Impacts of different drought regimes on ecosystem resilience components in the Mediterranean Basin

Climate models project increasing frequency and intensity of droughts in the Mediterranean Basin, escalating the threat to ecosystems. The lack of water may result in plant wilting and cavitation, reduced resistance to disease and pests, and stronger competition between species, among many other ecological processes that might be affected. Water-limited ecosystems, like those in the Mediterranean Basin, although adapted to water scarcity, may be particularly vulnerable to extreme droughts. Understanding such dynamics across different ecosystems of the region is crucial, as it is both a biodiversity and climate change hotspot.

We examined the impact of drought regimes on the resilience of Mediterranean ecosystems, expecting to detect a nonlinear relationship between drought regimes and resilience components as successive drought events cumulate in stronger impacts on ecosystems. We employed an event-based approach to drought regime analysis, in which we measured duration, intensity, severity, and time since the last event as drought attributes. We analyzed the resilience of vegetation to droughts by extracting the temporal components of resistance and recovery. Droughts are detected using the Standardized Precipitation-Evapotranspiration Index (SPEI-12), estimated from CHELSA database products, and vegetation response is evaluated using the kernel Normalized Difference Vegetation Index (kNDVI) from the MODIS multispectral sensor as a proxy for vegetation productivity and functioning. We examined the 2001–2018 time series for several ecoregions in the Mediterranean Basin to detect the functional shape of the vegetation response curve for this region.

Our preliminary results suggest that resilience components and drought regimes characterize different aspects of ecosystem response to water stress. Arid areas featuring shrubland ecosystem types emerged as the most resilient under varying drought severity, and the resistance component across different ecosystem types presented a stronger relationship with drought duration than with intensity. Furthermore, the distribution of resilience components as a function of drought regimes exhibits multimodal patterns, thereby supporting the hypothesis of a nonlinear relationship. This suggests that the drought response modeling approach used is challenging but promising.