On September 20, 2017, Hurricane Maria hit the U.S. territory of Puerto Rico as a category 4 storm. Heavy rainfall caused landslides in mountainous regions throughout the territory. This data release presents geospatial data describing the concentration of landslides generated by Hurricane Maria in Puerto Rico. We used post-hurricane satellite and aerial imagery collected between September 26, 2017 and October 8, 2017 to visually estimate the number of landslides over nearly the whole territory. This was done by dividing the territory into a grid with 4 km2 cells (2 km x 2 km). Each 4 km2 grid cell was classified as either containing no landslides, fewer than 25 landslides/km2 or more than 25 landslides/km2. We used 12 WorldView satellite images (~0.5 m-resolution) available from Digital Globe, Inc. and ~0.15 m-resolution aerial imagery collected by Sanborn and QuantumSpatial (http://www.arcgis.com/home/item.html?id=b1949283c1084b0daf2987d896392ac2). Because leaves were stripped from much of the vegetation, landslide scars were readily visible in both sources of imagery. We assume that the majority of landslides were triggered by rainfall from Hurricane Maria, but rainfall from Hurricane Irma during the first week of September and rainfall from thunderstorms after Hurricane Maria may have also initiated landslides.
During this investigation, we visually examined a total area of 8103 km2, which encompassed most of the territory and nearly all the mountainous areas. Approximately 846 km2 of the land area of the territory was not examined because either 1) imagery was unavailable or 2) the area was obscured by cloud cover. Approximately 61% of the examined area was unaffected by landslides. Landslides were observed in the remaining 39% of the examined area, but, for the most part , the landslide density was less than 25 landslides/km2 (37% of the examined area). Landslide density was greater than 25 landslides/km2 in about 2% of the examined area (156 km2), which includes parts of the Añasco, Mayagüez, Las Marías, Maricao, Lares, Utuado, Adjuntas, and Jayuya municipalities. Based on visual examination of imagery, the municipality of Utuado appears to have been the most severely impacted, with about 40% of the municipality having a density of landslides greater than 25 landslides/km2. This preliminary assessment serves to inform response and recovery efforts and as a basis for more detailed studies on the impacts of landslides in Puerto Rico caused by Hurricane Maria.