Recent trends in vegetation phenology across the southern Mediterranean region, and potential climatic drivers

The agriculture sector is sensitive to changes in weather and climate, notably extreme events. Extreme variations in weather conditions throughout a growing season led to changes in phenological features of vegetation and crops and cause variations in harvest, and, generally, the impact could be large in terms of production amounts and then food security in the region. The last version of the Intergovernmental Panel on Climate Change report (IPCC) highlighted the southern Mediterranean region as a hot spot and one of the most vulnerable regions in the world. While numerous studies have addressed changes in climate extremes throughout the world, very little research has been conducted in the southern Mediterranean region concerning the seasonal concurrence of climate extremes, and their evolutions in recent decades.  Moreover, understanding the impacts of these changes on vegetation phenology is crucial in the region, but this is yet to be studied.

This study evaluates the impact of climate extremes on vegetation phenology in the southern Mediterranean region over the last 40 years. Firstly, the trends of 15 phenological vegetation indicators (e.g., length of the growing season, maximum Normalized Difference Vegetation Index [NDVI] value/time, onset/offset times, green upslope, brown downslope, etc.) are examined using National Oceanic and Atmospheric Administration [NOAA] satellite images and the modified Mann-Kendall trend test. Secondly, we examine how recent trends in vegetation phenology compare with those observed in various heat-related indices (heat wave characteristics), water-related indices (Standard Precipitation Index [SPI], Standard Precipitation Evapotranspiration Index [SPEI], Extreme Precipitation, Wet/Dry spells), and compound indices (Dry-Cold, Dry-Hot, Wet-Cold, Wet-Hot events) calculated using the ERA5-land dataset. Finally, we examine the relative importance of each climate indicator in explaining multi-year changes in vegetation phenology. As such, this study not only identifies the areas with higher risk and vulnerability for vegetation and crops in the last years but also identifies potential predictors for seamless seasonal-to-decadal forecasts of agrometeorological risks across the region.