Environmental Impacts of Sea Level Rise in the Galveston Bay, Texas Region

Anthropogenic effects throughout the twenty-first century, particularly greenhouse gas emissions, have contributed to global climatic and environmental changes. Sea level rise (SLR) is one of these changes occurring along the Texas coast and is amplified by local land surface subsidence due to oil and gas extraction, groundwater withdrawal, and compaction of Holocene sediments. SLR along the northern Texas coast is impacting critical coastal wetland environments, which are especially vulnerable due to their low-lying nature and the presence of extensive development impeding upland migration. Sea level data from the NOAA tide gauge at Galveston Pier 21 has shown an increase of 0.6 meters in relative sea level in the past 100 years. Given an expected increase in the rate of SLR in the next decades, the purpose of this study is to provide an in-depth assessment of the effects of relative SLR on the habitat distribution of coastal wetlands in the Galveston Bay region. In this study, three SLR scenarios are modeled: (1) a scenario based on a linear extrapolation of satellite altimetry data (0.21 m by 2100); (2) the IPCC’s RCP8.5 mean scenario (0.74 m by 2100); and (3) a high-end scenario (1.8 m by 2100) based on the 95th percentiles in the uncertainty distributions of estimates of individual SLR components simulated for the RCP8.5 scenario. A land subsidence rate calculated by developing a subsidence grid using GPS-measured subsidence monitoring and releveling data is added to all three scenarios. The Sea Level Affecting Marshes Model (SLAMM) is used to predict wetland conversion due to long-term SLR incorporating the processes of inundation, erosion, accretion, and saturation. Results indicate that both salt marshes and fresh marshes face a significant risk of submergence due to even small increases in sea level. Although salt marsh is predicted to increase in the low scenario by 2100 (15,851 ha gained, 37% increase from 2007), the high scenario shows large losses (4,772 ha lost, 11% of 2007 area). Potential losses of fresh marshes are significant in both the low scenario by 2100 (15,298 ha, 18% decrease from 2007) and the high scenario (37,816 ha lost, 44% decrease from 2007). This research effort to assess the physical and environmental impacts due to SLR is intended to enable policy-makers, managers, and the general public to evaluate the impacts or risks of private and public land use decisions in the Galveston Bay region.