precipitation over most of this area is less than 200 mm (Fig. 1b) (I.M.S., 1977). The Negev forms part of the desert belt extending from the Sahara through Cyrenaica, Egypt, and the Sinai to the Arabian Desert. Owing to its location close to the southeastern Mediterranean coast, it is relatively more affected by the winter cyclonic region of the Mediterranean Sea than the deserts of eastern North Africa (Evenari et al., 1971).
0167-6695/83/$03.00
©
1983 Elsevier Science Publishers B.V.
206
The Mediterranean winter precipitation in the Levant shows, on the average, a distinctive isotopic character with a relatively large excess of the d parameter* (Gat and Carmi, 1970). The influence of the Mediterranean regime can also be traced in the meteoric waters of the Negev and Sinai deserts by the contents of 18 0 and deuterium (Gat and Issar, 1974). On the other hand, comparison of data from the more humid northern part of the country with some major storms in the Negev, shows more depleted isotopic values than expected in the latter (Levin et al., 1980). In contrast to the abovementioned cases, one also occasionally encounters rains which are enriched in the heavy isotopic species. These rains have a very low tritium content and their origin has been related to air masses coming from the Indian Ocean. In this study, ·some synoptic aspects are considered with regard to the isotopic composition of rain . Any such relationship might also throw additional light on the climate of this region at the time that the paleowaters of this region were formed (recharged). It has been noted that the isotopic composition of the Sinai and the Negev paleowaters (average values 5 18 0 = -6.95%o, oD = -49%0, d = 7% 0) (Gat, 1981), is distinct from the mean composition of meteoric waters of the Mediterranean cyclonic regime (018 0 = -5.57%0; oD = -22.9%0' Bet Dagan) (I.A.E.A., 1981). ISOTOPIC DATA
The isotopic data set, discussed in this study, consists of ~ 150 samples taken at Avdat (A), Beer-Sheva (B), Sde Boqer (S), Sadot (E), Mizpeh Ramon (M) and Revivim (R ), as reported by Levin et al. (1980). This data set has been supplemented by recent measurements taken at the above-mentioned locations and, in addition, at Zavoa (Z). These seven stations are distributed throughout the central Negev (Fig. 1b). At three of the stations (R , Z, S) a multiple rain sampler (Adar et al., 1980) was used. In this sampler, once the collection flask contains 500 em" of water, representing 2 mm of rain, it is sealed hermetically and an overflow mechanism enables any succeeding amount of rain to be sampled, up to a total of 12 mm. At the other stations, rain-water samples were collected from standard Israel Meteorological Service rain recorders. Analyses for the isotopic composition of the water samples esO, D and tritium) were performed at the Isotope Laboratory of the Weizmann Institute of Science. 18 0 and deuterium are reported in 0 (%0) units relative to SMOW in the accepted manner. Tritium is reported in tritium units (TV). The average reproducibility of the stable-isotopes measurements was ± 0.15%0 for 0 18 0 and % ± 1.5 0 for oD; the error of estimate of the derived quantity d is then of the order of ± 2.7%0' The original data set consisted of '" 150 samples. However, preliminary isotope analysis showed that the isotopic data of rain events with amounts of *d , the deuterium excess, is defined as d = c5 D-8c5 18 0 ; the d-value is established in the atmospheric part of the water cycle in the source areas of the vapour.
207
a
a.
o
extremly arid
~ arid
I""o'd semi-arid b.
station elevation
/{p isohyet [1 J
28"
34"
35"
Fig . 1. Location of study area: (a) general context map of arid zones; and (b) rainfallcollecting stations in the Negev Highlands.
rain less than 2 mm were rather erratic. The isotopic composition of lowintensity rains is possibly distorted by the fractionation which accompanies the evaporation of the falling rain drops. Hence, in our study we considered only those events in which the rain amount was equal to or greater than 2 mm. It was found, also, that the mean scatter range of values from the various collection stations on any given rain day (an order of ± 1%0 in 8180) was significantly less than the scatter of the daily averages from different rain days (an order of ± 2%0 in 8180). Considering a large-scale pattern, we may assume that rain events, on any particular day, are affected by the same synoptic conditions. Therefore, it seems justified to discuss these data on the basis of the weighted mean isotopic composition for each precipitation event (rain day). For each event their amount-weighted means of the isotopic composition were calculated for all the measurements taken on the same day: n
8%0 (weighted) = 1/P~8iPi 1
208
where Pi = daily amount of rain at station i; (if Pi (precipitation) > 2 mm); p = ~~ Pi; and n = number of stations considered (1 up to 7). The calculated weighted means are given in Table 1. The span of the isotopic composition data for the different rain days is rather wide and ranges from - -8 to -1%0 for li 18 0 and -75 to -10%0 in liD. No systematic amount-effect could be observed in this data set. The li18 0 _ and liD-values are, however, rather well correlated along meteoric water lines, with ~ 80% of the data showing a deuterium excess of between +10 and +30%°' d = +15%0 on the average. METEOROLOGICAL DATA
For the synoptic meteorological analysis, we used surface and 700-mbar synoptic charts and upper air measurements taken at Bet Dagan, Israel, which is situated - 100 km north of the region considered. These measurements include the tropopause level, the temperature and relative humidity at various other levels. Air-mass trajectory characterization is based on 700-mbar synoptic charts for the three days preceding the rain event. The general flow is characterized by the so-called "zonal index". The index has been calculated between Cairo, Egypt (62,378) and Ankara, Turkey (17,130), from the 700-mbar chart. It should be kept in mind that a high index indicates a tendency toward zonal flow, whereas a low index represents a tendency toward meridional flow, positive when the pressure increases southward and negative when the pressure decreases southward. Applying the method suggested by Barry and Perry (1973), air-mass trajectories were determined, based on 700-mbar charts. The trajectories were classified as follows (Gagin and Neumann, 1974): We trajectory, represents trajectories whose main direction is from west and whose air masses travelled most of the time over the Mediterranean Sea. Nw trajectory, represents trajectories whose main direction is from north to northwest, and whose air masses travelled most of the time over the European continent. So trajectory, when the main direction is from the south, and the air masses travelled most of the time over the African continent. It should be mentioned that Gagin and Neumann's (1974) analysis includes also another type of trajectory. However, in the sample under study this type has not been associated with any of the rain events in the considered region. A "source" term is defined as the region in which the air mass was located 72 hr. before reaching the Negev Highlands. We classified the "sources" into three categories as follows: Source X - West Europe and the Atlantic Source Y - north of Central and East Europe Source Z - the south, mainly Africa
209
Examples of the different types of trajectories under study are shown in Fig. 2.
