Atmospheric circulation types in Marmara Region (NW Turkey) and their influence on precipitation

In this study, circulation types, their long-term mean occurrence frequencies and relationships with precipitation are investigated for the region Marmara, which is the most populated, agriculturally developed and industrialized area in Turkey. Automated Lamb Weather Types classification method is applied on NCEP/NCAR daily mean sea level pressure data to determine the circulation types. Northeasterly (NE) and easterly (E) types are found to be the most frequent both on the annual basis and during winter (DJF, the wettest season in the region). Circulation types with the highest rainfall potential, namely the cyclonic (C) and the northerly (N), are among the least frequent; therefore they are not the dominant 'rainfall modes'. Instead, NE and E have the greatest contribution to the regionally averaged rainfall amount, although they do not have the highest potential to create precipitation. This shows that Marmara Region receives a substantial amount of precipitation from northerly and easterly maritime trajectories, implying a profound influence of the Black Sea on the rainfall regime in this area. However, rainfall at the stations that are far away or less affected by the Black Sea (especially at the ones in the west) occurs during types with a southerly component (S, SW and SE). Our results reveal that, in Marmara Region, the response of precipitation to atmospheric circulation is rather complex and spatially inhomogeneous; in line with the complex topography of the area. Therefore, water management policies should be adopted accordingly, taking all local characteristics into account.