Assessment of future olive crop yield by a comparative evaluation of drought indices: a case study in western Turkey

A comparative performance analysis was studied on well-known drought indices (Standardized Precipitation Index, Palmer Drought Severity Index (PDSI) and its moisture anomaly index (Orig-Z), and self-calibrated Palmer Drought Severity Index (SC-PDSI) and its moisture anomaly index (SC-Z)) to determine the most appropriate index for assessing olive ( O. europaea L.) yield for oil in seven crop regions (Muğla, Aydın, İzmir, Manisa, Balıkesir, Çanakkale, and Bursa) in western Turkey and to evaluate the vulnerability of olive yield for oil to climate change with future projections provided by the Hadley Centre for Climate Prediction and Research ENSEMBLES project (HadCM3Q0). A series of curvilinear regression-based crop yield models were developed for each of the olive-growing regions based on the drought indices. The crop yield model that performed the best was the SC-PDSI model in Muğla, Aydın, İzmir, and Manisa regions and the PDSI model in Çanakkale, Balıkesir, and Bursa regions. The SC-PDSI index-based model described 65%, 62%, 61%, and 62% of the measured variability of olive yield in Muğla, Aydın, İzmir, and Manisa regions, respectively. The PDSI index-based model explained 59%, 58%, and 64% of the measured variability of olive yield in Balıkesir, Çanakkale, and Bursa regions, respectively. The vulnerability of the olive yield for oil to HadCM3Q0 future climate projections was evaluated for Aydın and Çanakkale regions due to the resolution of the regional climate model. In terms of the future scenarios, the expected decrease in olive yield residuals was 2.5 ton (10 3 trees) −1 and 1.78 ton (10 3 trees) −1 in Aydın and Çanakkale regions, respectively.