Trend direction changes of Turkish temperature series in the first half of 1990s

Abstract

The presented study was concentrated on the trend analysis of the annual mean temperature series of 40 meteorological stations in all climatic zones of Turkey. The sensitivity of the parametric and nonparametric tests to the selected record periods was investigated in detail. Backward-shifted and forward-shifted trend analyses were accomplished by keeping either the beginning or the ending data period constant and varying the other period ending. This analysis resulted with a trend statistic direction turning point at the year 1992. Following this result, the trend tests were applied to three different records to distinguish the effect of 1992 on the trend direction. For the period 1950-1992, the downward trend was dominating several stations whereas only upward trend was observed for 1986-2006 period. Clearly, the trend direction change in 1992 dominated the trend behavior between 1986 and 2006. The opposite trend orientations on 1950-1992 and 1986-2006 periods seem to be neutralized on 1950-2006 period with the majority of the stations showing no trend as the result. This study displays the effect of different lengths of data record on the trend analysis results. It has been clear by this study that a sudden change on trend direction is obvious at the stations above 39 degrees N in Turkey provinces in 1992. These results are conformed to the previous studies related with climate change like temperature, sea level, meteorological observations, and dominant climatic events as North Atlantic Oscillation and El-Ni (n) over tildeo and Southern Oscillation.