DEMETER improves European weather forecasts
The discovery and further investigation of the El Nino Southern Oscillation (ENSO) confirmed that changes in meteorological conditions in one part of the world can influence climate at great distances. Hence, accurate weather prediction often requires a good understanding of what is happening far away from the area of interest. The DEMETER project sought to improve forecasting skill for seasonal forecasts in Europe. Seasonal forecasts play an important role in agriculture, water management, risk management and other disciplines. The DEMETER consortium achieved this end by implementing a multi-model prediction system based on seven coupled general circulation models (CGCMs). Once the system was constructed, it was tested in hindcast mode with data spanning from 1958 to 2001, ensuring that a wide range of meteorological conditions were included. In order to gauge the ability of DEMETER against its constituent CGCMs, a Central Verification System (CVS) was developed. DEMETER output and individual model output were compared against reanalysis data as well as precipitation data from the Global Precipitation Climatology Project. The CVS evaluated both probabilistic and deterministic type forecasts using a number of statistical indices such as multi-category skill scores. Maps were also constructed to indicate which model performed best in particular regions. The analysis concentrated on phenomena central to seasonal climate variation, such as ENSO and the North Atlantic Oscillation (NAO). The results of the exercise clearly show that the DEMETER multi-model prediction system outperforms any single model alone. Furthermore, major events like shifts in the ENSO or NAO signal could be accurately predicted up to six months in advance. Of particular interest was DEMETER's ability to provide dependable surface temperature forecasts one month ahead. Forecasting skill varied from region to region, with a peak in the tropical regions, though extra-tropical forecasts were good enough to merit implementation over Europe and North America. Dissemination of the CVS particulars and more information on DEMETER can be found at: http://www.ecmwf.int/research/demeter/verification/(opens in new window).
