Constraining the Increased Frequency of Global Precipitation Extremes Under Warming
Scientists at University of California, Los Angeles have developed an emergent constraint (EC) that can be used to reduce uncertainty in climate model projections of future heavy rainfall occurrence. The constraint reduces intermodel spread by 20-40% and suggests that historical global precipitation extremes will occur roughly 32 ± 8% more often than present by 2100 under a medium-emissions pathway (and 55 ± 13% under high-emissions).
Climate change is causing more frequent and intense precipitation extremes; however, these changes are difficult to project. Our efforts to reduce this intermodel uncertainty rely on simulations and observations of the change in heavy rainfall over the past four decades. The EC suggests that the higher-end projections are unlikely based on the observed change. If we accept the Clausius-Clapeyron explanations, which drive future changes in precipitation, our results provide another independent line of evidence that in many models, the climate sensitivity is too strong.
A key indicator of climate change is the greater frequency and intensity of precipitation extremes across much of the globe. Several studies have already documented increased regional precipitation extremes over recent decades. Future projections of these changes, however, vary widely across climate models. Using two generations of models, we demonstrate an emergent relationship between the future increased occurrence of precipitation extremes aggregated over the globe and the observable change in their frequency over recent decades. This relationship is robust in constraining frequency changes to precipitation extremes in two separate ensembles and under two future emissions pathways (reducing intermodel spread by 20-40%). Moreover, this relationship is also apparent when the analysis is limited to near-global land regions. These constraints suggest that historical global precipitation extremes will occur roughly 32 ± 8% more often than present by 2100 under a medium-emissions pathway (and 55 ± 13% under high-emissions).