A climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site: Steppingstone to climate proofing the East Asian-Australasian Flyway

5m Digital Elevation Model for Hong Kong to calculate percent slope using the function in ESRI ArcMap 10.7. These three layers (i.e., land cover, DEM, and slope) were used as the main input files for the simulations. Since there was no information on dikes this option was not applied, along with the soil saturation parameter. We also used the following input parameters: offshore direction is west; MTL-NAVD88 (m) = 0 and 0.7m, for low and high tide, respec- tively; GT Great Diurnal Tide Range (m) = 1.46 m, based on information from the Hong Kong Observatory data (https://www.hko.gov.hk/en/tide/predtide.htm?s=TBT). In this analysis, low and high tides are used to denominate different modelling scenarios. Since the average tidal range for the site is 1.46 m, we applied two scenarios of simulation; low and high tide. For the low tide scenario, we simulated no height difference between elevation data and local datum. For the high tide scenario, we applied 0.7 m of height difference, which represents half of the total tidal range. The objective was to derive two results to define a range (i.e. minimum and maximum), since the exact delineation of the shoreline is unknown. The choice for 0.7 m was made after a sensitivity analysis over the “time-zero” run of SLAMM to calibrate the model to site-specific data. We then tested the model with increasing heights until we perceived changes in the classes and selected 0.7 m as the upper boundary, therefore called high-tide scenario. Results There was no discernible impact to the habitats in Mai Po until after 2075, and we do not pres-

ent the results for the earlier timelines here. However, projections for 2100 suggest that overall, the mangroves, marshes and tidal flats are impacted in almost all scenarios of SLR and accre- tion (Table 2). Under a 1.5 m SLR scenario, at low tide there was little change in the tidal mud- flats and coastal mangroves if the current accretion levels of 8 mm/yr or more continues into the future (Table 2, Fig 2). However, if accretion levels decrease, as predicted, to 4 mm/yr, the tidal flats are expected to be inundated even during low tide with over 77% being lost as habitat for wading and shorebirds, while the mangroves remain relatively unaffected (Table 2, Fig 2). When accretion levels decline to 2 mm/yr, over half the coastal mangroves could also be lost due to permanent inundation of the coastal areas, including during low tide (Table 2, Fig 2). A Table 1. Land use and habitat categories in Mai Po Inner Deep Bay Ramsar site and Wetland Conservation Area cross-walked to SLAMM categories (based on SLAMM 6.7 technical documentation, Clough et al. [26]). Land use and habitat classes in Mai Po SLAMM categories SLAMM Code Urban; Buildings; Built up areas Developed Dry Land 1 Bare soil; Pond bunds; Gei wai/pond islands in nature reserve; Mixed vegetation; Sparse tree/forest Undeveloped Dry Land 2 Marshes (inland and outside the Ramsar site); Reedbeds outside nature reserve and pond 23/24 in nature reserve Inland-Fresh Marsh 5 Reedbed and emergent in nature reserve ponds Regularly-Flooded Marsh 8 Mangrove Mangrove 9

Intertidal mudflats; Beach, Tidal Marsh (along Kam Tin River) Tidal Flat 11 Freshwater ponds in nature reserve; Lily ponds in nature reserve; Fishponds inside Wetland Conservation Area Inland Open Water 15 Tidal channel (through tidal flat), River Riverine Tidal 16 Ponds adjacent to the Shenzhen River; Open water areas in nature reserve ponds Estuarine Open Water 17 Open water and riparian vegetation along tidal Creeks Tidal Creek 18 https://doi.org/10.1371/journal.pone.0239945.t001 PLOS ONE Climate adaptation strategy for Mai Po Inner Deep Bay Ramsar site PLOS ONE | https://doi.org/10.1371/journal.pone.0239945 October 21, 2020 6 / 16