Prospects and challenges of simulating river channel response to future climate change

Abstract

Due to the predicted impacts of future climate on hydrology, morphological changes to river channels are expected. Quantifying the magnitudes and rates of future channel change is important for sustainable river channel management. To date, reviews of simulation approaches for investigating river channels and the modelling of environmental change impacts on channel form and process have focused on contemporary process or palaeo perspectives. Hence, herein we review numerical modelling approaches available for reach-scale simulation of future river channels and the predicted in-channel hydro- and morphodynamic changes modelled. We found that despite their widespread availability, hydrodynamic, morphodynamic and cellular models have yet to be used routinely in future in-channel simulations, with cellular models in particular under-represented. Our review shows that predictions of within-channel changes vary greatly between hydro-climatic regions and under contrasting climate change scenarios, mainly due to varying input discharge scenarios; however, increased sediment transport and flood risk are usually predicted. Key challenges in simulating future channel change include representations of external forcing conditions, adequate temporal and spatial scales, transport equations, changing channel materials and lateral erosion; calibration and validation; simulation chains with multiple models; and identification of feedback systems and non-linearity. Nevertheless, despite these challenges, models with increasing complexity have recently been developed and so there is increasing potential in their application. One-dimensional hydro- and morphodynamic simulations, and cellular models, can be modified to reflect the requirements of future representations, such as grain size properties, whilst there is also now an increasing capability to include a greater quantity of external forcing conditions. Some studies, however, have demonstrated the need to develop two-dimensional models for application in centennial-scale studies. We recommend that a wider range of scenarios and the combined effects of multiple external forcing factors should be included, whilst studies are also needed from more hydrologically diverse reaches.