A multimodel ensemble-based system for seasonal-to-interannual prediction has been developed in a joint European project known as DEMETER (Development of a European Multi-Model Ensemble System for Seasonal to Interannual Prediction). The DEMETER system comprises seven global coupled atmosphere–ocean models, each running from an ensemble of initial conditions. Comprehensive hindcast evaluation demonstrates the enhanced reliability and skill of the multimodel ensemble over a more conventional single-model ensemble approach. In addition, applications of seasonal ensemble forecasts have been incorporated into the DEMETER system. As an example of this innovative end-to-end system strategy, the use of DEMETER data in malaria forecasting processes is discussed. The strategy followed in DEMETER deals with important problems such as communication across disciplines, downscaling of climate simulations, and use of probabilistic forecast information. This illustrates the economic value of seasonal-to-interannual prediction for society as a whole.

Introduction

Seasonal-timescale climate predictions are now made routinely at a number of operational meteorological centres around the world, using comprehensive coupled models of the atmosphere, oceans, and land surface (Stockdale et al., 1998; Mason et al., 1999; Alves et al., 2002; Kanamitsu et al., 2002). They are clearly of value to a wide cross-section of society, for personal, commercial and humanitarian reasons (Thomson et al., 2000; Hartmann et al., 2002b). However, the successful transition from research activity to full operational practice has led some potential users of seasonal forecasts to have unrealistic expectations of what is practicable (‘We are getting married in six months time – should we order a marquee for the wedding reception, or will it be dry that day?’).