~ --- ~
24: day OOH. recording GMT 12H. recording GMT intermediate time Nw trajectory _ ._.- We trajectory ------ So trajectory (NEGEV RAINFALL from 24.2.78;12.1278;2.1. c
•
IOf
Fig . 2. Trajectories types, based on 700-mbar synoptic charts.
RESULTS
The frequency of occurrence of the various trajectories in the present study, together with a summary of some statistical parameters sorted according to trajectory type and "source", is given in Table II. It seems that on the average the southern trajectory may be characterized by rains which are often depleted in the heavy stable isotopes, with significantly lower "deuterium excess" values in comparison to the other trajectories. Yurtsever (1975) found a rather high correlation between the mean monthly b 180 -values and the mean monthly surface temperature at some stations. Hage et al. (1975) found a high correlation between mean annual b 180-values and mean annual 800-mbar temperatures. In our study, which refers to individual storms, no such high correlation was found. However, there seems to be a trend of increasing values of b 180 and bD with the tropopause level (Fig. 3a and b), with correlation coefficients 0.51 and 0.56, respectively . This may indicate a dependence of isotopic composition on the air-mass temperature, as the tropopause level is strongly correlated with the mean temperature of the tropospheric air column.
t.:l I-'
o
TABLE I Isotopic composition ofrain in the Negev, 1977-1980 Year
Month
Day
6'
10
(%0)
6D (%0)
d (%0)
Tritium content
Trajectory*
Source*
Average Range of Stations* precipitation precipitation (mm) (mm)
-
-
3.2 3.9 3.2 5.2 7.1 5.1 12.9 3.3 13.6 7.7 4.6 2.8 9.2 6.0 7.9 4.1 4.3 5.2 2.2 19.9 16.7 3.1 3.9
(T.V.)
1977 1977 1977 1977 1977 1977 1977 1977 1977 1977 1978 1978 1978 1978 1978 1978 1978 1978 1978 1978 1979 1979 1979
10 11 11 11
12 12 12 12 12 12 1 1 2 2 3 3 3 4 12 12 1 1 1
29 2 11
12 6 12 14 21 22 23 2 3 23 28 13 29 30 24 11 12 8 9 21
-0.76 -1.61 -0.82 -2.17 -2.43 -5.27 -7.45 -5.70 -6.26 --5.78 -3.99 -9.42 -4.18 -4.73 -4.81 -5.37 -5,45 -4.78 -7.74 -5.44 -6.00 -5.86 -5.84
+ 9.30 +11.90 -10.12 + 3.45 - 6.80 -31,40 -39.74 -27.04 -24.83 -21.85 -16.30 -58.92 -22.31 -27.47 -15.26 -44.84 -30.70 -12.15 -58.11 -27.68 -28.59 -16.77 -23.76
+15.38 +24.78 - 3.60 +20.81 +12.64 +10.36 +19.90 +18.58 +25.22 +24.42 +15.62 +16.44 +11.15 +10.37 +23.22 - 1.88 +12.90 +26.09 + 3.81 +15.80 +19.39 +30.14 +22.99
32.00 18.00 20.00 22.62 8.00 36.00 15.47 27.00 25.09 27.07 15.00 34.00 25.77 65.00
-
So So Nw So Nw Nw Nw Nw We So Nw Nw We We So
We Nw We
X Z Y X Y Y X X X Z Y X Y Y X X Y -
2.6- 3.8 3.4- 7.0
2.8-39.6 2.4- 4.1 7.2--16.8 4,4- 2,4
2.0-14.0
2.4-11.4
3.0- 7,4
2.0-20.0 6.6-31.1 2.6- 3.7 2.2- 5.7
E E M,E S,A E S,R S,R,M,A,B,E R.B S,R,M,A,B,E S,R,M,A,B,E E E S,R,M,A,B,E Z S,B,E E S M,A B S,R,A,B,E S,A,B,E S,A,B S,E
1979 1979 1979 1979 1979 1979 1979 1979 1 9 79 1979 1979 1979 1979 1979 1979 1979 1979 1 9 80 1980 1980 1980 1980 19 80 1980 19 80 1980 1 9 80 1980 1980
1 1 2 2 2 3 3 3 3 3 3 11 11 12 12 12 12 1 1 1 1 2 2 2 2 2 3 3 4
22 24 7 9 27 8 9 13 14 26 27 29 30 4 5 6 14 6 22 23 28 14 19 23 24 29 3 14 15
- 5. 2 7 - 4. 5 7 -5.57 - 8 .1 6 - 6 .81 - 3 .3 7 -3.56 -4.66 -4.19 -1.47 -2.12 -3.98 - 3 .1 4 - 6 .2 2 - 3 .4 0 - 4.2 5 - 6 .1 5 - 8 .0 6 -4.77 -6.17 - 2.7 3 - 4 .1 8 -5.87 - 3 .8 3 - 5 .3 6 -4.90 - 4 .79 -5.56 -5.54
- 1 8 .0 7 - 1 5 .9 7 -48 .95 - 7 5.4 6 - 6 0 .2 5 - 1 6 .8 3 - 6.97 - 26 .6 5 -17.86 - 0.08 - 1.68
Nw
+24.1 7 +20.59 - 4 .3 8 -10.1 5 - 5.77 +10 .1 4 + 21 .51 +1 0. 64 +15 .66 +11.6 8 +1 5 .28
We So We So
Nw Nw Nw
-
Nw We 15.00 20.00
Nw Nw So
20.00 14.62 14.77
1 7. 0 0 13.00 34.00
5.0 17.6 4.8 6.7 5.4 16.1 2.7 6.8
7.0 3.8 18.2 10.2 31.0
-
-
-
Nw Nw Nw
Y Y X X X X Z X X Z Y Y Z Y
10.7 18.8 22.0 4.8 8.8 3.6 2.8 6.0 7.4 7.3 3 .3 5 .8 5.7 16.1
We We We So So So So
Nw Nw So 10 .00
Y X X X Z Y y X X X X Y Y Z
Nw
2.4- 7.9
3 .9- 5. 7 5.8- 7.2
11.6-20.6 2.0- 3.3 2.7-1 4. 0
-
3.3-1 7.0
-
2.0- 1 8.7 11.5-27. 6
-
5.6-12.0
-
3. 5- 8.5 2.0-12.7 3. 9- 10 .0
2.0-1 2.0
-
R,M ,A,B E R ,M,B R,M ,B,E S R ,B S,B S,M,B B R R R R,Z,A B R S,Z,M S,R,Z Z B S,M M R R,Z S,Z Z,M,A Z Z S,R ,Z ,A B
*S ee text.
