Temporal Change of Climatological Precipitation Deficit Index in the Buyuk Menderes Basin, Turkey

###EgeUn###Climatological precipitation deficit index (PD) is one the indices used to monitor agricultural drought by examining the difference between precipitation and evapotranspiration. In this study, the meteorological stations located in the Buyuk Menderes Basin, which has an important agricultural potential for Turkey, are used to determine the PD and its temporal variation by Mann-Kendall trend analysis using the monthly climate data of the period 1975 to 2014. The long-term average rainfall in the Buyuk Menderes Basin is 574 mm, the reference evapotranspiration is 1225 mm, and the average PD value is 651 mm. It was observed that the value of the precipitation deficit in the basin varies considerably in the long term. The trend analysis showed five of the six stations in the basin to have an increasing trend, which in three of these five stations was statistically significant. It was concluded that the increasing trend determined in the precipitation deficit derived more from the increases determined in the ET0 values than from the decrease in precipitation