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GCM outputs Analysis of global warming over the eastern Mediterranean

PI: Alpert Pinhas
Institution: Tel- Aviv University, Israel
Additional Investigators: Hirsch Tali
Abstract:
Global warming is the result of increasing greenhouse gases concentrations. It is linked with the increasing trend of daily rainfall amounts due to the increased atmospheric water vapor and increasing trend of the surface temperature. The Global Circulation Models (GCM) are used as a tool to simulate climate changes in rainfall and temperatures in response to anthropogenic greenhouse forcing. In previous studies, preliminary evaluation of GCM, 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 on 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 totals 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 the increasing of 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 results 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 to 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.
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