Background
The authors write that "precipitation extremes are expected to increase in a warming climate," and, therefore, they felt it was "essential to characterize their potential changes." Before they could do so, however, it was also clearly essential that they had to know how well the models they were going to use would actually perform in this regard. And to answer this important question ...

What was done
... Toreti et al. had to evaluate how well the models' hindcasts of the past compared with actual historical precipitation records. This they did for eight high-resolution global climate models chosen from among the well-known group of Coupled Model Intercomparison Project Phase 5 (CMIP5) models, the hindcasts of which for the period1966-2005 were compared with high-resolution daily precipitation data for that period from the Euro-Mediterranean region, northern Eurasia, the Middle East, Asia, Australia and North America.

What was learned
The nine researchers report that for the tropics and subtropics, there was a "lack of reliable and consistent estimations" that they thought "might be connected with model deficiencies in the representation of organized convective systems." And in pursuing this thought, they discovered, in their words, that "the identified lack of reliability and consistency in extreme precipitation could be associated with [1] a deficiency in the representation of upward velocities that seems to introduce large differences in climate model output, [2] an underestimation of the response to global warming (Allan and Soden, 2008; O'Gorman and Schneider, 2009), as well as with [3] model difficulties in reproducing processes based on organized convective systems (Zhang, 2005; Benedict and Randall, 2007)." At the regional level they also discovered that [4] "large variability affects the estimated seasonal changes over specific areas (e.g., eastern Asia in summer)." And, most distressing of all, they noted that [5] "for some areas such as the Indian Monsoon region, where models deficiencies were also identified by Hasson et al. (2013) and Sperber et al. (2013), reliable estimation cannot be achieved," period.

What it means
After all these years, nay, after all these decades of climate model constructing and testing, there are still gross inadequacies and misrepresentations in even the world's best climate models that are so serious as to render their projections of future precipitation of less-than-adequate value.

References
Allan, R.P. and Soden, B.J. 2008. Atmospheric warming and the amplification of precipitation extremes. Science 321: 1481-1484.

Benedict, J.J. and Randall, A.D. 2007. Observed characteristics of the MJO relative to maximum rainfall. Journal of the Atmospheric Sciences 64: 2332-2354.

Hasson, S., Lucarini, V. and Pascale, S. 2013. Hydrological cycle over South and Southeast Asian river basins as simulated by PCMDI/CMIP3 experiment. Earth System Dynamics 4: 199-217.

O'Gorman, P.A. and Schneider, T. 2009. The physical basis for increases in precipitation extremes in simulations of 21st-century climate change. Proceedings of the National Academy of Sciences U.S.A. 106: 14,773-14,777.

Sperber, K.R., Annamalai, H., Kang, I.-S., Kitoh, A., Moise, A., Turner, A., Wang, B. and Zhou, T. 2013. The Asian summer monsoon: An intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century. Climate Dynamics: 10.1007/s00382-012-1607-6.

Zhang, C. 2005. Madden-Julian Oscillation. Reviews of Geophysics 43: 10.1029/2004RG000158.