Inconsistency of resolution in bathymetry mapping may lead to misconception of coastal resilience to climate change

As science and technology continue to advance, the accuracy of coastal and ocean bathymetry mapping continues to improve. Bathymetric mapping of coastal zones usually integrates products from multiple instruments for optical sensing (satellite, LiDAR) and/or acoustic sensing (single beam, multibeam and sidescan sonars) that are of varying accuracy and spatial resolution. Merging of these data from different sources may lead to spatial and temporal inconsistencies in the joint bathymetric data and inhibits their use for reliable assessment of coastal resilience to climate change such as sea level rise. This particularly requires caution since the rate of sea level change is typically on the order of a few mm yr^-1, which is much smaller than the accuracy of bathymetric data, e.g. the accuracy ranges from the order of a few cm for LiDAR and multibeam eco sounding data to a few tens of cm for satellite data. In this study, we first demonstrate a problem, which is often overlooked in existing literature, in using coastal bathymetric data derived from state-of-the-art techniques for assessing coastal resilience to sea level rise. Using the Germen Wadden Sea as example, we found that the inconsistency of spatial resolution in the bathymetry mapping, when merged into a uniform gridded dataset, could result in a false trend in the change of the mean elevation of tidal basins, leading to a misconception of coastal resilience to sea level rise. We developed an analytical method to identify inconsistency in gridded bathymetry dataset that can be applied worldwide. Based on the identified inconsistency, we propose two solutions to minimise the associated effect. Our methods are broadly applicable to reduce the error in coastal bathymetry mapping and improve quantitative assessment of coastal resilience to climate change.