Strengths and limitations of using model simulations (UNSEEN) to assess and anticipate climate extremes beyond the observed record

Abstract:

The UNprecedented Simulated Extreme ENsemble (UNSEEN) approach is an increasingly popular method that exploits seasonal prediction systems to assess and anticipate climate extremes beyond the observed record. UNSEEN uses pooled forecasts as plausible alternate realities. Instead of the 'single realization' of reality, pooled forecasts can be exploited to generate a larger data sample and better assess the likelihood of infrequent events, which only have a limited chance of occurring in observed records. This method has, for example, been used to improve design levels of storm-surges in the river Rhine and to anticipate and understand heatwaves in China and rainfall extremes over the UK.

Here, we introduce an open and transferable UNSEEN workflow and illustrate the strengths and limitations of the approach through applications of extreme precipitation events over Norway, the UK, and the Amazon. We show the necessity of thoroughly evaluating UNSEEN extremes and provide a framework to assess the independence, stability, and fidelity. We highlight the potential for reducing uncertainty of extreme value estimates and for detecting and attributing decadal changes in 100-year events.