Assessing the wintertime NAO flavors contribution to wet/dry cycles over Western Europe across the recent past

The North Atlantic Oscillation (NAO) represents an essential large-scale pattern of utmost importance in the understanding of the wintertime climate variability over North America and Eurasia. Despite a very large number of papers have disentangled the response of regional climate to its temporal changes, only recent works suggest that the role of spatial variability of NAO (NAO flavors) also demands attention (e.g. Rousi et al., 2020). These flavors are defined as the range of positions detected for the NAO action centers, which commonly locate over Iceland (Low) and Azores (High). This work analyses 1) the behaviour of NAO flavors (based on the first empirical orthogonal function -EOF- of Sea Level Pressure field, framed in -90W/40E/20N/80N and computed for chain 30-years periods) in the NOAA-CIRES Reanalysis, and 2) precipitation observations registered in Western Europe (Vicente-Serrano et al., 2021), across the period 1851-2015. One of the main objectives of this contribution is to assess the potential links between NAO flavors and regional wet/dry cycles in the recent past. Results reveal a physically coherent response between this spatial variability of NAO and European precipitation records. Significant positive/negative anomalies of precipitation are distinguished during different NAO flavors, ranged from -40% to +30% compared to the full period average. Likewise, the changes of mean wind direction/speed at mid/low levels have been identified as a potential physical cause. Also, the complex orography contributes to the spatial differences between wet/dry regimes. It should be highlighted that those changes of precipitation have affected European societies and ecosystems. In the case of the Iberian Peninsula, the drastic/strong reduction of winter precipitation and run-off records since 1980s (Halifa-Marín et al., 2021) is attributed to an abrupt shift eastward of NAO low action center. This work thus sheds some light on the lack of knowledge about how NAO flavors contribute to the European climate variability, meanwhile it might help understanding the abrupt shifts on regional precipitation regimes.

Acknowledgments

The authors acknowledge the ECCE project (PID2020-115693RB-I00) of Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033/) and the European Regional Development Fund (ERDF/ FEDER Una manera de hacer Europa). A.H-M thanks his predoctoral contract FPU18/00824 to the Ministerio de Ciencia, Innovación y Universidades of Spain. 

References

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Vicente-Serrano, S. M., Domínguez-Castro, F., Murphy, C., Hannaford, J., Reig, F., Peña-Angulo, D., ... & El Kenawy, A.: Long‐term variability and trends in meteorological droughts in Western Europe (1851–2018), International journal of climatology, 41, E690-E717, https://doi.org/10.1002/joc.6719, 2021.