- Joint Program Report
Abstract: In this study, we assess the potential for future changes in the frequency of summertime heavy-to-extreme precipitation events – defined as 2” of rainfall in 3 hours – across the greater Cambridge area as a result of anthropogenic global warming. The study relies upon an “analogue method” that identifies well-resolved large scale, daily-averaged atmospheric patterns associated with the occurrence of local extreme events, and thus enables evaluating the ability of climate models to simulate conditions conducive to such extremes that occur at unresolvable spatial scales. We find that climate models from the Phase 5 of the Coupled Model Intercomparison Project (CMIP5) consistently reproduce the historical occurrence of these synoptic-scale patterns associated with the occurrence of the heavy-to-extreme precipitation events observed across the greater Cambridge area. Applying these analogues into the future across all the CMIP5 model projections, there is weak evidence of any considerable trend in the frequency of these heavy-to-extreme events out to the end of the 21st century. Furthermore, analyses that consider a strong climate-change mitigation scenario show no salient effect on the ensemble-median change as well as the interquartile and minimum-maximum ranges. Further work is warranted that considers: a more robust sampling of associated spatial patterns, rather than a pooled or average spatial pattern, to the local extreme; a more explicit treatment of the sub-daily atmospheric patterns that coincide with the local, sub-daily (i.e., 3-hour) event.