Modelling the Impacts of Climate Change on Future Rates of Soil Erosion: Addressing Key Limitations

Abstract

Future climate change is expected to impact the extent, frequency, and magnitude of soil erosion in a variety of ways. The most direct of these impacts is the projected increase in the erosive power of rainfall owing to an increase in the moisture-holding capacity of the atmosphere, but other more indirect impacts include changes in plant biomass and shifts in land use to accommodate the new climatic regime. Given the potential for climate change to increase soil erosion and its associated adverse impacts, modelling future rates of erosion is a crucial step in its assessment as a potential future environmental problem, and as a basis to help advise future conservation strategies. In this study, the Water Erosion Prediction Project (WEPP) model is used to simulate the impacts of climate change on future rates of soil erosion for a case study hillslope in Northern Ireland for three future time periods centered on the 2020s, 2050s and 2080s. Despite the wide range of previous modelling studies, in the majority of cases a number of limitations are apparent with respect to their treatment of the direct impacts (changed climate data), and their failure to factor in the indirect impacts (changing land use and management). In addressing the need for site-specific climate change impacts, for example, many previous studies have attempted to downscale future climate change output from general circulation models (GCMs). The most popular downscaling approach in future soil erosion studies is the change factor method, yet this approach possesses severe limitations with respect to modelling future erosion rates since it incorporates only changes in the mean climate and fails to account for climate variability. In order to address this limitation, statistical downscaling methods are used in this study to downscale future climate change projections using three GCMs and two emissions scenarios, providing daily site-specific climate inputs to WEPP in a manner that incorporates both changes in the mean climate and its variability. The temporal scale of climate change projections is also a key limitation with respect to modelling future erosion rates. The most severe soil losses often occur in high intensity rainfall events that occur over very short time intervals, yet input to soil erosion models tends to be at a daily resolution. Given the decreasing confidence of future climate change projections at a sub-daily temporal resolution, a sensitivity analysis approach is used in this study to perturb the sub-daily rainfall intensity parameter in WEPP. In addition, most previous studies fail to account for the indirect impacts of climate change on soil erosion, with no change in land use and management often assumed. Here, a scenarios-based approach is employed to examine the impacts of changing crop cover and management on future rates of soil erosion. Results indicate a mix of soil erosion increases and decreases, depending on which scenarios are considered. Downscaled climate change projections in isolation generally result in erosion decreases, whereas large increases are projected when land use is changed from the current cover of grass to a row crop which requires annual tillage, and/or where large changes in sub-daily rainfall intensity are applied. The overall findings illustrate the potential for increased soil erosion under future climate change, and illuminate the need to address key limitations in previous studies with respect to the treatment of future climate change projections, and crucially, the factoring in of future land use and management.