Characterizing anomalous climatic events (SPEI base)
To identify climatic anomalies, we chose the standardized
precipitation-evapotranspiration index (SPEI, Vicente-Serrano et
al. 2010). We compiled it for local monthly values at time scales
ranging from 1 to 48 months and at the spatial resolution 5° x 5°. This
means that, for a given month, it represents the cumulative water
balance over the previous n months. Here, we used n = 3 months
(SPEI-03), which presented the highest correlation with NDVI data. Based
on the index values, we identified for each plot, from year 2000 to
2018, dry and wet events outside the normal range (-0.68 <
SPEI < 0.68), as well as their intensity: extreme (SPEI
> |1.27|) or moderate
(|0.68| < SPEI <
|1.27|) (Vicente-Serrano et al. 2010).