Quantifying erosion hazards and economic damage to critical infrastructure in river catchments: Impact of a warming climate

Climate change is projected to cause considerable pressure on our environment and communities. In particular, an increase in flooding and extreme erosion events is foreseeable as a result of an anticipated increase in the frequency and severity of storms. In the absence of timely and strategic intervention, climate change is taking us closer to more uncertain (non-linear, stochastic) and potentially more catastrophic climatic impacts. This paper develops a state-of-the-art modelling framework to assess the economic impact of erosion hazards on critical infrastructure and evaluate their vulnerability and resilience to differing storm regimes. This framework is trialled on a UK town (Cockermouth, NW England) that has experienced significant storm-related erosion and flood damage in recent years, highlighting its ability to determine current and future erosion hazard to critical infrastructure. A hydro-sedimentary model is used to simulate fluvial and hillslope sediment erosion and deposition caused by extreme storms within river catchments (sheet, rill, gully and channel bank and bed erosion). The model is applied for current climate conditions and for two future epochs (2021-2040 & 2061-2080) to assess changing erosion hazard to critical infrastructure. Climate conditions for the two epochs are obtained using the UKCP18 high resolution realisation projections under emission scenario RCP8.5. The economic loss caused by these hazards is projected based on new, non-linear depth-cost curves derived from previous assessments. The results show that: 1) due to a warming climate, total rainfall in the Cockermouth area (and likely across the UK) may be higher for all storm durations and annual exceedance probabilities, until epoch 2061-2080 when the rainfall regime may shift towards shorter duration events with higher rainfall and longer duration events with less rainfall; 2) the total area that undergoes flooding, erosion and sediment deposition, and the magnitude of the hazard, may increase as the climate shifts; 3) the economic damage caused by erosion and deposition is positively related to rainfall total, and the highest costs are likely to be associated with damage caused to bridges (102-130 pound million), followed by sediment deposition in the urban fabric (9-82 pound million), and erosion damage to agricultural land (16-26 pound million), buildings (0.4-18 pound million) and roads (0.4-4 pound million); and 4) the Estimated Annual Damage costs suggest that investment in bridges (4-6 pound million) in the Cockermouth area is required now to ensure their resilience to extreme storm events, and interventions are likely to be needed within the next 20 years to prevent high economic costs associated with significant sediment deposition in the urban fabric (0.3-4 pound million) and damage to roads (0.08-0.1 pound million) and agricultural land (0.6-2 pound million). This new framework can help support operational (immediate) and strategic (medium to long term i.e. 10+ years) erosion control decision making through the provision of an assessment of the scale and consequences of erosion.