Development of the Climate Explorer Circulation Analogues Tool

When an extreme weather event occurs scientists may be asked if similar events have occurred in the past. If the frequency of such events have changed. If such events are becoming more intense or more persistent. And if the impacts of such events are increasing or decreasing. We present a tool that uses atmospheric circulation analogues to provide a framework to answer such questions.   

When using our analogues tool there are methodological choices that need to be considered. Extreme weather events are, by their very definition, rare, so how can we assess if the analogues are close enough to the observed event to be useful? Analogues can be calculated using spatial correlation or Euclidean distance, from sea level pressure or 500 hPa geopotential height, over different domains, and for different timescales. Investigating how sensitive results are to these choices allows us to provide a set of rules for using our tool for a range of different types of climate extremes, from heatwaves to extreme rainfall. 

Through a series of case studies, we consider the methodological choices required when assessing analogues, and assess which events are most suited to analogues methods.