The increasing frequency and intensity of droughts in the Mediterranean Basin poses the ecosystems of this biodiversity hotspot at risk, despite their adaptation to arid and semi-arid conditions. The concept of ecosystem resilience has been widely applied in framing the impacts of global changes on ecosystems, yet the transferability of the metrics used is rarely assessed. Moreover, estimating resilience to drought poses an additional challenge, being a multi-scalar hazard difficult to uniquely identify temporally. 

In this study, we aim to identify metrics suited to assess the impacts of drought on ecosystems in the Mediterranean Basin biome. We analyzed time series from 2001 to 2018 of drought and vegetation spectral indices across six sites, spread around the whole Basin and with different aridity and vegetation types. We used the Standardized Evapotranspiration-Precipitation Index (SPEI) at different aggregation time scales (3, 6, and 12 months), and four spectral indices — NDVI, EVI, NIRv and kNDVI — as proxies of vegetation functioning. 

We estimated the correlation between drought and vegetation indices to select the most relevant time scale for detecting droughts and their effect. Our findings show that aggregating SPEI over 12 months and using kNDVI for vegetation gives the most robust combination for detecting drought impacts. Eight vegetation response metrics were defined to represent various components of resilience. We analyzed them using an event-based approach, with droughts identified using four different SPEI thresholds. The distributions of response metrics were then compared with those from randomly occurring synthetic events to evaluate their reliability in capturing drought impact. Productivity loss and recovery emerged as the most consistent across sites and drought definition, supporting their relevance for large-scale assessments of drought resilience in Mediterranean ecosystems.