The Importance of the Zagros Mountains Barrier Jet to Future Precipitation in the Fertile Crescent.

This study quantifies the significance of southerly water vapour fluxes, associated with the Zagros Mountains barrier jet, on precipitation occurring in the Eastern Fertile Crescent region and its change due to global warming. Precipitation events are simulated using a Regional Climate Model (MM5-Noah) driven by boundary conditions from a CCSM global climate model simulation with the SRES A2 emission scenario. The precipitation events were grouped into classes based on the similarity of their water vapour fluxes. Results show a massive increase in the southerly dominated classes which are associated with the formation of a barrier jet on the western slopes of the Zagros Mountains. This increase was related to an increase in atmospheric water vapour in the southern portion of the domain rather than to an increase in the frequency of formation or wind speed of the barrier jet itself. The presence of this barrier jet becomes increasingly important to precipitation in the Eastern Fertile Crescent region as global warming progresses. Thus, low resolution models that are unable to capture this phenomena will produce questionable future projections for this region.

Figure 3: Time series of the water vapour flux entering the Fertile Crescent box from the south for classes 4 (a) and 6 (b). Vertical cross section of the water vapour flux crossing the South side of the Fertile Crescent box, 3 hours before the precipitation peak for classes 4 and(c-h) (topography is shown in white).