Reducing the irreducible uncertainty in return periods of 21st-century precipitation extremes
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Internal climate variability, captured through multiple initial condition ensembles, may be comparable to the variability caused by knowledge gaps in future emissions trajectories and in the physical science basis, especially at adaptation-relevant scales and projection horizons. The relations to chaos theory, including extreme sensitivity to initial conditions, have caused the resulting variability in projections to be viewed as the irreducible uncertainty component of climate. The multiplier effect of ensembles from emissions-trajectories, multiple-models and initial-conditions contribute to the challenge. Here we show that ignoring this variability results in underestimation of precipitation extremes return periods leading to maladaptation. However, we also obtain the surprising, yet mechanistically plausible, insight that concatenating initial-condition ensembles results in reduction of hydroclimate uncertainty with tangible gains in our ability to inform adaptation.
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