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Validation of 40 year multimodel seasonal precipitation forecasts: The role of ENSO on the global skill

Journal: Journal of Geophysical Research - Atmospheres
Year: 2014  
Status: Published
PDF file: 2014_Manzanas_JGR.pdf
Link to PDF: Online paper
DOI: 10.1002/2013JD020680

The skill of seasonal precipitation forecasts is assessed worldwide -grid point by grid point- for the 40 year period 1961-2000, considering the ENSEMBLES multimodel hindcast and applying a tercile-based probabilistic approach in terms of the ROC Skill Score (ROCSS). Although predictability varies with region, season and lead-time, results indicate that 1) significant skill is mainly located in the tropics -20 to 40% of the total land areas,- 2) overall, SON (MAM) is the most (least) skillful season, and 3) the skill weakens (with respect to the one-month lead case) at four-month lead -especially in JJA,- although the ROCSS spatial patterns are broadly preserved -particularly in northern South America and the Malay archipelago.-
The contribution of ENSO events to this forty-year skill is also analyzed, based on the idea that the seasonal predictability may be mainly driven by El Niño and La Niña precipitation teleconnections and, consequently, limited by the ability of the different seasonal forecasting models to accurately reproduce them. Results show that the ROCSS spatial patterns for 1) the full period 1961-2000 and 2) El Niño and La Niña events are highly correlated -over 0.85.- Moreover, the observed teleconnection patterns are properly simulated (predicted) -with spatial correlations around 0.8- by most of the models at both one and four months lead time.