Abstract
Climate change may significantly increase flood risk across Great Britain (GB), but there are large uncertainties in both future climatic changes and how these propagate into changing river flows. Here, the impact of climate change on the magnitude and frequency of high flows is modelled for 346 larger (> 144 km2) catchments across GB using the latest UK Climate Projections (UKCP18) and the DECIPHeR hydrological modelling framework. This study provides the first spatially consistent GB projections including both climate ensembles and hydrological model parameter uncertainties. Generally, results indicated an increase in the magnitude and frequency of high flows (Q10, Q1 and annual maximum) along the west coast of GB in the future (2050–2075), with increases in annual maximum flows of up to 65 % for west Scotland. In contrast, median flows (Q50) were projected to decrease across GB. All flow projections contained large uncertainties, and while the RCMs were the largest source of uncertainty overall, hydrological modelling uncertainties were considerable in east and south-east England. Regional variation in flow projections were found to relate to i) differences in climatic change and ii) catchment conditions during the baseline period as characterised by the runoff coefficient (mean discharge divided by mean precipitation). Importantly, increased heavy-precipitation events (defined by an increase in 99th percentile precipitation) did not always result in increased flood flows for catchments with low runoff coefficients, highlighting the varying factors leading to changes in high flows. These results provide a national overview of climate change impacts on high flows across GB, which will inform climate change adaptation, while also highlighting the need to account for uncertainty sources when modelling climate change impact on high flows.
Highlights
Climate change will likely significantly alter hydrological regimes in many parts of the world, with vast implications for water resource planning and policy (Brown et al, 2015; IPCC, 2014; Wagener et al, 2010)
These results provide a national overview of climate change impacts on high flows across Great Britain (GB), which will inform climate change adaptation, while highlighting the need to account for uncertainty sources when modelling climate change impact 30 on high flows
GB-average median precipitation is projected to decrease by 31-61% between the different regional climate model (RCM), with the only exception being in west Scotland (Figure 3a)
Summary
Climate change will likely significantly alter hydrological regimes in many parts of the world, with vast implications for water resource planning and policy (Brown et al, 2015; IPCC, 2014; Wagener et al, 2010). Projections indicate an intensification 35 of the hydrological cycle, with a warmer climate leading to more rain falling in high-intensity events (Eicker et al, 2016; Huntington, 2006; IPCC, 2014; Trenberth, 2011). This increase in the frequency and severity of extreme rainfall events is likely to increase flood risk in many regions. To guide water-related policy and decision making and to ensure adequate adaptation to future changes in flooding, we need hydrological modelling studies to help understand and quantify climate change impacts on the hydrological regime, and the uncertainties surrounding these projections (Reynard et 45 al., 2017)
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