Assessment of tornado damage utilizing Sentinel-2 imagery and orthophoto maps: case studies in the Balearic Islands

Strong convective winds and high-impact events cause significant damage to buildings, infrastructure, and forests, which we analyse using high-resolution satellite and orthophoto maps. We focused on three episodes that occurred in the Balearic Islands, located in the western Mediterranean: (i) Menorca Island on 28 October 2018, (ii) Eivissa Island on 22 October 2019, and (iii) Mallorca Island on 29 August 2020. We analyse changes in the land cover using Sentinel-2 data through the Normalized Difference Vegetation Index (NDVI). Differences in the vegetation index calculated before and after each event allow us to identify damage in forested land cover. We tested three different temporal windows: 2, 6, and 12 months. In general, we obtained the best results using images taken 6 months after each event, compared to the images taken just before the event occur. Furthermore, we conducted an analysis of the wind-thrown tree direction patterns. We compared the observed patterns in orthophoto maps with those derived from an idealized tornado-like vortex (Rankine vortex). The results confirm all three events were single tornadoes, whereas no downburst-related damage patterns could be clearly identified. We also investigated how complex orography features interact with wind-related forest disturbances. Our research showed that trees are more likely to be damaged on mountain slopes that face the wind and at the bottom of valleys that are oriented perpendicular to the storm's path. Conversely, damage gaps typically occur downwind, particularly to the leeward side of cliffs. Lastly, we estimated the dimensions of damage paths using orthophoto maps, resulting in lengths exceeding 10 km for all the cases (only 7% of reported tornadoes in Spain exceed this threshold according to previous studies) and maximum widths greater than 1 km. In fact, the Mallorca 2020 tornado's damage swath width reaches a width of 2.8 km, making it the widest ever reported in the Balearic Islands and in Spain; it is also one of the widest in Europe, according to historical records.