Connection between autumn Sea Surface Temperature and winter precipitation in the Iberian Peninsula Sergio Fernández-González a , Susana C. Pereira b , Amaya Castro a , Alfredo Rocha b , Roberto Fraile a, ⁎ a Department of Physics, IMARENAB, University of León, 24071 León, Spain b CESAM, Department of Physics, University of Aveiro, 3810-193 Aveiro, Portugal abstract article info Article history: Received 20 February 2014 Received in revised form 20 June 2014 Accepted 1 July 2014 Available online 8 July 2014 Keywords: Sea Surface Temperature North Atlantic Iberian Peninsula Precipitation The oceanic influence on winter precipitation in the Iberian Peninsula has been evidenced in numerous scientific papers. Large-scale forecasting models generally use variables such as Sea Surface Temperature (SST), soil mois- ture and ice cover, but they are not very accurate yet. Using observational data, this paper analyzes the influence of North Atlantic and Mediterranean SST on winter precipitation in the Iberian Peninsula between October 1951 and September 2011. First, trends of both data sets have been calculated to study their behavior during the past six decades, showing an overall increase of SST and a substantial decrease in winter precipitation in the Iberian Peninsula, except in eastern and south-eastern regions. Then, connection patterns between autumn Sea Surface Temperature Anomalies and winter precipitation have been studied to identify ocean regions that may be used as potential predictors of winter precipitation. After applying a Principal Component Analysis to cluster the informa- tion provided by the 1431 measuring points of a SST grid with a small number of variables, the Principal Compo- nents extracted were introduced into a Multiple Linear Regression algorithm in order to obtain an estimation of winter precipitation in each river basin. The validation process has shown that the algorithm explains nearly 50% of inter-annual variability of winter precipitation in the basins of the Iberian Peninsula with a strongly oceanic influence; this percentage is somewhat lower in the Mediterranean regions. © 2014 Elsevier B.V. All rights reserved. 1. Introduction In the past decades, a general decrease of winter precipitation has been observed in the Iberian Peninsula, except in the Mediterranean region (Rodrigo and Trigo, 2007; López-Bustins et al., 2008). The decline is particularly pronounced in March (del Río et al., 2005). This fact leads to a decrease of the water resources available. Winter precipitation is very important in the Iberian Peninsula because the filling of reservoirs depends heavily on the precipitation registered in this period. Many economic activities that depend directly on water resources could optimize their management if they had a medium-large scale estimation of expected precipitation. Several studies (IPCC., 2007; del Río et al., 2011) predict declines in winter precipitation in the Iberian Peninsula over the next few decades. This fact makes that precipitation forecasting with several months in advance be even more necessary, with the aim of minimizing losses in economic sectors directly linked to climate variability. Among others, the Sea Surface Temperature (SST), can act as a potential large- scale predictor of winter weather in Europe (Folland et al., 2012). The Atlantic Meridional Overturning Circulation (AMOC) leads warm and saline waters from the Tropical Atlantic to North Atlantic high latitudes where they cool and sink, forming deep and cold currents that return southwards (Ortega et al., 2012). This causes heat transport northward. Some evidence indicates that when the thermohaline circu- lation is strong, the North Atlantic is warm, and vice versa. Trouet et al. (2012) point out that an intensification of the AMOC leads to Sea Level Pressure (SLP) anomalies that induce a positive phase of the North Atlantic Oscillation (NAO), and conversely a weakening of the AMOC that induces a negative phase of the NAO. The anomalies of Atlantic Ocean SST are characterized by opposite signs in each hemisphere during a particular season (Hodson et al., 2010). This interhemispheric dipole pattern shows multi-decadal varia- tions in the AMOC, revealing itself as a potential predictor of Atlantic Multidecadal Oscillation (Knight, 2009) which is of great importance as it causes significant impacts on the American, African and Eurasian climates. Various thermodynamic processes, such as evaporation, global warming, and precipitation, depend on thermal coupling between the ocean and the atmosphere. Negative feedback that occurs in the heat Global and Planetary Change 121 (2014) 9–18 Abbreviations: AMOC, Atlantic Meridional Overturning Circulation; ERSST, Extended Reconstructed Sea Surface Temperature; KMO, Kaiser–Meyer–Olkin; MSE, Mean Square Error; MLR, Multiple Linear Regression; NAO, North Atlantic Oscillation; PA, Precipitation Anomalies; PCA, Principal Component Analysis; PCs, Principal Components; RV, Reduction of Variance; SLP, Sea Level Pressure; SST, Sea Surface Temperature; SSTA, Sea Surface Temperature Anomalies. ⁎ Corresponding author at: Departamento de Física, Facultad de CC Biológicas y Ambientales, 24071 León, Spain. Tel.: +34 987 291 543; fax: +34 987 291 945. E-mail address: roberto.fraile@unileon.es (R. Fraile). http://dx.doi.org/10.1016/j.gloplacha.2014.07.003 0921-8181/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Global and Planetary Change journal homepage: www.elsevier.com/locate/gloplacha