~
........
212 TABLE II Isotopic data by trajectory and by "source"
3H
0"0
oD
d
Trajectory : n So mean (28.9)* SD
13 -5.33 1.44
7 -37.14 19.41
7 + 6.52 9.03
Nw (46.7)
n mean SD
21 -5.14 1.77
13 -23.62 15.94
13 +17.79 8.57
We (24.4)
n mean SD
11 -4.72 1.88
7 -25.70 23.65
7 +15.05 12.14
25.77
Z (15.6)
n mean SD
7 -5.45 0.33
3 -39.71 17.90
3 + 4.99 9.32
2 35.00 1.41
Y (37.7)
n mean SD
17 -4.90 1.27
10 -20.32 9.48
10 +21.77 6.08
9 23.00 16.55
X (46.7)
n mean SD
21 -5.10 2.08
15 -27.97 22.55
15 +10.37 2.40
7 19.97 9.18
6 22.50 11.53
1
Source:
n = number of samples; SD = standard deviation. *The number in parentheses is the frequency of occurrence of the trajectory and source types in percent.
There is a general trend of increasing 8 180 and oD with the zonal index (Fig. 4a and b). There is a significantly high correlation between the tritium content and the zonal index (r = -0.69, n = 17), which means that higher tritium values are associated with low index values, as may be expected in view of the marked north-south gradient of tritium (Lal and Rama, 1966). Such a correlation is very prominent in air masses reaching the region from the south (r = -0.95, n = 6, Fig. 5). This feature indicates the possible use of tritium as a tracer of precipitating air masses by means of an individual storm. The ability to trace European humid air masses, relatively high in 3H, would enable one to differentiate them from proper Mediterranean air masses, much poorer in 3H (Gat and Carmi, 1970). This distinction can also be made by considering a oD-o 18 0 diagram (Fig. 6). The points having a deuterium excess of less than 10 0 / uo are associated with western and southern trajectories, whereas the points with deuterium excesses greater than
213
8 leo %0 a
0 -I
X.
-2
X.
-3
Y. XoY•
~...
-4 y.
-5
x,.\
y.
x,.v"
r
x
x.
':f
x,
7
y y.
Y.x.
Zo'4-~
x+
.
Y.
x
y.
1.,
x
x+
x, z,
y
+
z.
•
x.
12
13
14
15
Tropopause level xl0 3m
20
b
10
o -10
y
-20 -30 -40
y
x'+
x, •
•~
- so x
-60 -70
7
Fig. 3. a. {, 13 0 vs. tropopause level; b. {,D vs, tropopause level (symbols indicate trajectories as follows: • = Nw , + = We, 0 = So; letters (X, Y, Z) indicate "source"}.
22%0 [typical to intensive interaction of cold dry air with the eastern part of the Mediterranean Sea (Gat and Carmi, 1970)], are associated with north to northwest trajectories (Table III).
DISCUSSION
In Fig. 6 it is shown that the isotopic data may be divided into three groups, where the two extreme ones, which are characterized by d > 22%0' oD > -25%0 and d < 10%0' oD < -39%0' respectively, will be discussed in greater detail.
214
8"'0%.
a
-I
-2 -3
/
I I
-4 Zo
Y
-40
-20
x.
lee \ J. \
z·Y·
Y.;x·
y.
Y.
yx.
.z
Y·
x. 120 140 Zonal index
100
80
Y.
x. Y.
Y.
z.
X" y.
Xo
z· x,
20
-20
/)ISO
.x
."4
x-
\x. x. \ x. x. \
Y.
-50
.z
Y
Y·
x-
Y.
/
-60 -70
Fig. 4. a.
\ \
x,
z·
• z. -30 x· y. x. -40 y.
-40
\
20 x· 60 8D"/oo 10 b ,- ,-- ....... -, x. 0 / Ve', Xo / -10 / / Y.
Y.
. x. .y
y~Y.
x" \
Y·
,Xt;"y. Xo
Y·
-7 -8
v. ~fX.
I
z••x -5
t»
'"
/
xo xo·
,
-,
40
60
80
100
120 140 Zonal index
vs. zonal index; b. /)D vs. zonal index (notation as in Fig. 3).
3H 35 30
25
oX
.x
20 15
10
oy
oy
oX oy
.;x.
.x
oy
oy
oy
oX
5
-40 -20
20
40
60
80
100 120 140 Zonal index
Fig. 5. Tritium vs. zonal index (notation as in Fig. 3).
215
80
I
\ .1 Fi g. 6. Weighted means o f 5" 0
VS.
5D (n otat io n as in Fig. 3 ).
TABLE III Frequency distribution of deu terium excess vs. "source" and tr ajectory Y/Nw Y/So %
12 18 %
0 0
Total
d « 12 % < d .;; 18 %
Y/ We X/Nw X/So 3 2
0 0
7 8
1 1
5
2 1 1 4
X/ We Z/Nw Z/So 2 1 2 5
3
3
Z/We To tal 11 5 11 27
It can be seen that the rain storms which are most depleted in the heavy stable isotopes are associated with trajectories approaching the concerned region from the south or from southwest (Fig. 7), whereas the precipitations with a high d-value are associated mostly with air masses coming from the north to northwest (Fig. 8). It was shown (Fig. 3a and b) that there is a general trend of increasing 018 0 and oD with the tropopause level. Hence, precipitation depleted in the stable-isotope content seems to be associated with cold polar air masses.
