Analysis of Global Warming over the Eastern Mediterranean

Alpert Pinhas and Hirsch Tali

Department of Geophysics and Planetary Sciences, Tel- Aviv University, Israel

E-mails: pinhas@cyclone.tau.ac.il, tali@vortex.tau.ac.il

 

 

Global warming is the result of increasing greenhouse gases concentrations. It is linked with the increasing trend of daily rainfall amounts due to increased atmospheric water vapor and increasing surface temperature. Global Circulation Models (GCMs) are used as a tool to simulate climate changes in rainfall and temperature in response to anthropogenic greenhouse forcing. In previous studies, preliminary evaluation of GCMs over the eastern Mediterranean region was used as an input for estimating changes in local processes affecting the water balance in the region (Segal et.al, 1994).

 

Recent studies of rainfall trends in the Mediterranean basin have pointed to a paradoxical increase of extreme rainfall in spite of decrease in the totals, as shown by Alpert et al. (2002) for stations in Italy and Spain. This trend was observed over most parts of Israel excluding the south-central and south (the semi-arid zone) which show an opposite trend of increase in total rainfall amounts. The exception of the semi-arid Israeli belt from the regional trend was linked to the effect of large modifications in land use, partly resulting from the connection of southern Israel to the national water carrier in 1964 (Ben-Gai, et. al., 1993, 1998). Furthermore, a positive link was found between land use changes and the enhancement of thermal convection and induced rainfall (Perlin & Alpert, 2001). Another explanation is the increase in the frequency of sub-tropical anti-cyclones, particularly over the western and central Mediterranean (Alpert et al., 2002), and according to NCEP/NCAR reanalysis for the period 1958 - 1998, a southward transition of low-pressure anomalies in the second half of the 20th century over the eastern Mediterranean. During the 90's a center of low-pressure anomaly moved over southern Israel.

 

A very recent study has shown increasing red sea trough events, which affect the rainfall events in the southern part of Israel (Alpert et al, 2002). Temperature analysis of daily maximum and minimum temperatures from 40 stations in Israel revealed that the frequency of occurrence of extreme temperature events, with lower winter and higher summer temperatures, has increased (Ben-Gai et al, 1999). Both observations and modeling studies indicate fewer rainy days and extreme rainfall and temperatures events possibly as a result of global warming.

 

Due to its location bordering the semi-arid zone and encompassing opposite rainfall trends in its northern and southern parts, Israel represents a complex and exceptional climate change behavior.  Therefore, we wish to study the results of several GCMs, to investigate their ability to simulate the climate over the eastern Mediterranean region and to analyze the simulated greenhouse gas induced changes in temperature and precipitation in this area. The suitable data for this purpose would be global sets of monthly means of the available parameters.

References

 

1.      Alpert P, Ben-gai T, Baharad A, Benjamini Y, Yekutieli D, Colacino M, Diodato L, Ramis C, Homar V, Romero R, Michaelides S. and Manes A, 2002, The paradoxical increase of Mediterranean extreme daily rainfall in spite of decrease in total values, Geophysical Research Letters, 29, 11, 31-1 - 31-4,  (June issue).

2.      Alpert P., Osetinsky I., Ziv B., Shafir H., 2002, Trends in Objectively-Classified Eastern Mediterranean Synoptic Systems, 1948-2000, (submitted).

3.      Ben-Gai T, Bitan A, Manes A, Alpert P, Rubin S, 1999, Temporal and spatial trends of temperature patterns in Israel, Theoretical and applied climatology, 64 (3-4): 163-177

4.      Ben-Gai T, Bitan A, Manes A, Alpert P, Rubin S, 1998 Spatial and temporal changes in rainfall frequency distribution patterns in Israel, Theoretical and applied climatology, 61 (3-4): 177 -190.

5.      Ben-Gai T, Bitan A, Manes A, Alpert P, Israeli A, 1998, Aircraft measurements of surface albedo in relation to climatic changes in southern Israel, Theoretical and applied climatology, 61 (3-4): 207-215.

6.      Ben-Gai T, Bitan A, Manes A, Alpert P, 1993, Long-term change in October rainfall patterns in southern Israel, Theoretical and applied climatology, 46 (4): 209-217.

7.      Perlin N, Alpert P, 2001, Effects of land-use modification on potential increase of convection: A numerical mesoscale study over south Israel, Journal of geophysical research- atmosphere, 106 (D19): 22621-22634.

8.      Segal M, Alpert P, Stein U, Mandel M, Mitchell MJ, 1994, Some Assessments of the potential 2 X CO2 climatic effects on Water Balance Components in The Eastern Mediterranean, Climatic Change, 27 (4): 351-371.