Merging tidal datums and Lidar elevation for species distribution modeling in South San Francisco Bay

Because high tides increase in elevation across South San Francisco Bay, and because tidal inundation structures tidal salt marshes plant zonation, species distribution models (SDMs) of salt marsh plants require integrated, spatially continuous measures of tidal patterns and elevation. Continuous Lidar elevation data is available for South San Francisco Bay, but tidal datum values from National Ocean Service (NOS) tidal stations in the region are available only as point locations. In order to effectively normalize Lidar elevations to tidal heights, an interpolated data layer of tidal datums was created in ArcGIS. MHHW from 16 tide stations were extracted from tidesandcurrents.noaa.gov, translated to NAVD88 using a conversion table created by NOS for a 2005 hydrographic survey, then interpolated using the spline tool in ArcGIS. Then, the lidar elevation layer was subtracted from the MHHW layer, normalizing elevation relative to MHHW and creating an input meaningful for region wide marsh vegetation distribution models. Results and sources of error in the output are discussed.