216
Date - - 29.3.78 --II. 12.78 - - 7. 2.79 9.2.79 --272.79
d - 188 +
381
- 4.38
-10.15 - 5.77
Fig. 7. Trajectories of air masses associated with low deuterium excess (d .;; 10%0)'
The group depleted in the heavy stable isotopes is characterized by air masses which spent at least the last 24 hr. over continental areas (i.e. the northeastern African deserts) before reaching the study area. This may be regarded as an "inland effect" (Dansgaard, 1964). The second group with the contrasting extreme characteristics (i.e. d > 22%0) is characterized by air masses reaching the concerned area from the north-northwest (with the exception of one case) and are associated with a low index flow (Fig. 8). There seems to be some indication that the higher d-values are associated with short, but presumably very intense, interaction between the air mass and the Mediterranean Sea. The shorter the interaction the higher the d-values. This fact needs further investigation also in terms of the intensity of the interaction. As was shown above, the group of samples with high d-values (i.e. d > 22%0) is mostly associated with air masses coming from north to northeast Europe, crossing the Mediterranean Sea in its eastern half and approaching the considered region from west to north. The group of samples with low d-values (i.e. d < 10%0), is associated with air masses coming from the sector confined by northwest and southwest directions and they have a longer trajectory over the North African desert. The intermediate group, to which the majority of cases belong, cannot be defined as clearly with regard to their
217
d "Ioe
DlITE ---- 22.12.77 ..... 23.12.77 -- 13.3.78 24.4. 78 - - 9.1.79 21.1.79 -·-22.179
+25.22 +~.42
23.22 26.09 +30.14 +22.99 +24.17 +
+
Fig. 8. Trajectories of air masses associated with high deuterium excess (d ;;. 22%
0),
trajectories and flow pattern; these seem to be some combination of the two extreme groups mentioned above. The processes which determine the isotopic composition of precipitation are rather complex and obviously cannot be explained by one simple correlation. However, it seems that the history of the air mass and its water vapour plays an important role, as revealed in this study. Further research is needed taking into account other meteorological processes on various scales. ACKNOWLEDGEMENTS
The authors wish to express their thanks to the staff of the Isotope Laboratory of the Weizmann Institute, for analyzing the samples and to the Israel Meteorological Service for assisting them in collecting the rain samples. We wish also to thank the Jacob Blaustein Institute for Desert Research (Ben Gurion University of the Negev) of Sde Boqer and the Physical Geography Department of the Hebrew University, Jerusalem, for their cooperation in supplying facilities for field work. Special thanks to Mr. S. Jaffe of the Israel Meteorological Service for his constructive advice and comments which were of great value to our work. We are also grateful to the Israel National Academy of Science for funding this research.
218
REFERENCES Adar, E., Levin, M. and Barzilai, A, 1980. A hermetic rain sample collector development. Water Resour. Res., 16: 592-596. Barry, R.G. and Perry, A.H., 1973. Synoptic Climatology, Methods and Applications. Methuen, London, 555 pp. Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus, 16: 436-468. Evenari, M., Shanan, L. and Tadmor, N., 1971. The Negev, The Challenge of A Desert. Harvard University Press, Cambridge, Mass., 345 pp. Gagin, A and Neumann, J., 1974. Rain stimulation and cloud physics in Israel. In: W.N. Hess (Editor), Weather and Climate Modification. Wiley, New York, N.Y., pp. 454-494. Gat, J.R., 1981. Paleoclimate conditions in the Levant as revealed by the isotopic composition of paleowaters. Isr. Meteorol. Res. Pap., 3: 13-28. Gat, J.R. and Carmi, I., 1970. Evolution of the isotopic composition of atmospheric water in the Mediterranean Sea area. J. Geophys. Res., 75: 3039-3048. Gat, J.R. and Issar, A., 1974. Desert isotope hydrology, water resources of the Sinai Desert. Geochim. Cosmochim. Acta, 38: 1117-1131. Hage, K.D., Gray, J. and Linton, J.C., 1975. Isotopes in precipitation in northwestern North America. Mon. Weather Rev., 103: 958-966. I.AE.A. (International Atomic Energy Agency), 1981. Statistical treatment of environmental isotope data in precipitation. Int. At. Energy Agency, Vienna, Tech. Rep, Ser. No. 206. IM.S. (Israel Meteorological Services), 1977. Average Annual Rainfall Map. Isr. Meteorol. Serv., Bet Dagan. Lal, D. and Rama, 1966. Characterization of global tropospheric mixing based on man made 14C,3H and 9 0 Sr . J. Geophys. Res., 71: 2865-2873. Levin, M., Gat, J.R. and Issar, A., 1980. Precipitation, flood and groundwaters of the Negev highlands: an isotopic study of the desert hydrology. Proc. Adv. Group Meet., Arid-Zone Hydrology, Investigations with Isotope Techniques, Int. At. Energy Agency (I.A.E.A.), Vienna, pp. 3-22. Yurtsever, Y., 1975. Worldwide survey of stable. isotopes in precipitation. Int. At. Energy Agency (I.A.E.A.), Vienna, Inter. Rep.
205
THE RELATION BETWEEN THE 18 0 AND DEUfERIUM CONTENTS OF RAIN WATER IN THE NEGEV DESERT AND AIR-MASS TRAJECTORIES
CLAUDE LEGUY', MICHAEL RINDSBERGER 2,3 A. ZANGWIL', ARIE ISSAR' and JOEL R. GAT3 '
"Jacob Blaustein Institute for Desert Research and Geological Department Ben Gurion University of the Negev, Beer-Sheua (Israel) 'Israel Meteorological Service, Bet Dagan (Israel) 'Department of Isotope Research, The Weizmann Institute of Science, Rehovot (Israel) (Received November 15, 1982; revised and accepted May 17, 1983)
ABSTRACT Leguy, C1., Rindsberger, M., Zangwil, A., Issar, A. and Gat, J.R., 1983. The relation between the 18 0 and deuterium contents of rain water in the Negev Desert and air-mass trajectories. Isot. Geosci., 1: 205-218. Sampling of rain water was carried out in the Negev, Israel, from 1978 till 1981, by means of a self-sealing sampler which enables the sampling of each separate rain storm, as well as parts of each storm. The relation between the isotopic composition and various synoptic parameters is discussed. Based on "deuterium excess" values, the rain samples can be separated into three groups. The majority of the samples have a "deuterium excess" between 10 and 22%°' These samples have different histories from the meteorological point of view. However, there are two extreme groups, one has "deuterium excess" values above 22%0 and the other has values less than 10%0' It was found that the rains which are most depleted with regard to deuterium and with the lowest "deuterium excess" values are associated with air masses that reach the region concerned from the southwest. Rains with a "deuterium excess" of more than 22%0 are associated with air masses which come mainly from northeastern Europe and reach the considered region from west to northwest, following intense interaction with the central-eastern Mediterranean Sea.
