Spatio-Temporal Linkages between the North Atlantic Oscillation (NAO), Rainfall and Streamflow in Great Britain: Evidence from New Historic Datasets

The NAO is acknowledged as the primary atmospheric-oceanic teleconnection affecting British hydrometeorology. The influence of the NAO is well studied, however previous work has been conceptually, spatially and temporally limited. This work uses new historic datasets to explore linkages at a monthly scale between the North Atlantic Oscillation Index (NAOI), rainfall and streamflow in Great Britain. Rainfall (1900-2015) is analysed using UKCP18 1km gridded rainfall and the Standardised Precipitation Index (5km gridded data). Streamflow is represented using newly released modelled historic streamflow and the Standardised Streamflow Index for 293 catchments.

The rainfall analyses revealed a winter north/west and south/east divide in response to the NAO. Regions in the north/west were strongly positively correlated with the NAOI; being wetter under NAO positive (NAO+) and drier under NAO negative (NAO-). Summer is marked by a more homogenous response, however the wet/dry directionally is opposite to that under NAO+/- during winter (negative correlations between NAOI and rainfall). The streamflow analyses show similar winter patterns. NAO+ is associated with higher than normal flow in many north-western catchments, and vice versa under NAO-. Catchments in the south-east also show much lower correlations between NAOI and flow. This suggests a potential role of catchment characteristics in moderating the effect of the NAO as these catchments are underlain by aquifers which enhance their resilience to rainfall deviation. Summer flows generally show low negative correlations suggesting limited NAO influence.

In this study we demonstrate that there are significant winter linkages between monthly NAOI, rainfall and streamflow in Britain, most notably in the north/west. In summer there does appear to be some linkage between the NAOI and rainfall, although this is less distinctive than in winter. We conclude by presenting the results of a series of bivariate analyses, allowing for spatio-temporal comparisons and an integrated understanding of the water cycle linkages between the NAO, rainfall and streamflow, and in the case of the latter, the moderating/enhancing effect of local catchment characteristics.