Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Drought forecasting and early warning systems for water resource extremes are increasingly important tools in water resource management in Europe where increased population density and climate change are expected to place greater pressures on water supply. In this context, the North Atlantic Oscillation (NAO) is often used to indicate future water resource behaviours (including droughts) over Europe, given its dominant control on winter rainfall totals in the North Atlantic region. Recent hydroclimate research has focused on the role of multiannual periodicities in the NAO in driving low frequency behaviours in some water resources, suggesting that notable improvements to lead-times in forecasting may be possible by incorporating these multiannual relationships. However, the importance of multiannual NAO periodicities for driving water resource behaviour, and the feasibility of this relationship for indicating future droughts, has yet to be assessed in the context of known non-stationarities that are internal to the NAO and its influence on European meteorological processes. Here we quantify the timeâfrequency relationship between the NAO and a large dataset of water resources records to identify key non-stationarities that have dominated multiannual behaviour of water resource extremes over recent decades. The most dominant of these is a 7.5-year periodicity in water resource extremes since approximately 1970 but which has been diminishing since 2005. Furthermore, we show that the non-stationary relationship between the NAO and European rainfall is clearly expressed at multiannual periodicities in the water resource records assessed. These multiannual behaviours are found to have modulated historical water resource anomalies to an extent that is comparable to the projected effects of a worst-case climate change scenario. Furthermore, there is limited systematic understanding in existing atmospheric research for non-stationarities in these periodic behaviours which poses considerable implications to existing water resource forecasting and projection systems, as well as the use of these periodic behaviours as an indicator of future water resource drought.
Highlights
Our results show that the dominant mode of multiannual covariance between the NAO Index (NAOI) and UK water resources is at the ~7.5-year periodicity
This paper assesses the utility of the relationship between the NAO and water resources, at multiannual periodicities, for improving preparedness of water resource extremes in Europe
We review this relationship in the context of non-stationary dynamics within the NAO and its control on UK meteorological variables, as well as its potential impact on water resources in climate change scenarios
Summary
Oscillatory ocean-atmosphere systems (such as El Nino Southern Oscillation (ENSO), NorthAtlantic Oscillation (NAO) and Pacific Decadal Oscillation (PDO)) are known to modulate hydrometeorological processes over a large domain, often driving multiannual periodicities in hydrological records (Kuss and Gurdak, 2014; Labat, 2010; Trigo et al, 2002). A growing number of studies have identified stronger relationships between the NAOI and certain water resource variables at multiannual periodicities (Holman et al, 2011; Neves et al, 2019; Uvo et al, 2021), than at an annual scale. This is apparent where longer hydrological response times predominate (Rust et al 2021a). Rust et al (2019; 2021a) identified a similar significant 6- to 9-year cycle across a large dataset of groundwater level (59 boreholes) and streamflow (705 gauges) in the UK, which was associated with the principal periodicity of the NAO (of a similar length (Hurrell et al, 2003; Zhang et al, 2011))
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