INTRODUCTION
The Negev forms the southern arid half of Israel. The average annual precipitation over most of this area is less than 200 mm (Fig. 1b) (I.M.S., 1977). The Negev forms part of the desert belt extending from the Sahara through Cyrenaica, Egypt, and the Sinai to the Arabian Desert. Owing to its location close to the southeastern Mediterranean coast, it is relatively more affected by the winter cyclonic region of the Mediterranean Sea than the deserts of eastern North Africa (Evenari et al., 1971).
0167-6695/83/$03.00
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1983 Elsevier Science Publishers B.V.
206
The Mediterranean winter precipitation in the Levant shows, on the average, a distinctive isotopic character with a relatively large excess of the d parameter* (Gat and Carmi, 1970). The influence of the Mediterranean regime can also be traced in the meteoric waters of the Negev and Sinai deserts by the contents of 18 0 and deuterium (Gat and Issar, 1974). On the other hand, comparison of data from the more humid northern part of the country with some major storms in the Negev, shows more depleted isotopic values than expected in the latter (Levin et al., 1980). In contrast to the abovementioned cases, one also occasionally encounters rains which are enriched in the heavy isotopic species. These rains have a very low tritium content and their origin has been related to air masses coming from the Indian Ocean. In this study, ·some synoptic aspects are considered with regard to the isotopic composition of rain . Any such relationship might also throw additional light on the climate of this region at the time that the paleowaters of this region were formed (recharged). It has been noted that the isotopic composition of the Sinai and the Negev paleowaters (average values 5 18 0 = -6.95%o, oD = -49%0, d = 7% 0) (Gat, 1981), is distinct from the mean composition of meteoric waters of the Mediterranean cyclonic regime (018 0 = -5.57%0; oD = -22.9%0' Bet Dagan) (I.A.E.A., 1981). ISOTOPIC DATA
The isotopic data set, discussed in this study, consists of ~ 150 samples taken at Avdat (A), Beer-Sheva (B), Sde Boqer (S), Sadot (E), Mizpeh Ramon (M) and Revivim (R ), as reported by Levin et al. (1980). This data set has been supplemented by recent measurements taken at the above-mentioned locations and, in addition, at Zavoa (Z). These seven stations are distributed throughout the central Negev (Fig. 1b). At three of the stations (R , Z, S) a multiple rain sampler (Adar et al., 1980) was used. In this sampler, once the collection flask contains 500 em" of water, representing 2 mm of rain, it is sealed hermetically and an overflow mechanism enables any succeeding amount of rain to be sampled, up to a total of 12 mm. At the other stations, rain-water samples were collected from standard Israel Meteorological Service rain recorders. Analyses for the isotopic composition of the water samples esO, D and tritium) were performed at the Isotope Laboratory of the Weizmann Institute of Science. 18 0 and deuterium are reported in 0 (%0) units relative to SMOW in the accepted manner. Tritium is reported in tritium units (TV). The average reproducibility of the stable-isotopes measurements was ± 0.15%0 for 0 18 0 and % ± 1.5 0 for oD; the error of estimate of the derived quantity d is then of the order of ± 2.7%0' The original data set consisted of '" 150 samples. However, preliminary isotope analysis showed that the isotopic data of rain events with amounts of *d , the deuterium excess, is defined as d = c5 D-8c5 18 0 ; the d-value is established in the atmospheric part of the water cycle in the source areas of the vapour.
207
a
a.
o
extremly arid
~ arid
I""o'd semi-arid b.
station elevation
/{p isohyet [1 J
28"
34"
35"
Fig . 1. Location of study area: (a) general context map of arid zones; and (b) rainfallcollecting stations in the Negev Highlands.
rain less than 2 mm were rather erratic. The isotopic composition of lowintensity rains is possibly distorted by the fractionation which accompanies the evaporation of the falling rain drops. Hence, in our study we considered only those events in which the rain amount was equal to or greater than 2 mm. It was found, also, that the mean scatter range of values from the various collection stations on any given rain day (an order of ± 1%0 in 8180) was significantly less than the scatter of the daily averages from different rain days (an order of ± 2%0 in 8180). Considering a large-scale pattern, we may assume that rain events, on any particular day, are affected by the same synoptic conditions. Therefore, it seems justified to discuss these data on the basis of the weighted mean isotopic composition for each precipitation event (rain day). For each event their amount-weighted means of the isotopic composition were calculated for all the measurements taken on the same day: n
8%0 (weighted) = 1/P~8iPi 1
208
where Pi = daily amount of rain at station i; (if Pi (precipitation) > 2 mm); p = ~~ Pi; and n = number of stations considered (1 up to 7). The calculated weighted means are given in Table 1. The span of the isotopic composition data for the different rain days is rather wide and ranges from - -8 to -1%0 for li 18 0 and -75 to -10%0 in liD. No systematic amount-effect could be observed in this data set. The li18 0 _ and liD-values are, however, rather well correlated along meteoric water lines, with ~ 80% of the data showing a deuterium excess of between +10 and +30%°' d = +15%0 on the average. METEOROLOGICAL DATA
For the synoptic meteorological analysis, we used surface and 700-mbar synoptic charts and upper air measurements taken at Bet Dagan, Israel, which is situated - 100 km north of the region considered. These measurements include the tropopause level, the temperature and relative humidity at various other levels. Air-mass trajectory characterization is based on 700-mbar synoptic charts for the three days preceding the rain event. The general flow is characterized by the so-called "zonal index". The index has been calculated between Cairo, Egypt (62,378) and Ankara, Turkey (17,130), from the 700-mbar chart. It should be kept in mind that a high index indicates a tendency toward zonal flow, whereas a low index represents a tendency toward meridional flow, positive when the pressure increases southward and negative when the pressure decreases southward. Applying the method suggested by Barry and Perry (1973), air-mass trajectories were determined, based on 700-mbar charts. The trajectories were classified as follows (Gagin and Neumann, 1974): We trajectory, represents trajectories whose main direction is from west and whose air masses travelled most of the time over the Mediterranean Sea. Nw trajectory, represents trajectories whose main direction is from north to northwest, and whose air masses travelled most of the time over the European continent. So trajectory, when the main direction is from the south, and the air masses travelled most of the time over the African continent. It should be mentioned that Gagin and Neumann's (1974) analysis includes also another type of trajectory. However, in the sample under study this type has not been associated with any of the rain events in the considered region. A "source" term is defined as the region in which the air mass was located 72 hr. before reaching the Negev Highlands. We classified the "sources" into three categories as follows: Source X - West Europe and the Atlantic Source Y - north of Central and East Europe Source Z - the south, mainly Africa
209
Examples of the different types of trajectories under study are shown in Fig. 2.
