- The frequency of large rainfall events is currently limited by physical balances in the atmosphere, according to David Neelin of the University of California, Los Angeles, the study’s lead author.
- Neelin and team concluded that if temperatures rise by three degrees Celsius above pre-industrial averages, the probability of the largest regional precipitation events observed in the past occurring again increase as much as tenfold in most regions.
- That means that, by the end of the century, accumulation of rainwater could pose a serious challenge to human infrastructure — as well as mankind’s ability to adapt to the changing climate.
How much rain can we expect as global warming heats up the planet?
Rainfall is expected to become more intense as global temperatures continue to rise, but how the duration of any given rainfall event might be impacted is still not clear.
A study published last month in the Proceedings of the National Academy of Sciences (PNAS) sheds new light on that question, however. The study looked at precipitation accumulation, or the amount of precipitation in any single rainfall event, and found that the largest regional precipitation events are likely to become exponentially more frequent due to global warming and the increases in atmospheric moisture content that it will bring.
The frequency of large rainfall events is currently limited by physical balances in the atmosphere, according to David Neelin of the University of California, Los Angeles, the study’s lead author. Neelin and his colleagues used a global climate model and statistical theory to analyze potential changes to the upper limit of water accumulated in individual rainfall events as climate change drives average global temperatures higher.
“The study got started when we were trying to understand the probability of large events versus small events in observations,” Neelin told Mongabay. “Once we got some insight into the physical balances controlling the probability of the largest accumulations, we realized these balances imply that the accumulation size at which the probability drops quickly in current climate will extend in future climate.”
In other words, the largest rainstorms, which are currently less likely because of atmospheric conditions that restrict their probability of forming, will become far more common.
The researchers used a large supercomputer model of weather and climate maintained at the National Center for Atmospheric research in Boulder, Colorado to run simulations of weather variations under recent climate conditions as well as under conditions in which atmospheric greenhouse gas levels have increased in line with projections for the end of the century that assume manmade emissions have not been curbed.
“Indeed we found that the probabilities of the very largest accumulations increased in just the way we had predicted,” Neelin said. The researchers concluded that if temperatures rise by three degrees Celsius above pre-industrial averages, the probability of the largest regional precipitation events observed in the past occurring again increase as much as tenfold in most regions.
That means that, by the end of the century, accumulation of rainwater could pose a serious challenge to human infrastructure — as well as mankind’s ability to adapt to the changing climate.
A number of studies have looked at changes in precipitation extremes under warming and found that increases in precipitation rates were likely, the authors of the present study note. But the question remained as to whether higher precipitation rates might lead to shorter events, leaving rainfall accumulations unchanged, or if accumulations would increase as well, leading to more frequent rainfall events of the same duration that are simply more intense.
“This study indicates that we should expect the accumulations to increase as well,” Neelin said. What’s more, he adds, the increase occurs disproportionately in the probabilities of the very largest sizes of accumulations experienced by any given region.
“To visualize the impacts, just think of the precipitation event with the largest accumulation that’s occurred historically in your favorite region,” Neelin said. “Then consider that happening 2.5 to 10 times as often. Humans can adapt their infrastructure to more frequent large events, given good planning and sufficient resources. Or, if greenhouse gas emissions are reduced over the coming decades, then the changes simulated here would also be reduced.”
- Neelin, J. D., Sahany, S., Stechmann, S. N., & Bernstein, D. N. (2017). Global warming precipitation accumulation increases above the current-climate cutoff scale. Proceedings of the National Academy of Sciences, 201615333. doi:10.1073/pnas.1615333114
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