Spatiotemporal Measures of Exposure and Sensitivity to Climatic Variability and Change: The Cases of Modern Sea Level Rise and Southwestern U.S. Bioclimate

Abstract

Human activities are the main driver of environmental changes over the past 100-200 years, and threaten the stability of Earth's environmental systems. One part of Earth's environment already destabilized due to human activities is its climate. With human-caused changes to Earth's climate expected to continue, questions arise as to which, where, and when impacts to human and natural systems might occur. Understanding the vulnerability - the exposure, sensitivity, and resilience - of a system to changes in climate is essential to addressing these questions. This study represents an assessment of system vulnerability to climate change through the cases of modern sea level rise (SLR) and southwestern U.S. (SW) bioclimate. SLR is an important consequence of human-caused climate change, as higher seas have the potential to cause major social, environmental, and economic impacts. With a focus on sensitivity to SLR, we developed a new geospatial dataset that delineates low-lying coastal areas and overlaid this dataset with boundaries of U.S. cities with populations greater than 50,000 to determine areas prone to SLR impacts in this and subsequent centuries. Results demonstrate that potential SLR impacts to 180 U.S. cities will be very local and disproportionate. Recent warm and dry conditions have altered SW bioclimate, and expected further increases in regional temperatures raise concern that anomalous growing conditions will continue to occur and, in cases, worsen in the future. With a focus on exposure of SW vegetation to changing growing conditions, we compared the 1950s and 2000s droughts to take advantage of the opportunity to study mesoscale ecosystem responses to anomalously dry conditions before and during the regional warming. Higher temperatures and evapotranspirational demand during the more recent drought altered the degree to which climate limited foliar growth. These climatic conditions reduced effects of suboptimal temperatures on foliar growth at lower elevations in winter and higher elevations in summer. They also increased constraints of evapotranspirational demand on foliar growth at lower and middle elevations from spring through summer. Free-tropospheric air temperatures, a strong influence on climate in mountainous areas, support statistical downscaling of projected SW temperatures to assess if and when similar or more anomalous conditions will occur in upcoming decades. Assessing the vulnerability of a system to changes in Earth's climate like those taking place and projected to happen is a way for environmental sciences to help inform policy decisions that consequently stem from past or potential impacts of climatic hazards.