Abstract:

In this study, by using daily temperature observations of 77 stations, the changes and trends in the duration of the extreme temperatures during the period 1950-2017 are examined. Extreme events were defined using two temperature indices proposed by the Commission for Climatology/Climate Variability and Predictability Project’s Expert Team on Climate Change Detection, Monitoring and Indices. Selected indices are the Cold Spell Duration Index (annual count of days with at least 6 consecutive days when TN>10th percentile) and the Warm Spell Duration Index (annual count of days with at least 6 consecutive days when TX> 90th percentile). For the study period, the results of the linear trend indicated that cold spell duration tended to decrease in 67 stations, 28 of which were statistically significant. Linear trend analysis of nationally averaged time series showed that the CSDI has the decrease rate of -0.71 days per decade over the study period. The largest decreasing trend ranges were found in stations at Southeastern Anatolia and Mediterranean regions. The longest annual number of cold periods in Turkey in the first half of 1950’s, while the shortest cold periods have been observed in recent years, as was the case in 2010. Linear trend analysis of nationally averaged time series showed that Warm Spell Duration Index is mostly characterized with a generally increasing trend (+2.4 days per decade) for the entire period of 68 years. A statistically significant increasing trend for WSDI is detected at 76 stations, 45 of which are at the 0.01 significance level. In the last 68 years, the most significant increase in the annual warm spell duration is observed in the Mediterranean and the Black Sea regions. Examination of anomalies in time-series of WSDI of Turkey reveal that the annual warm spell duration was characterized with a strong positive trend after 1993, and particularly during the years of 2010, 2012 and 2016 which anomalies exceeded +3σ at many stations of Turkey. It would be worth noting that the summer of 2010 was the longest one in Turkey that exhibited the highest positive anomalies (+7.8σ) in the annual warm spell duration over the whole study period beginning from 1950 to 2017. 

Keywords: