Assessing the response of incised coastal gullies to changes in future climate: results from a Monte Carlo modelling approach

Numerical models of landscape evolution provide powerful tools to assess the impacts that environmental changes may have on landscape morphology. Under projections of future (next ~100 years) anthropogenic climate change, it is predicted that marked changes in environmental driving conditions, with relation to baseline (1961 - 1990) climates, will be experienced. Herein, a modified version of the CHILD landscape evolution model, capable of modelling coastal erosion, is employed to assess the impacts of anthropogenic climate change on the evolution of a set of incised coastal gullies found on the Isle of Wight, UK. Incised coastal gullies are known to be dynamic and sensitive landscape features which intersect the terrestrial - marine boundary; as such their evolution is influenced by changes in both terrestrial (i.e. precipitation) and maritime (i.e. sea-level and wave height) climates. To explore how these gully features might respond to future climate change, downscaled HadCM3 and CGCM2 Global Climate Model (GCM) outputs for two emissions scenarios (A2 and B2) are used to generate ensemble projections of future precipitation, sea-level and wave height. Comparison against a baseline scenario based on the 1961-1990 climatology allows for climate induced changes in system response to be quantified. To constrain the uncertainties associated with the application of landscape models and downscaled GCM data, a Monte Carlo analysis framework is employed, resulting in 17950 model runs. Results suggest that a shift towards extreme rates of coastal erosion may not be matched by equivalent changes in the rates of headwards erosion, resulting in the loss of incised coastal gully habitat on the Isle of Wight. However, under certain scenarios the possibility of extension of the gully systems exists. Therefore, considerable uncertainty surrounds such predictions, particularly in relation to the emissions scenario and GCM used. In addition, the application of a Monte Carlo methodology permits the identification of key climatic parameters responsible for causing extreme changes within these gully systems, allowing the relative importance of each climate parameter in driving incised coastal gully evolution to be assessed.