Impact of climate change on floodplain inundation and hydrological connectivity between wetlands and rivers in a tropical river catchment

Surface water connectivity between waterbodies in a river-floodplain system is considered one of the key determinants of habitat quality, biodiversity and ecological integrity. This manuscript presents results from an investigation into the potential changes in floodplain inundation and connectivity between wetlands and rivers under projected future climates, in a large river catchment in Western Australia. The study was conducted using a two-dimensional hydrodynamic model (MIKE 21), and the modelling domain included the floodplain reaches encompassing the ecologically important wetlands. A lumped rainfall-runoff model (SIMHYD) was used to estimate local runoff and inflows from ungauged catchments. A SRTM derived 30-m elevation data was used to parameterize land topography and stream networks in the hydrodynamic model. Hydraulic roughness parameters were estimated using a land cover map, which was developed using a combination of aerial photography, topographic maps and Google Earth imagery. The hydrodynamic model was calibrated using stream gauge data and flood inundation maps derived from Moderate Resolution Imaging Spectroradiometer imagery. Model simulated stage heights were combined with land topography to identify floodplain pathways that connect wetlands with rivers. The connectivity of 30 off-stream wetlands was evaluated under present and future climates. The duration of connection of the individual wetlands to the main river channel varied from 1 to 40days depending on flood magnitude and duration. Topographic relief, location on the floodplain and magnitude and duration of the flood were found to be key factors governing the level of connectivity, and the relationship between return period of flood and inundated area was found to be non-linear. Modelling under a drier future climate indicated that the duration of connectivity of wetlands could be up to 20% less than under the current climate, whilst under a wetter climate the connectivity could be 5% longer. The results of this study provide potential use for future studies on movement and recruitment patterns of aquatic biota, wetland habitat characteristics and water quality and wetland biodiversity assessment.