Using maps of city analogues to display and interpret climate change scenarios and their uncertainty

Abstract. We describe a method to represent the results of climate simulation models with spatial analogues. An analogue to a city A is a city B whose climate today corresponds to A's simulated future climate. Climates were characterized and compared non-parametrically, using the 30-years distribution of three indicators: Aridity Index, Heating Degree Days and Cooling Degree Days. The level of correspondence (i.e. strength of analogy) was evaluated statistically with the two-samples Kolmogorov-Smirnov test, generalized to 3 dimensions. We looked at the climate of 12 European cities at the end of the 21st century under an A2 climate change scenario. We used two datasets produced with high-resolution regional climate simulation models from the Hadley Centre and Meteo France. As expected from the modelled warming in local climate, analogues were found in warmer regions, mostly at more southerly latitudes within Europe, although much model and scenario uncertainty remains. Climate analogues provide an intuitive way to show the possible effects of climate change on urban areas, offering a holistic approach to think about how cities might adapt to different climates. Evidence of its communication value comes from the reuse of our maps in teaching and in several European mass-media.