A case study investigation of summer temperature conditions at two coastal sites in the UK, and analysis of future temperatures and heat wave structures in a warming climate scenario

Using observations for two UK coastal sites <3 km from the sea, one on the West coast near the nuclear new build (NNB) site Hinkley Point C (HPC) and the other on the East coast, near the proposed NNB site Bradwell B (BRB), changes in surface two-metre temperatures are analysed. The output from a numerical model (WRF) experiment is used for a control period, 1990-1995, [Gadian et al. 2018] and for the period 2031-2036. The nested convective permitting model at a resolution of O(3km) is driven by a global channel model at a resolution of O(20km), enabling a more detailed comparison on the weather scale than is available with current climate models. Further, using the RCP8.5 warming scenario, the results are analysed. In the future scenario, there is an increase in the number of days where the summer (JJA) model temperatures exceed 25{\deg}C. There is a future warming of 1.2{\deg}C (BRB) and 1.1{\deg}C (HPC) in the mean JJA maximum daily temperatures compared with the control values and an average annual maximum daily temperature warming of 1.2{\deg}C (BRB) and 0.5{\deg}C (HPC). For the control period, the model under-predicts both the maximum and particularly the minimum temperatures. Results indicate there will be a >25% increase in the number of summer days when the maximum temperature exceeds 25{\deg}C, a 60% increase when the temperature exceeds the minimum of 13{\deg}C, (Tables 3, 4) and an increase in heat wave events per annum of greater than 10 days, [Gadian et al. 2018]. The increases in summer temperatures are larger than those predicted in the 2013 IPCC assessment [Collins et al 2013], but consistent with the maximum temperatures and increased number of hot days listed in UKCP18 [Met Office 2019(b)]. The higher resolution model results suggest that the IPCC report underestimates the increases in maximum temperatures at these locations.