Analyzing Vulnerability by Integrating a Landslide Impact Assessment and Social Vulnerability Index Analysis: A Case Study of the Río Grande de Añasco Watershed Post Hurricane Maria

Abstract. Hurricane Maria triggered more than 16,000 landslides across the Río Grande de Añasco Watershed, contributing to system-wide failures of critical road infrastructure, stormwater drainage, and damage to homes and farms (Figure 1). Assessing the spatial relationship between the distribution and density of the landslides relative to transportation networks and primary stream input points identifies critical areas for prioritizing recovery and mitigation efforts across this diverse and complex socio-ecological landscape within the Añasco Watershed. Furthermore, considering social context alongside physical and natural science principles contributes to applied scientific inquiry addressing the complex challenges facing a Small Island Developing State (SIDS) in this climate-vulnerable region. Within the socio-ecological landscape, issues surround extremes of wealth and poverty, disenfranchised populations, and disconnected systems, to name a few. This study examines the intersection of the CDC Socio-economic Vulnerability Index with a landslide impact assessment to better understand how social system exposures and vulnerabilities intersect with landscape vulnerabilities and risk. A geospatial proximity analysis comparing the density and area of slides with river networks and manufactured drainage systems highlights future sources of significant sedimentation affecting issues of water quality, erosion control, and ecosystem response and resilience in the face of extreme storm events and observed changes in regional as well as local climate. For example, while the vast majority of landslides occurred within areas dominated by forest land cover, over 1,000 landslides occurred within areas designated by crops in lowland and mountain farming communities. An assessment of landslide density and incidence relative to a critical proximity to roads (325 ft or ~100m) highlights priority regions for focused examination of sustainable land use management practices and road maintenance/mitigation. Landslide distribution in regions dominated by clay soils contributes to the understanding of landscape vulnerability across the watershed. This may also prove key for national housing authority projects examining investments in reconstruction, repair, and potential relocation of communities out of high-hazard regions. Sustainable land use and effective collaborative watershed scale management will play an ongoing role in mitigating repeat failures of slopes and reducing overall sedimentation throughout the watershed. This socio-ecological system evaluation aids a watershed scale risk assessment by exploring opportunities for a multi-system approach to empowering community involvement in sustainable, long-term governance and improved land use and erosion mitigation practices.