Scenario-neutral approach to climate change impact studies: Application to flood risk

Abstract

This paper presents a novel framework for undertaking robust climate change impact studies, which can be used for testing the robustness of precautionary climate change allowances used in engineering design. It is illustrated with respect to fluvial flood risk in the UK. The methodology departs from conventional scenario-led impact studies because it is based on sensitivity analyses of catchment responses to a plausible range of climate changes (rather than the time-varying outcome of individual scenarios), making it scenarioneutral. The method involves separating the climate change projections (the hazard) from the catchment responsiveness (the vulnerability) expressed as changes in peak flows. By combining current understanding of likelihood of the climate change hazard with knowledge of the sensitivity of a given catchment, it is possible to evaluate the fraction of climate model projections that would not be accommodated by specified safety margins. This enables rapid appraisal of existing or new precautionary allowances for a set of climate change projections, but also for any new set of climate change projections for example arising from a new generation of climate models as soon as they are available, or when focusing on a different planning time horizon, without the need for undertaking a new climate change impact analysis with the new scenarios. The approach is demonstrated via an assessment of the UK Government's 20% allowance for climate change applied in two contrasting catchments. In these exemplars, the allowance defends against the majority of sampled climate projections for the 2080s from the IPCC-AR4 GCM and UKCP09 RCM runs but it is still possible to identify a subset of regional scenarios that would exceed the 20% threshold.

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

“…The result was 225 series of phytoplankton populations for each of the five phytoplankton groups and each of the five reaches. These series were subsequently combined to response surfaces (Prudhomme et al, 2010) showing the variation in mean phytoplankton concentration due to climatic alterations. This allows quantifying how the phytoplankton concentration could be affected by changing climate and understanding how the dynamics of the different phytoplankton groups might evolve with climate.…”

“…In this study, a "bottom-up", or "scenario-neutral" approach to climate change impact assessment (Prudhomme et al, 2010) was employed to evaluate the effect of climate change on phytoplankton concentrations and composition. It consists in (i) identifying sources of climatic alteration that are likely to affect the variable object of the study, (ii) applying these possible alterations to the observed climate to produce altered climatic series (usually precipitation and/or temperature), (iii) driving a mathematical model (hydrological, water quality, water systems, eco-hydrological, phytoplankton, etc.)…”

“…Nevertheless, other sources of climatic alteration may be relevant for the purpose of this study. For example, a change in precipitation seasonality, or intra-annual climate change could also be considered (Prudhomme et al, 2010) to evaluate the variations in peak discharge of two catchments in the UK, as a shift in raining season could affect soil moisture and therefore the hydrological cycle. Although seasonality of precipitation is less relevant than other factors such as a shift in average temperature or total precipitation, it can be an important factor affecting phytoplankton growth and phenology too, adding a third dimension to the response surfaces.…”

“…The River Thames (UK) case study was chosen because of its high relevance for water supply to fourteen million people and as a wastewater recipient from almost four million inhabitants (Kinniburgh and Barnett, 2009). In this study, we adapted the "bottom-up"-type scenarioneutral approach (Prudhomme et al, 2010) to assess the impact of climate change, land-use change and phosphorus reduction strategies on phytoplankton biomass and community composition. This approach consists in an analysis of the model sensitivity to climatic stressors, such as precipitation and temperature.…”

Climate change and river flooding: Part 2 sensitivity characterisation for british catchments and example vulnerability assessments

“…Recently, a scenario-neutral framework was developed to assess the sensitivity of flood peaks to climate change in Britain (Prudhomme et al, 2010), using a sensitivity domain comprising 4200 combinations of changes in precipitation (P), temperature (T) and potential evapotranspiration (PE). In part 1 (Prudhomme et al, submitted)this sensitivity framework was applied to 154 catchments using hydrological modelling, resulting in flood response surfaces illustrating changes in 2-, 10-and 20-year return period flood peaks for each catchment (Prudhomme et al., submitted, Section 2.4).…”