One of the significant areas of climate research right for us in the southwestern United States involves work on modeling the large (spatially and temporally) droughts that are so significant in long term human and ecosystem dynamics. These are the ones that are not just one-year whammies, but linger for decades, like the drought of the 1950s. Such droughts drain big multi-year reservoirs and dry out the landscape in ways that are significant and lasting.

The problem, as Toby Ault and colleagues note in a new Journal of Climate paper, is that the models don’t get this right:

Instrumental and paleoclimate data indicate that natural hydroclimate fluctuations tend to be more energetic at low (multidecadal to multicentury) than at high (interannual) frequencies. State-of-the-art global climate models do not capture this characteristic of hydroclimate variability, suggesting that the models underestimate the risk of future persistent droughts.

Team Ault is developing new methodologies that integrate the model results with paleoclimate data to try to overcome this problem, and the results are not encouraging:

In the US Southwest, for instance, state-of-the-art climate model projections suggest the risk of a decade-scale megadrought in the coming century is less than 50%; our analysis suggests that the risk is at least 80%, and may be higher than 90% in certain areas. The likelihood of longer lived events (> 35 years) is between 20% and 50%, and the risk of an unprecedented 50 year megadrought is non-negligible under the most severe warming scenario (5-10%).