~ --- ~
24: day OOH. recording GMT 12H. recording GMT intermediate time Nw trajectory _ ._.- We trajectory ------ So trajectory (NEGEV RAINFALL from 24.2.78;12.1278;2.1. c
•
IOf
Fig . 2. Trajectories types, based on 700-mbar synoptic charts.
RESULTS
The frequency of occurrence of the various trajectories in the present study, together with a summary of some statistical parameters sorted according to trajectory type and "source", is given in Table II. It seems that on the average the southern trajectory may be characterized by rains which are often depleted in the heavy stable isotopes, with significantly lower "deuterium excess" values in comparison to the other trajectories. Yurtsever (1975) found a rather high correlation between the mean monthly b 180 -values and the mean monthly surface temperature at some stations. Hage et al. (1975) found a high correlation between mean annual b 180-values and mean annual 800-mbar temperatures. In our study, which refers to individual storms, no such high correlation was found. However, there seems to be a trend of increasing values of b 180 and bD with the tropopause level (Fig. 3a and b), with correlation coefficients 0.51 and 0.56, respectively . This may indicate a dependence of isotopic composition on the air-mass temperature, as the tropopause level is strongly correlated with the mean temperature of the tropospheric air column.
t.:l I-'
o
TABLE I Isotopic composition ofrain in the Negev, 1977-1980 Year
Month
Day
6'
10
(%0)
6D (%0)
d (%0)
Tritium content
Trajectory*
Source*
Average Range of Stations* precipitation precipitation (mm) (mm)
-
-
3.2 3.9 3.2 5.2 7.1 5.1 12.9 3.3 13.6 7.7 4.6 2.8 9.2 6.0 7.9 4.1 4.3 5.2 2.2 19.9 16.7 3.1 3.9
(T.V.)
1977 1977 1977 1977 1977 1977 1977 1977 1977 1977 1978 1978 1978 1978 1978 1978 1978 1978 1978 1978 1979 1979 1979
10 11 11 11
12 12 12 12 12 12 1 1 2 2 3 3 3 4 12 12 1 1 1
29 2 11
12 6 12 14 21 22 23 2 3 23 28 13 29 30 24 11 12 8 9 21
-0.76 -1.61 -0.82 -2.17 -2.43 -5.27 -7.45 -5.70 -6.26 --5.78 -3.99 -9.42 -4.18 -4.73 -4.81 -5.37 -5,45 -4.78 -7.74 -5.44 -6.00 -5.86 -5.84
+ 9.30 +11.90 -10.12 + 3.45 - 6.80 -31,40 -39.74 -27.04 -24.83 -21.85 -16.30 -58.92 -22.31 -27.47 -15.26 -44.84 -30.70 -12.15 -58.11 -27.68 -28.59 -16.77 -23.76
+15.38 +24.78 - 3.60 +20.81 +12.64 +10.36 +19.90 +18.58 +25.22 +24.42 +15.62 +16.44 +11.15 +10.37 +23.22 - 1.88 +12.90 +26.09 + 3.81 +15.80 +19.39 +30.14 +22.99
32.00 18.00 20.00 22.62 8.00 36.00 15.47 27.00 25.09 27.07 15.00 34.00 25.77 65.00
-
So So Nw So Nw Nw Nw Nw We So Nw Nw We We So
We Nw We
X Z Y X Y Y X X X Z Y X Y Y X X Y -
2.6- 3.8 3.4- 7.0
2.8-39.6 2.4- 4.1 7.2--16.8 4,4- 2,4
2.0-14.0
2.4-11.4
3.0- 7,4
2.0-20.0 6.6-31.1 2.6- 3.7 2.2- 5.7
E E M,E S,A E S,R S,R,M,A,B,E R.B S,R,M,A,B,E S,R,M,A,B,E E E S,R,M,A,B,E Z S,B,E E S M,A B S,R,A,B,E S,A,B,E S,A,B S,E
1979 1979 1979 1979 1979 1979 1979 1979 1 9 79 1979 1979 1979 1979 1979 1979 1979 1979 1 9 80 1980 1980 1980 1980 19 80 1980 19 80 1980 1 9 80 1980 1980
1 1 2 2 2 3 3 3 3 3 3 11 11 12 12 12 12 1 1 1 1 2 2 2 2 2 3 3 4
22 24 7 9 27 8 9 13 14 26 27 29 30 4 5 6 14 6 22 23 28 14 19 23 24 29 3 14 15
- 5. 2 7 - 4. 5 7 -5.57 - 8 .1 6 - 6 .81 - 3 .3 7 -3.56 -4.66 -4.19 -1.47 -2.12 -3.98 - 3 .1 4 - 6 .2 2 - 3 .4 0 - 4.2 5 - 6 .1 5 - 8 .0 6 -4.77 -6.17 - 2.7 3 - 4 .1 8 -5.87 - 3 .8 3 - 5 .3 6 -4.90 - 4 .79 -5.56 -5.54
- 1 8 .0 7 - 1 5 .9 7 -48 .95 - 7 5.4 6 - 6 0 .2 5 - 1 6 .8 3 - 6.97 - 26 .6 5 -17.86 - 0.08 - 1.68
Nw
+24.1 7 +20.59 - 4 .3 8 -10.1 5 - 5.77 +10 .1 4 + 21 .51 +1 0. 64 +15 .66 +11.6 8 +1 5 .28
We So We So
Nw Nw Nw
-
Nw We 15.00 20.00
Nw Nw So
20.00 14.62 14.77
1 7. 0 0 13.00 34.00
5.0 17.6 4.8 6.7 5.4 16.1 2.7 6.8
7.0 3.8 18.2 10.2 31.0
-
-
-
Nw Nw Nw
Y Y X X X X Z X X Z Y Y Z Y
10.7 18.8 22.0 4.8 8.8 3.6 2.8 6.0 7.4 7.3 3 .3 5 .8 5.7 16.1
We We We So So So So
Nw Nw So 10 .00
Y X X X Z Y y X X X X Y Y Z
Nw
2.4- 7.9
3 .9- 5. 7 5.8- 7.2
11.6-20.6 2.0- 3.3 2.7-1 4. 0
-
3.3-1 7.0
-
2.0- 1 8.7 11.5-27. 6
-
5.6-12.0
-
3. 5- 8.5 2.0-12.7 3. 9- 10 .0
2.0-1 2.0
-
R,M ,A,B E R ,M,B R,M ,B,E S R ,B S,B S,M,B B R R R R,Z,A B R S,Z,M S,R,Z Z B S,M M R R,Z S,Z Z,M,A Z Z S,R ,Z ,A B
*S ee text.
