Assessing variations in climate extremes over Euphrates Basin, Turkey

The variation in climate extremes at different spatial and temporal scales can be conceived as an important indicator of climate change. The focus of this study is to reveal linear trends and observe space-time (ST) variation in extreme climate indices over the Euphrates Basin in Turkey. Extreme climate indices are calculated using daily maximum, minimum, and mean temperatures, including observations of daily precipitation measured from 41 meteorological stations from 1970 to 2017. Three precipitation indices, consecutive dry days (CDD), consecutive wet days (CWD), and precipitation intensity (SDII), together with three temperature indices, number of summer days (SU), number of frost days (FD), and growing season length (GSL), are analysed. Linear trends in these extreme indices are examined using the Mann-Kendall test. The ST distribution and variation in climate indices are examined through prediction maps for this study period. Ordinary kriging (OK), which has proven to be accurate and reliable in many studies, is used to obtain prediction maps on ST framework. Results indicated that there is an evident trend in the temperature-related indices. Regarding SU and GSL, about 66% and 34% of all stations, respectively, show a significant increasing trend. The downward trend (negative Z statistic) for the FD is observed at approximately 83% of all meteorological stations, of which 35% show a significant trend. The ST variation in temperature-related extremes is evident from prediction maps; the trend is not as dominant for precipitation-related indices. In terms of ST prediction maps, the most prominent variation is observed in the south and northeast parts of the basin in CDD and CWD prediction maps from 2013 to 2017.