Scientists Predict Rain Storm Increase

A new study published late last month in the journal Nature Climate Change found that the volume of rainfall from massive storms known as mesoscale convective systems will increase by as much as 80% in the southeast by the end of this century (or whenever the temperature increase assumed in the model is reached), deluging sizable portions of states. The study builds on previous work showing that storms which have become more intense will continue to do so as the climate warms was funded by the National Science Foundation, and by the U.S. Army Corps of Engineers.

An increase in extreme precipitation is one of the expected impacts of climate change. Scientists predict that as the atmosphere warms, it will hold more water, and a wetter atmosphere can produce heavier rain. In fact, an increase in precipitation intensity has already been measured in some regions. The persistent rain storms over Houston in the wake of Hurricane Harvey were an example of an unusually powerful and long-lived mesoscale convective storm system.

These clusters of thunderstorms that can extend for many dozens of miles and last for hours or in the case of Houston days, producing flash floods, debris flows, landslides, high winds, and/or hail. The current study uses a high-resolution computer simulations of current and predicted weather, in a future with a climate that was 5 degrees Celsius (9 degrees Fahrenheit) warmer that the scientists build last year.

The increase in temperature assumed in the model is significantly higher than the “best estimate temperature” increase expected by the Intergovernmental Panel on Climate Change (IPCC). The IPCC projected temperature for seven scenarios. Across all the scenarios they found a “best estimate temperature” increase range of 0.6-4.0 degrees Celsius by the end of the century.

Nonetheless, in the new study, Prein and his co-authors focused on storms that cause major summertime flooding east of the Continental Divide. They investigated not only how their rainfall intensity will change in a future climate that was 5 degrees Celsius, but also how their size, movement, and rainfall volume may evolve.

Dr. Prein and his co-authors looked at how storms that occurred between 2000 and 2013 might change if they occurred instead in a climate that was 5 degrees Celsius (9 degrees Fahrenheit) warmer. They found, for example, that intense mesoscale convective systems (MCSs) storms over an area the size of New York City could drop 60% more rain than a severe present-day system.

"This is a warning signal that says the floods of the future are likely to be much greater than what our current infrastructure is designed for," Dr. Prein said in a news release. "If you have a slow-moving storm system that aligns over a densely populated area, the result can be devastating, as could be seen in the impact of Hurricane Harvey on Houston."

Dr. Prein cautioned that this approach is a simplified way of comparing present and future climate. It doesn't reflect possible changes to storm tracks or weather systems associated with climate change and only looks at a future where the temperature increase is 5 degrees Celsius. The advantage, however, is that scientists can more easily isolate the impact of additional heat and associated moisture on future storm formation.

 

The assumptions may be aggressive, but the message you should take away is that as a nation our infrastructure has not only been inadequately maintained, but it was simply not designed for the kind of massive rain storm volume that the scientists are projecting. We need to be ready for what the future brings. 

Title: Increased rainfall volume from future convective storms in the US
Authors: Andreas F Prein, Changhai Liu, Kyoko Ikeda, Stanley B Trier, Roy M Rasmussen, Greg J Holland, Martyn P Clark
Journal: Nature Climate Change