3.1.3. Storm Classification

Once all of the storm events are identified, ST-CORA classifies storm events into two types: small convective systems with a short duration (short-lived) and long duration systems extended over large areas (long-lived) [64,65]. We used an unsupervised K-means cluster analysis method to classify shortand long-lived storm events based on the four main storm characteristics (duration, spatial extent, maximum intensity, and total volume). This method divides *n* observations into *k* clusters in which each observation is a member of the cluster that minimises the objective function *J*, as follows:

$$J = \sum\_{j=1}^{k} \sum\_{i=1}^{n} \|X\_{(x,y,z,c)}\|\_{i}^{j} - C\_{j} \|\|^{2} \tag{5}$$

where, *X* is the storm with dimensions *x*, *y*, *z*, *c* corresponding to the storm characteristics duration, spatial extent, maximum intensity and total volume, respectively. *C* is the centroid of the cluster *k* and the absolute number represents the minimum Euclidean distance to *C*.
