Changes in the climatic growing season in western Anatolia, Turkey

In this study spatial and temporal variations of climatic growing season parameters in western Anatolia, Turkey, during 1966-2015 are analysed. The beginning of the growing season (end of the growing season) for all threshold values of 5, 7 and 10 degrees C is delayed (advances) from the southwest to the northeast over the study area. The growing season length (GSL) increases from northeast to southwest. The growing season start (GSS), growing season end (GSE) and GSL are strongly correlated with elevation, low-elevation stations having earlier GSS, later GSE and longer GSL than stations at higher elevations. The regional average GSS shifted 7.3, 10.0 and 10.5 days earlier, while the regional average GSE moved 4.8, 6.1 and 6.2 days later, increasing the GSL by 12.0, 16.6 and 15.9 days for 5, 7 and 10 degrees C, respectively. A comparison of mean values between subperiods documented significant changes at more than 50% of stations for GSS and GSL from the subperiod 1977-1997 to the subperiod 1998-2015 and almost no significant change between 1966-1976 and 1977-1997 for all thresholds. Correlation analysis showed that the East Atlantic Pattern was the main driver for GSS and the North Sea-Caspian Pattern for GSE, followed by the East Atlantic/Western Russia Pattern and the North Atlantic Oscillation, respectively. Monthly and annual precipitation totals and precipitation distribution within a year have not changed significantly, suggesting that air temperature has become more influential on GSS and GSE.