~
........
212 TABLE II Isotopic data by trajectory and by "source"
3H
0"0
oD
d
Trajectory : n So mean (28.9)* SD
13 -5.33 1.44
7 -37.14 19.41
7 + 6.52 9.03
Nw (46.7)
n mean SD
21 -5.14 1.77
13 -23.62 15.94
13 +17.79 8.57
We (24.4)
n mean SD
11 -4.72 1.88
7 -25.70 23.65
7 +15.05 12.14
25.77
Z (15.6)
n mean SD
7 -5.45 0.33
3 -39.71 17.90
3 + 4.99 9.32
2 35.00 1.41
Y (37.7)
n mean SD
17 -4.90 1.27
10 -20.32 9.48
10 +21.77 6.08
9 23.00 16.55
X (46.7)
n mean SD
21 -5.10 2.08
15 -27.97 22.55
15 +10.37 2.40
7 19.97 9.18
6 22.50 11.53
1
Source:
n = number of samples; SD = standard deviation. *The number in parentheses is the frequency of occurrence of the trajectory and source types in percent.
There is a general trend of increasing 8 180 and oD with the zonal index (Fig. 4a and b). There is a significantly high correlation between the tritium content and the zonal index (r = -0.69, n = 17), which means that higher tritium values are associated with low index values, as may be expected in view of the marked north-south gradient of tritium (Lal and Rama, 1966). Such a correlation is very prominent in air masses reaching the region from the south (r = -0.95, n = 6, Fig. 5). This feature indicates the possible use of tritium as a tracer of precipitating air masses by means of an individual storm. The ability to trace European humid air masses, relatively high in 3H, would enable one to differentiate them from proper Mediterranean air masses, much poorer in 3H (Gat and Carmi, 1970). This distinction can also be made by considering a oD-o 18 0 diagram (Fig. 6). The points having a deuterium excess of less than 10 0 / uo are associated with western and southern trajectories, whereas the points with deuterium excesses greater than
213
8 leo %0 a
0 -I
X.
-2
X.
-3
Y. XoY•
~...
-4 y.
-5
x,.\
y.
x,.v"
r
x
x.
':f
x,
7
y y.
Y.x.
Zo'4-~
x+
.
Y.
x
y.
1.,
x
x+
x, z,
y
+
z.
•
x.
12
13
14
15
Tropopause level xl0 3m
20
b
10
o -10
y
-20 -30 -40
y
x'+
x, •
•~
- so x
-60 -70
7
Fig. 3. a. {, 13 0 vs. tropopause level; b. {,D vs, tropopause level (symbols indicate trajectories as follows: • = Nw , + = We, 0 = So; letters (X, Y, Z) indicate "source"}.
22%0 [typical to intensive interaction of cold dry air with the eastern part of the Mediterranean Sea (Gat and Carmi, 1970)], are associated with north to northwest trajectories (Table III).
DISCUSSION
In Fig. 6 it is shown that the isotopic data may be divided into three groups, where the two extreme ones, which are characterized by d > 22%0' oD > -25%0 and d < 10%0' oD < -39%0' respectively, will be discussed in greater detail.
214
8"'0%.
a
-I
-2 -3
/
I I
-4 Zo
Y
-40
-20
x.
lee \ J. \
z·Y·
Y.;x·
y.
Y.
yx.
.z
Y·
x. 120 140 Zonal index
100
80
Y.
x. Y.
Y.
z.
X" y.
Xo
z· x,
20
-20
/)ISO
.x
."4
x-
\x. x. \ x. x. \
Y.
-50
.z
Y
Y·
x-
Y.
/
-60 -70
Fig. 4. a.
\ \
x,
z·
• z. -30 x· y. x. -40 y.
-40
\
20 x· 60 8D"/oo 10 b ,- ,-- ....... -, x. 0 / Ve', Xo / -10 / / Y.
Y.
. x. .y
y~Y.
x" \
Y·
,Xt;"y. Xo
Y·
-7 -8
v. ~fX.
I
z••x -5
t»
'"
/
xo xo·
,
-,
40
60
80
100
120 140 Zonal index
vs. zonal index; b. /)D vs. zonal index (notation as in Fig. 3).
3H 35 30
25
oX
.x
20 15
10
oy
oy
oX oy
.;x.
.x
oy
oy
oy
oX
5
-40 -20
20
40
60
80
100 120 140 Zonal index
Fig. 5. Tritium vs. zonal index (notation as in Fig. 3).
