Variation of Seasonal and Annual Rainfall Series over Southeastern Anatolian Project Area

Aims In this study, variation in annual and seasonal rainfalls in Southeastern Anatolian Project (GAP) area was analyzed using the non-parametric and parametric approaches. Materials & Methods According to the aim of the study, the data sets of the seasonal and annual timescales, based on monthly rainfalls in the GAP area, including 9 rain gauges operated by Turkish State Meteorological Service, were considered in the study. Mann–Kendall (MK) and unit root test to detect the direction of an available monotonic trend in any given data were used while obtaining the magnitude of the variation with Theil–Sen slope estimator. Findings Based on the MK test, decreasing trend in four of the seven different time scales was observed, whereas there was an upward trend in the only two (P-III and P-IV) of the all time scales while none of the stations in the P-II period showed a monotonic trend. However, the parametric unit root test detected the existence of variation in the period III for Sanliurfa station and the period V for Sirnak station. Conclusion The percentage change calculated by considering the MK varied between 19 and 57%.