TREND OF STANDARDIZED PRECIPITATION AND EVAPOTRANSPIRATION INDEX (SPEI) OVER TURKEY
R. Jamal1, S.J. Hadi2, M. Tombul1
1Eskisehir Technical University, Eskisehir, Turkey
2University of Tikrit, Tikrit, Iraq
Keywords: droughts, climate change, trend slope coefficient, monthly mean air temperature, amount of precipitation
Abstract
The paper examines drought trends in Turkey due to climate change. Therefore, forecasting periods of drought, which is one of the major negative side effects of climate change, is essential. The authors used data from drought indicators according to the SPEI (Standardized Precipitation and Evotranspiration Index) for the period between 1901 and 2015. Values obtained at intervals of 1, 3, 6 and 12 months. The data was subjected to several statistical tests: the Mann-Kendall test to determine the direction and significance of the trend, the Theil-Sen estimator to assess the trend slope coefficient, and the Pettitt-test to determine the most probable year of change. The period under study was divided into two intervals (1901-1981 and 1982-2015), and their comparison was performed. A GIS program was used to isolate spatial characteristics from the results obtained. It was concluded that Turkey is mainly divided into two zones of drought, most of which is an increase in moisture in the northern regions, while a decrease in moisture is observed in the southern regions. The trend towards dry periods was more significant until 1981, but since 1981 the situation has changed due to the onset of the trend towards excess moisture, with the exception of southeastern Turkey, where the trend towards droughts persisted.
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