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Mediterranean Precipitation Simulated by CMIP5 Climate Models

Kelley, C., Ting, M., Seager, R. and Kushnir, Y. 2012. Mediterranean precipitation climatology, seasonal cycle, and trend as simulated by CMIP5. Geophysical Research Letters 39: 10.1029/2012GL053416.
Climate modelers have been hard at work for a very long time improving the tools of their trade; and every few years they feel obliged to report the fruits of their labors, i.e., to have their models evaluated by an independent group of colleagues, who seek to determine what advancements or improvements may - or may not - have been made. Such is the case of the present study.

In the words of authors Kelley et al. (2012), "winter and summer Mediterranean precipitation climatology and trends since 1950 as simulated by the newest generation of global climate models, the Coupled Model Intercomparison Project phase 5 (CMIP5), [were] evaluated with respect to observations and the previous generation of models (CMIP3) used in the Intergovernmental Panel on Climate Change Fourth Assessment Report," with the objective of determining "to what extent we can trust the multi-model mean (MMM) trends as representing the externally forced trends."

Upon analysis, Kelly et al. determined that "the Mediterranean precipitation trends of the last half century in the CMIP5 MMMs and the observations differ significantly, particularly in winter and over the northern Mediterranean region." The CMIP5 MMM trend, for example, "indicates a modest drying throughout the seasonal cycle, with the strongest drying in the March, April and May spring season." The observed trend, on the other hand, "shows a predominantly winter drying," and they say that "it is not entirely clear what causes this discrepancy."

Although the four researchers say "there is a modest improvement of the CMIP5 climatology over CMIP3," it would appear that even modest is too generous a word to describe what was accomplished between the development of the CMIP3 and CMIP5 models, particularly in light of the fact that they say that the slight improvement they detected may have merely been due to the "improved horizontal resolution" of the CMIP5 models.

So what is the ultimate implication of Kelly et al.'s findings? In their concluding paragraph, they say that their findings "reinforce the need for further research and better understanding of the mechanisms driving the region's hydroclimate," giving a new mandate for the world's climate modelers to do much of the same "modest" work for the next few years.

Archived 12 March 2013