215
80
I
\ .1 Fi g. 6. Weighted means o f 5" 0
VS.
5D (n otat io n as in Fig. 3 ).
TABLE III Frequency distribution of deu terium excess vs. "source" and tr ajectory Y/Nw Y/So %
12 18 %
0 0
Total
d « 12 % < d .;; 18 %
Y/ We X/Nw X/So 3 2
0 0
7 8
1 1
5
2 1 1 4
X/ We Z/Nw Z/So 2 1 2 5
3
3
Z/We To tal 11 5 11 27
It can be seen that the rain storms which are most depleted in the heavy stable isotopes are associated with trajectories approaching the concerned region from the south or from southwest (Fig. 7), whereas the precipitations with a high d-value are associated mostly with air masses coming from the north to northwest (Fig. 8). It was shown (Fig. 3a and b) that there is a general trend of increasing 018 0 and oD with the tropopause level. Hence, precipitation depleted in the stable-isotope content seems to be associated with cold polar air masses.
216
Date - - 29.3.78 --II. 12.78 - - 7. 2.79 9.2.79 --272.79
d - 188 +
381
- 4.38
-10.15 - 5.77
Fig. 7. Trajectories of air masses associated with low deuterium excess (d .;; 10%0)'
The group depleted in the heavy stable isotopes is characterized by air masses which spent at least the last 24 hr. over continental areas (i.e. the northeastern African deserts) before reaching the study area. This may be regarded as an "inland effect" (Dansgaard, 1964). The second group with the contrasting extreme characteristics (i.e. d > 22%0) is characterized by air masses reaching the concerned area from the north-northwest (with the exception of one case) and are associated with a low index flow (Fig. 8). There seems to be some indication that the higher d-values are associated with short, but presumably very intense, interaction between the air mass and the Mediterranean Sea. The shorter the interaction the higher the d-values. This fact needs further investigation also in terms of the intensity of the interaction. As was shown above, the group of samples with high d-values (i.e. d > 22%0) is mostly associated with air masses coming from north to northeast Europe, crossing the Mediterranean Sea in its eastern half and approaching the considered region from west to north. The group of samples with low d-values (i.e. d < 10%0), is associated with air masses coming from the sector confined by northwest and southwest directions and they have a longer trajectory over the North African desert. The intermediate group, to which the majority of cases belong, cannot be defined as clearly with regard to their
217
d "Ioe
DlITE ---- 22.12.77 ..... 23.12.77 -- 13.3.78 24.4. 78 - - 9.1.79 21.1.79 -·-22.179
+25.22 +~.42
23.22 26.09 +30.14 +22.99 +24.17 +
+
Fig. 8. Trajectories of air masses associated with high deuterium excess (d ;;. 22%
0),
trajectories and flow pattern; these seem to be some combination of the two extreme groups mentioned above. The processes which determine the isotopic composition of precipitation are rather complex and obviously cannot be explained by one simple correlation. However, it seems that the history of the air mass and its water vapour plays an important role, as revealed in this study. Further research is needed taking into account other meteorological processes on various scales. ACKNOWLEDGEMENTS
The authors wish to express their thanks to the staff of the Isotope Laboratory of the Weizmann Institute, for analyzing the samples and to the Israel Meteorological Service for assisting them in collecting the rain samples. We wish also to thank the Jacob Blaustein Institute for Desert Research (Ben Gurion University of the Negev) of Sde Boqer and the Physical Geography Department of the Hebrew University, Jerusalem, for their cooperation in supplying facilities for field work. Special thanks to Mr. S. Jaffe of the Israel Meteorological Service for his constructive advice and comments which were of great value to our work. We are also grateful to the Israel National Academy of Science for funding this research.
218
REFERENCES Adar, E., Levin, M. and Barzilai, A, 1980. A hermetic rain sample collector development. Water Resour. Res., 16: 592-596. Barry, R.G. and Perry, A.H., 1973. Synoptic Climatology, Methods and Applications. Methuen, London, 555 pp. Dansgaard, W., 1964. Stable isotopes in precipitation. Tellus, 16: 436-468. Evenari, M., Shanan, L. and Tadmor, N., 1971. The Negev, The Challenge of A Desert. Harvard University Press, Cambridge, Mass., 345 pp. Gagin, A and Neumann, J., 1974. Rain stimulation and cloud physics in Israel. In: W.N. Hess (Editor), Weather and Climate Modification. Wiley, New York, N.Y., pp. 454-494. Gat, J.R., 1981. Paleoclimate conditions in the Levant as revealed by the isotopic composition of paleowaters. Isr. Meteorol. Res. Pap., 3: 13-28. Gat, J.R. and Carmi, I., 1970. Evolution of the isotopic composition of atmospheric water in the Mediterranean Sea area. J. Geophys. Res., 75: 3039-3048. Gat, J.R. and Issar, A., 1974. Desert isotope hydrology, water resources of the Sinai Desert. Geochim. Cosmochim. Acta, 38: 1117-1131. Hage, K.D., Gray, J. and Linton, J.C., 1975. Isotopes in precipitation in northwestern North America. Mon. Weather Rev., 103: 958-966. I.AE.A. (International Atomic Energy Agency), 1981. Statistical treatment of environmental isotope data in precipitation. Int. At. Energy Agency, Vienna, Tech. Rep, Ser. No. 206. IM.S. (Israel Meteorological Services), 1977. Average Annual Rainfall Map. Isr. Meteorol. Serv., Bet Dagan. Lal, D. and Rama, 1966. Characterization of global tropospheric mixing based on man made 14C,3H and 9 0 Sr . J. Geophys. Res., 71: 2865-2873. Levin, M., Gat, J.R. and Issar, A., 1980. Precipitation, flood and groundwaters of the Negev highlands: an isotopic study of the desert hydrology. Proc. Adv. Group Meet., Arid-Zone Hydrology, Investigations with Isotope Techniques, Int. At. Energy Agency (I.A.E.A.), Vienna, pp. 3-22. Yurtsever, Y., 1975. Worldwide survey of stable. isotopes in precipitation. Int. At. Energy Agency (I.A.E.A.), Vienna, Inter. Rep.