Member spotlight: Katherine Ratliff, Duke University Nicholas School of the Environment
I am a Ph.D. candidate in the Division of Earth & Ocean Sciences at the Duke University Nicholas School of the Environment. My research focuses on landscape dynamics and the complex feedbacks within coupled human-landscape systems at the land-water interface. I seek to better understand landscape dynamics in these settings, and principally how humans have either directly modified or influenced the morphodynamics of these landscapes. I use innovative numerical models to study the larger-scale emergent interactions, allowing us to clarify the most important feedbacks and critical variables within these systems.
In my recent research with my adviser Dr. Brad Murray, I have been developing the River Avulsion and Floodplain Evolution Model (RAFEM), which I have coupled with the Coastline Evolution Model (CEM), using the Community Surface Dynamics Modeling System Basic Model Interface. With this new morphodynamic river delta model, I will explore how both upstream (e.g., changing river properties) and downstream (e.g., sea-level rise, changing wave climate) controls affect large-scale delta morphology and river avulsions. I also plan to investigate how human influences on rivers (e.g., damming and levees) and coastlines affect the dynamics and feedbacks within the system.
In previous work with Dr. Marco Marani and fellow Duke Ph.D. student Anna Braswell, I have investigated how climate change impacts
coastal marsh resilience. Coastal marshes provide numerous ecosystem services, are an important carbon sink, and are exposed to drowning as sea-level rise accelerates. Using a meta-analysis of the available observa- tional data, we model the coupled marsh vegetation and morphological dynamics. We found that the fertilization effect of elevated atmospheric CO2 significantly increases marsh resilience to drowning and decreases the spatial extent of marsh retreat under high rates of sea-level rise. While this direct CO2 fertilization effect has so far been neglected in marsh modeling, we find it is central in determining marsh survival under the foreseeable range of climatic changes (Ratliff et al, 2015 – PNAS).
Other previous work includes using modeling to better understand sediment transport dynamics within pocket beaches (Ratliff and Murray, 2014 – GRL). Previous work suggested seasonality or oscillations in climate indices control erosion and accretion along these shorelines; however, using the Coastline Evolution Model (CEM), I found that patterns of shoreline change emerge without systematic shifts in wave forcings. Using Principal Component Analysis, I identified two main modes of sediment transport dynamics: a previously studied shoreline rotation mode, and a newly discovered shoreline “breathing” mode. The characteristic timescales of these modes scale diffusively. I retroactively identified the breathing mode in observations of pocket beach shoreline change from different parts of the world. Characterization of these modes, as well as their timescales, better informs risk assessment and coastal management decisions along thinning shorelines, especially as climate change affects storminess and wave energy variations across the world.