06 Dec 2022
06 Dec 2022
Status: this preprint is open for discussion.

Evaluating Precipitation Distributions at Regional Scales: A Benchmarking Framework and Application to CMIP 5 and 6 Models

Min-Seop Ahn1, Paul A. Ullrich2,1, Peter J. Gleckler1, Jiwoo Lee1, Ana C. Ordonez1, and Angeline G. Pendergrass3,4 Min-Seop Ahn et al.
  • 1PCMDI, Lawrence Livermore National Laboratory, Livermore, CA, USA
  • 2Department of Land, Air and Water Resources, University of California, Davis, CA, USA
  • 3Earth and Atmospheric Science, Cornell University, Ithaca, NY, USA
  • 4National Center for Atmospheric Research, Boulder, CO, USA

Abstract. A framework for quantifying precipitation distributions at regional scales is presented and applied to CMIP 5 and 6 models. We employ the IPCC AR6 climate reference regions over land and propose refinements to the oceanic regions based on the homogeneity of precipitation distribution characteristics. The homogeneous regions are identified as heavy, moderate, and light precipitating areas by K-means clustering of IMERG precipitation frequency and amount distributions. With the global domain partitioned into 62 regions, including 46 land and 16 ocean regions, we apply 10 established precipitation distribution metrics. The collection includes metrics focused on the maximum peak, lower 10th percentile, and upper 90th percentile in precipitation amount and frequency distributions, the similarity between observed and modeled frequency distributions, an unevenness measure based on cumulative amount, average total intensity on all days with precipitation, and number of precipitating days each year. We apply our framework to 25 CMIP5 and 41 CMIP6 models, and 6 observation-based products of daily precipitation. Our results indicate that many CMIP 5 and 6 models substantially overestimate the observed light precipitation amount and frequency as well as the number of precipitating days, especially over mid-latitude regions outside of some land regions in the Americas and Eurasia. Improvement from CMIP 5 to 6 is shown in some regions, especially in mid-latitude regions, but it is not evident globally, and over the tropics most metrics point toward over degradation.

Min-Seop Ahn et al.

Status: open (until 16 Feb 2023)

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Min-Seop Ahn et al.


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Short summary
We introduce a framework for regional scale evaluation of simulated precipitation distributions with 62 climate reference regions and 10 metrics, and we apply it to evaluate CMIP5 and CMIP6 models against multiple satellite-based precipitation products. The common model biases identified in this study are mainly associated with the overestimated light precipitation and underestimated heavy precipitation. These biases persist from earlier generation models and have been little improved in CMIP6.