Misconception of coastal resilience caused by inconsistent resolution in bathymetry mapping

Long-term time series of bathymetric data of coastal zones are indispensable for analysing coastal morphological resilience to climate change. Despite the increasing popularity of utilizing high-resolution gridded bathymetric digital elevation models for coastal management, potential errors in analysing the long-term trend of mean elevation change from historical bathymetric datasets spanning a period of multiple years to decades have attracted little attention. Here, we demonstrate that inconsistency in the spatial resolution of small-scale topographic features characterized by sharp bathymetric gradients, such as tidal creeks and streams, could produce an artificial false trend of mean elevation change that is on the same or even higher order of the sea level change rate. Neglecting this inconsistency may lead to a misconception of coastal resilience to sea level rise and misguide planning and implementation of coastal protection strategies. We provide an analytical method to identify such inconsistency in time series of gridded digital elevation models and a homogenization method to minimise the associated errors. Our methods are broadly applicable to reduce errors in bathymetric analysis and improve quantitative assessment of coastal resilience to climate change.