The Impact of Urban Structure Changes on the Airflow Speed Circulation in Historic Karbala, Iraq

This study investigates a dynamic air flow circulation in the urban historic structures of Karbala, which is one of the typical examples of historic nuclei in Iraq as well as the Middle Eastern region. The mechanism of natural urban ventilation system of the city is continuously facing forces of change for different reasons, such as socioeconomic, political, and environmental. These changes in the city form included but not limited to: large parts of urban historic structures have been removed and new concrete structures and modern streets, that have different geometry, dimensions, and materials, have been added. Such changes affect a the pattern of street networks and the mass-void proportions in the old urban structures, which were built in efficiency providing ventilation and cooling naturally, and could have great impact on the speed and behavior of the air flow circulation. For the analysis purposes, two phases which are remarkable in forming the old structure of Karbala have been selected and digitized. These phases include the organic urban structures before the initial acts of road building in the beginning of the previous century, before British mandate in 1920, as well as the new comprehensive master plan that was carried out for the city during 1990s, after the end of the Gulf War II. The study area was strictly defined to represent traditional environment relied on using natural ventilation system. Four simulation models of the study area have been created for the aforementioned phases. The first set has shown the air flow speed, while the second set has presented LMA, i.e. the local mean age. The simulation process was supported by surveyed and historic meteorological data. Results show that the changes of old urban structures affect the air flow circulation speed significantly, but more importantly, these results offer a useful source for contemporary urban planning, using comprehensive plans, in historic nuclei with similar characteristics to Karbala in both local and regional areas. One significant limitation of this study, however, is that it has not involved single urban blocks or residential units in the analysis.