Rapid remote sensing assessment of impacts from Hurricane Maria on forests of Puerto Rico
Hurricane Maria made landfall as a strong Category 4 storm in southeast Puerto Rico on September 20th, 2018. The powerful storm traversed the island in a northwesterly direction causing widespread destruction. This study focused on a rapid assessment of Hurricane Maria's impact to Puerto Rico's forests. Calibrated and corrected Landsat 8 image composites for the entire island were generated using Google Earth Engine for a comparable pre Maria and post Maria time period that accounted for phenology. Spectral mixture analysis (SMA) using image derived endmembers was carried out on both composites to calculate the change in the non photosynthetic vegetation (DNPV) spectral response, a metric that quantifies the increased fraction of exposed wood and surface litter associated with tree mortality and crown damage from the storm. Hurricane simulations were also conducted using the Weather Research and Forecasting (WRF) regional climate model to estimate wind speeds associated with forest disturbance. Dramatic changes in forest structure across the entire island were evident from preand post Maria composited Landsat 8 images. A DNPV map for only the forested pixels illustrated significant spatial variability in disturbance, with emergent patterns associated with factors such as slope, aspect and elevation. An initial order of magnitude impact estimate based on previous work indicated that Hurricane Maria may have caused mortality and severe damage to 23 31 million trees. Additional field work and image analyses are required to further detail the impact of Hurricane Maria to Puerto Rico forests. Author Comment The analyses and results from this work represent a rapid response capability following natural disasters impacting forested ecosystems. Datasets are publicly available, and a set of user interface tools is being developed for a variety of stakeholder end uses. These tools and resources will be further developed, and provided on the NGEE Tropics website https:/ngee tropics.lbl.gov/hurricane maria impacts to puerto rico/ Introduction Hurricane Maria made landfall as a strong Category 4 (Saffir Simpson hurricane wind scale) storm with maximum sustained winds of ~250 km h near Yabucoa Harbor in far southeast Puerto Rico early morning of September 20th, 2018 (Fig. 1) Maria traversed Puerto Rico in a northwest direction, exiting near the city of Arecibo, and causing widespread destruction across the island. A few weeks earlier on September 6th, Category 5 Hurricane Irma had passed within ~80 km north of the island, with sustained winds of ~300 km h and damage primarily in the northwest region of the island. This report is focused on the impacts of these powerful storms on Puerto Rico's forests, with an emphasis on the impacts of Hurricane Maria. Cyclonic storms represent a dominant natural disturbance in temperate and tropical forests in coastal regions of North and Central America (Boose et al 1994, Everham and Brokaw 1996, Mabry, et al 1998, Platt et al 2000, McNab et al 2004) Given Puerto Rico's location in the northeast Caribbean between the Caribbean Sea and Atlantic Ocean, the island is vulnerable to hurricane impacts. In the second half of the 20 century, the island was struck by two severe hurricanes and several minor storms. After a 66 year period with relatively little hurricane damage, Hurricane Hugo, a Category 4 storm, struck the island in September 1989 causing