Bridging multi-annual to seasonal forecasts to develop seamless information for climate extremes: frost risk application

Abstract We propose a new temporal merging method for seamless climate forecast information of climate extremes. In order to construct stable and seamless climate forecast information for user-oriented climate extremes, ensemble members are pooled across available start dates using relative weights, for a target season. Recently, vineyard farmers from Catalonia, Spain, reported frost risk during the spring months (March and April). The observations show high interannual variability of the frequency of frost days (FFD) over Catalonia for the period 1983–2022. Multi-annual to seasonal forecasts from the European Centre for Medium-Range Weather Forecasts show a varying level of FFD forecast skill for lead times 1 to 22 months. The temporally merged weighted forecast enhances forecast skill compared to individual start dates, by adding information from previous start dates, at no additional computational cost. For most start dates, the skill is primarily attributed to the warming trends, except for a few start dates, where remanent forecast skill is attributed to internal variability. The proposed anticipatory framework “Ready-Steady-Action/Go” shows that adopting seamless climate forecast information can bring about 20 to 30% potential economic value for vineyard farmers, with a maximum value noted for multi-annual forecasts.