A marsh multimodel approach to inform future marsh management under accelerating sea-level rise

Accelerating sea-level rise combined with the stresses of human land use threatens the persistence of tidal marshes. The proper management of existing marshes and the conservation of lands for marsh migration require a synthesis of factors affecting future marsh evolution.There are a number of existing marsh models, with different parameters and run at different scales, that can assist in this type of assessment. However, as with many models forecasting future conditions, there is no clearly identified 'best' model and they all perform slightly differently across different scenarios and with different suites of available data inputs.In this paper, we worked with local and regional managers to inform the development of an ensemble methodology that uses results from multiple marsh models in conjunction with social, land use and environmental data to inform marsh management, conservation and restoration under sea-level rise.The methodology was developed and tested in three locations in the Virginia portion of the Chesapeake Bay, United States, using existing marsh migration models already run throughout the Bay. Stakeholder groups of local decision makers and a steering committee composed of regional managers were engaged in the process to ensure that the resulting methodology met current management needs.The need for a multimodel approach to identifying marsh migration pathways was supported by the marsh migration comparison done during methodology development which showed disparate results from multiple marsh migration models. Five existing marsh model outputs were combined into a single Marsh Migration Corridor Envelope (MMCE), which encompasses the potential area of current upland expected to become marsh under a selected sea-level rise scenario.Within the identified MMCE, land covers were assessed for suitability for marsh support and the socio-economic context of the parcels of land was considered. Last, the current condition of existing marsh on the properties was assessed to determine preservation activities that can increase their longevity. Together, these pieces of information inform a physical and sociological understanding of tidal marshes that can allow for a management framework that incorporates both current and future concerns. As marshes migrate under the influence of sea-level rise, they move into upland areas. Conserving those areas can be critical to ensure that marshes persist into the future. Decision makers need actionable information on which areas are most likely to benefit from conservation.image