Associations between large-scale climate oscillations and land surface phenology in Iran

Variations in land surface phenology arising from large-scale and regional climatic oscillations are important determinants for environmental and ecological conditions. Spearman's correlation coefficient was employed to delineate, within the geographical territory of Iran, the relationship between phenological metrics [cumulative NDVI (cumNDVI), start of growing season (SOS), and end of growing season (EOS)], which were obtained using the Normalized Difference Vegetation Index (NDVI) derived from the AVHRR Global Inventory Modeling and Mapping Studies (GIMMS), and six large-scale climate oscillations [the Arctic Oscillation (AO), the Dipole Mode Index (DMI), the Multivariate El Nino Southern Oscillation Index (MEI), the North Atlantic Oscillation (NAO), the North Sea-Caspian Pattern (NCP), and the Pacific Decadal Oscillation (PDO)]. Results showed that the NCP and NAO had the greatest association, while the AO and MEI had the least association, with the studied phenological metrics for the different types of vegetation in Iran. The NCP was significantly correlated with 25-41% of the pixels for the different vegetation types. The climate oscillations that dominated the relation to phenological metrics differed depending on whether relations with current or previous year climatic oscillation indices were used. The results have implications for environmental and ecological forecasting and analysis, especially for vegetation trends in Iran's arid to semi-arid climate.