The impact of climate change on U. K. river flows: A preliminary comparison of two generations of probabilistic climate projections

Abstract

The impacts of climate change on future river flows are a growing concern. Typically, impacts are simulated by driving hydrological models with climate model ensemble data. The U.K. Climate Projections 2009 (UKCP09) provided probabilistic projections, enabling a risk-based approach to decision-making under climate change. Recently, an update was released-UKCP18-so there is a need for information on how impacts may differ. The probabilistic projections from UKCP18 and UKCP09 are here applied using the change factor method with catchment-based hydrological modelling for 10 catchments across England. Projections of changes in median, mean, high, and low flows are made for the 2050s, using the A1B emissions scenario from UKCP09 and UKCP18 as well as the RCP4.5 and RCP8.5 emissions scenarios from UCKP18. The results show that, in all catchments for all flow measures, the central estimate of change under UKCP18 is similar to that from UKCP09 (A1B emissions).However, the probabilistic uncertainty ranges from UKCP18 are, in all cases, greater than from UKCP09, despite UKCP18 having a smaller ensemble size than UKCP09.Although there are differences between the central estimates of change using UKCP18 RCP4.5, RCP8.5 and A1B emissions, there is considerable overlap in the uncertainty ranges. The results suggest that existing assessments of hydrological impacts remain relevant, though it will be necessary to evaluate sensitive decisions using the latest projections. The analysis will aid development of advice to users of current guidance based on UKCP09 and help make decisions about the prioritization of further hydrological impacts work using UKCP18, which should also apply other products from UKCP18 like the 12-km regional data. K E Y W O R D Sclimate change, hydrological impacts, probabilistic projections, rainfall-runoff, UK Climate Projections 2018, UKCP09, UKCP18

Simulation of river flow in Britain under climate change: Baseline performance and future seasonal changes

“…The UK Climate Projections 2018 (UKCP18; Lowe et al, 2018) provide an update to UKCP09, and there is a need to update corresponding simulations of potential future changes in river flows. One such update was provided by Kay et al (2020), who applied the UKCP18 Probabilistic Projections with catchment‐based models for 10 catchments in England, to look at the range of potential changes in measures of mean, median, high and low flow. The central estimates of change showed reductions in median and low flow in all catchments, with reductions in mean flow in eight catchments, and reductions in high flow in two to three catchments (depending on the emissions scenario).…”

Spatial and temporal dynamics of nitrogen exchange in an upwelling reach of a groundwater‐fed river and potential response to perturbations changing rainfall patterns under UK climate change scenarios

“…Prolonged low summer flows are projected to be interspersed with convective high‐intensity rainfall events (see Ockenden et al, 2016). A trend corroborated by Kay et al (2020) for a wider study of 10 catchments across England that included the river Eden catchment, with predicted decreases in summer rainfall of c. 5% to 22% (50th percentile values dependent on location and region) based on probabilistic projections from UKCP2009 (J. M. Murphy et al, 2009) and UKCP2018 (Lowe et al, 2018). For the Eden catchment, this was translated into future decreases in central estimates of Q95 (low flow) river flows of c. 15% (Kay et al, 2020).…”

“…Prolonged low summer flows are projected to be interspersed with convective high-intensity rainfall events (see Ockenden et al, 2016). A trend corroborated by Kay et al (2020) for a wider study of 10 catchments across England that included the river Eden catchment, with predicted decreases in summer rainfall of c. 5%…”

“…Through synthesis and new data, the broader goal is to explore potential changes to the N dynamics of groundwater‐fed river systems due to external perturbations arising from changing rainfall patterns and temperatures predicted under UK climate change scenarios. To support this goal, additional research is drawn from Kay et al (2020) who applied probabilistic climate projections based on U.K. Climate Projections 2009 and 2018 on UK river flows that were tested on a number of catchments, including the Eden, where the research reported here lies.…”

Storylines of UK drought based on the 2010–2012 event

“…The delta method is widely employed in studies projecting the impacts of climate change across UK catchments (e.g. Arnell et al 2003;Wilby and Harris 2006;Kay et al 2020). The change factor method is valuable given the cascade of uncertainty as it is based on perturbing the observed time series and does not incur the uncertainties involved with bias correction and downscaling.…”