Modelling the response of mangroves and saltmarshes to sea-level rise: model development and validation

Abstract

Models of the response of mangrove forests and saltmarshes to sea-level rise are needed to inform coastal decision making. Zero-dimensional models that simulate evolution of a point are foundational for developing spatially explicit landscape models projecting coastal wetland extents under future sea-level rise scenarios. However, both zero-dimensional and spatially explicit landscape models have suffered from insufficient calibration and inadequate validation. In this study, a zero-dimensional model framework was parameterised using real data from four sub-sites exhibiting varying rates of mineral and organic matter addition and autocompaction. The model was calibrated to correspond to tidal parameters at each sub-site and validation was undertaken across three timescales to assess model efficacy. Short-term validation encompassed the period over which measurements of surface elevation gain were determined using a network of surface elevation tables (~20 years); medium-term validation encompassed the period when higher resolution colour aerial photography was available (~35 years); and long-term validation focussed on the period of landscape evolution occurring since the mid-Holocene. The model performed well at the medium to long-term scale and was within the range of variability arising from surface elevation table measurements. This study demonstrates the critical need for site-specific data, a crucial component that is undervalued, often insufficiently resourced to generate useful data, and commonly addressed by extrapolating parameters generated from elsewhere. Validation has provided the necessary confidence for further model development at the landscape scale that will account for processes operating both vertically and laterally, such as shoreline erosion and tidal creek extension.