Forecasting the El Niño type well before the spring predictability barrier

Abstract: The El Ni~no Southern Oscillation (ENSO) is the most important driver of interannual global climate variability and can trigger extreme weather events and disasters in various parts of the globe. Depending on the region of maximal warming, El Ni~no events can be partitioned into 2 types, Eastern Pacific (EP) and Central Pacific (CP) events. The type of an El Ni~no has a major influence on its impact and can even lead to either dry or wet conditions in the same areas on the globe. Here we show that the zonal difference $\Delta T_{WP-CP}$ between the sea surface temperature anomalies (SSTA) in the equatorial western Pacific and central Pacific gives an early indication of the type of an upcoming El Ni~no: When at the end of a year, $\Delta T_{WP-CP}$ is positive, an event in the following year will be probably an EP event, otherwise a CP event. Between 1950 and present, 3/4 of the EP forecasts and all CP forecasts are correct. When combining this approach with a previously introduced climate-network approach, we obtain reliable forecasts for both the onset and the type of an event: at a lead time of about one year, 2/3 of the EP forecasts and all CP forecasts in the regarded period are correct. The combined model has considerably more predictive power than the current operational type forecasts with a mean lead time of about 1 month and should allow early mitigation measures.