Investigation of changes in corn yield with agricultural drought indices in some provinces of Aegean region

A comparative performance analysis was studied on well known drought indices (Standardized Precipitation Index (SPI), Palmer Drought Severity Index (PDSI) and its moisture anomaly index (Orig-Z), self-calibrated Palmer Drought Severity Index (SC-PDSI) and its moisture anomaly index (SC-Z)) to determine the most appropriate index for assessing corn (Zea mays L.) yield in four crop regions (Aydın, Denizli, Afyonkarahisar, Uşak) in western Turkey for the period of 1963 to 2007. There are two steps for developing corn yield models. First, a series of curvilinear regression based crop-yield models were developed for each of the crop region based on the drought indices. Each regression model was formulated using a second-order polynomial fit to the data, where the independent variable was a growing season drought index. Second, each corn yield model was tested to find a best appropriate model for the crop regions. In Aydın crop region, the SC-PDSI index was the best performed model of the five drought indices. This index was correlated with the corn yield departures with a R2 value of 0.4251. In Denizli, Afyonkarahisar and Uşak crop regions, the PDSI was the best efficient model. This index explained 41%, 43%, and 42% of the variability in the observed data of Denizli, Afyonkarahisar and Uşak regions, respectively. In the Aegean region, drought indices based corn yield models can explain approximately 40% of changes in corn yield. Rest of the variability in corn yield, approximately 60%, is influenced by other parameters but climate parameters.Key words: drought indices, crop-yield models, Aegean Region