Seasonal ecosystem vulnerability to climatic anomalies in the Mediterranean

The ecosystems of the Mediterranean Basin are particularly prone to climate change and related alterations in climatic anomalies. The seasonal timing of climatic anomalies is crucial for the assessment of the corresponding ecosystem impacts; however, the incorporation of seasonality is neglected in many studies. We quantify ecosystem vulnerability by investigating deviations of the climatic drivers temperature and soil moisture during phases of low ecosystem productivity for each month of the year over the period 1999 – 2019. The fraction of absorbed photosynthetically active radiation (FAPAR) is used as a proxy for ecosystem productivity. Air temperature is obtained from the reanalysis data set ERA5 Land and soil moisture and FAPAR satellite products are retrieved from ESA CCI and Copernicus Global Land Service, respectively. Our results show that Mediterranean ecosystems are vulnerable to three soil moisture regimes during the course of the year. A phase of vulnerability to hot and dry conditions during late spring to midsummer is followed by a period of vulnerability to cold and dry conditions in autumn. The third phase is characterized by cold and wet conditions coinciding with low ecosystem productivity in winter and early spring. These phases illustrate well the shift between a soil moisture-limited regime in summer and an energy-limited regime in winter in the Mediterranean Basin. Notably, the vulnerability to hot and dry conditions during the course of the year is prolonged by several months in the Eastern Mediterranean compared to the Western Mediterranean. Our approach facilitates a better understanding of ecosystem vulnerability at certain stages during the year and is easily transferable to other study areas and ecoclimatological variables.