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Seasonal extreme precipitation over the United States in CMIP6: Present-day evaluation and projected changes

Presentation Date
Monday, December 14, 2020 at 4:04pm - Monday, December 14, 2020 at 4:08pm



Accurately representing the characteristics of present-day daily precipitation has been a challenge for Earth System Models, in part due to deficiencies in model resolution and physics, but is also a circumstance of a lack of consistency in gridded observation datasets. Detailed evaluation of these models is necessary for understanding the potential uncertainties in projected changes in the future. In this study, we evaluated the present-day daily precipitation characteristics of sixteen Coupled Model Intercomparison Project Phase 6 (CMIP6) models by comparing them with three gridded observation datasets, including gridded rain gauge and satellite data. We separately evaluate summer and winter precipitation over the United States (US) with a comprehensive set of extreme precipitation indices. Furthermore, a subset of these models contributing simulations to the Shared Socioeconomic Pathways 5-8.5 (SSP5-8.5) experiment is analyzed to identify robust signals of projected changes in seasonal precipitation extremes. As part of this analysis, we found a significant difference among the observations in their estimates of area-average frequency and amount distributions, and spatial patterns of the mean and extremes precipitation over the US. This presents a major challenge for model assessment, but several robust features are evident. Overall, the CMIP6 multi-model mean performs better than most individual models at capturing present-day daily precipitation distributions and extreme precipitation indices, particularly during summer in comparison to gauge-based data. Although the “standard” horizontal-resolution varies significantly across CMIP6 models, from ~0.7˚ to ~2.8˚, we find that resolution is not a good indicator of model performance. Under the SSP5-8.5 scenario, a robust projected increase in the intensity of winter precipitation across models dominates the US by the end of the 21st century, with less agreement during the summer. In particular, a robust projected amplification of heavy precipitation (e.g., maximum five-day precipitation) over the northern US is evident in winter. Meanwhile, intermodel spread is prevalent in summer projections and dry extremes have significant regional dependence.

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