Global warming impact on the dominant precipitation processes in the Middle East
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In this study, the ability of a regional climate model, based on MM5, to simulate the climate of the Middle East at the beginning of the twenty-first century is assessed. The model is then used to simulate the changes due to global warming over the twenty-first century. The regional climate model displays a negative bias in temperature throughout the year and over most of the domain. It does a good job of simulating the precipitation for most of the domain, though it performs relatively poorly over the southeast Black Sea and southwest Caspian Sea. Using boundary conditions obtained from CCSM3, the model was run for the first and last 5 years of the twenty-first century. The results show widespread warming, with a maximum of ~10 K in interior Iran during summer. It also found some cooling in the southeast Black Sea region during spring and summer that is related to increases in snowfall in the region, a longer snowmelt season, and generally higher soil moisture and latent heating through the summer. The results also show widespread decreases in precipitation over the eastern Mediterranean and Turkey. Precipitation increases were found over the southeast Black Sea, southwest Caspian Sea, and Zagros mountain regions during all seasons except summer, while the Saudi desert region receives increases during summer and autumn. Changes in the dominant precipitation-triggering mechanisms were also investigated. The general trend in the dominant mechanism reflects a change away from the direct dependence on storm tracks and towards greater precipitation triggering by upslope flow of moist air masses. The increase in precipitation in the Saudi desert region is triggered by changes in atmospheric stability brought about by the intrusion of the intertropical convergence zone into the southernmost portion of the domain.
KeywordsRoot Mean Square Error Regional Climate Model Storm Track Anomaly Correlation Regional Climate Model Simulation
I would like to thank Oak Ridge National Lab (ORNL), in particular Dr. David Erickson, for making the CCSM3 data available for the creation of boundary conditions for MM5. I acknowledge the modeling groups for providing their data for analysis, the Program for Climate Model Diagnosis and Intercomparison (PCMDI) for collecting and archiving the model output, and the JSC/CLIVAR Working Group on Coupled Modelling (WGCM) for organizing the model data analysis activity. The multi-model data archive is supported by the Office of Science, US Department of Energy and made available through the Earth System Grid. The National Center for Atmospheric Research (NCAR) supplied the NCEP/NCAR reanalysis data and computing capacity to perform the MM5 runs. I also thank members of the SWAP team at Yale University: Ron Smith; Roland Geerken; Frank Hole; and Larry Bonneau for continuing fruitful discussions. This study was carried out as part of the research project “The Water Cycle of the Tigris–Euphrates Watershed: Natural Processes and Human Impacts.” (NNG05GB36G) supported and financed by NASA.
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