Predicting rainfall: climate models flawed

More likely over drier soils

A new paper in Nature reveals that afternoon storms are more likely over dry soils as opposed to soils that were moist, calling into question climate models that predict increasing drought with rising temperatures.

The paper provides evidence that rather than drier soil increasing drought, by having less moisture available for evaporation and precipitation, it actually increases the likelihood of convective rainfall.

The abstract highlights the fact that current climate models incorrectly represent this relationship:

We find no evidence in our analysis of a positive feedback—that is, a preference for rain over wetter soils—at the spatial scale (50–100 kilometres) studied. In contrast, we find that a positive feedback of soil moisture on simulated precipitation does dominate in six state-of-the-art global weather and climate models—a difference that may contribute to excessive simulated droughts in large-scale models. (source)

Associate Professor Stewart Franks, a hydrologist at the University of Newcastle and president of the International Commission on the Coupled Land Atmosphere System (ICCLAS), comments on the paper:

“The study is important in that it demonstrates yet again that when we scrutinise the models against the observations, the models fail to simulate reality. The climate models represent the interactions between the land surface and the atmosphere in only a very crude way. The exchange of moisture and energy between the land and the atmosphere is represented by a single ‘big leaf’ over areas the size of 400x400kms. What this means is that the small-scale physics of rainfall generation, especially by well-known convective processes, are entirely missed.

The models fail to represent the large-scale drivers of global climate variability such as the El Nino – Southern Oscillation (ENSO). The models fail to represent the regional scale rainfall processes.  Given this, no-one can have any confidence in any prediction of future rainfall regimes when using climate models. Climate modellers argue that they are the best we have – that might be right, but if they don’t work, they don’t work.”

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