Climate

From Multi-Year Drought To Flash Flooding: ‘Weather Whiplash’ Explained

CREDIT: AP Photo/David J. Phillip

Joselyn Ramirez swims in a flooded school playground in Houston, Tuesday, May 26, 2015. Severe weather in the Houston area overnight caused flooding.

The rapid flip from Texas’s brutal multi-year drought to devastating deluges and fatal flash floods has the media talking about “weather whiplash.” This relatively new term for a rapid switch from one type of extreme weather to another is, unfortunately, poised to become widely used in the coming decades, thanks to unrestricted carbon pollution.

In one of its best segments of the year, “‘Weather Whiplash’ Promises to Bring More Dangerous Extremes,” NBC News explains why “scientists say climate change is exacerbating the wild weather swings amid a year of historic floods, fires, tornadoes, snow and ice across the U.S.”

There are two key, related reasons why the global warming century will be one of increased weather whiplash. First, multiple studies project the normal climate for much of the United States will become moderate to severe drought. At the same time, a warming-driven moister atmosphere is already delivering more and more of the rainfall we do see in the form of deluges. That means weather whiplash.

Second, more and more observations and analyses are finding that key types of extreme weather — especially droughts and deluges — are becoming longer and stronger because of changes in our atmosphere that cause weather patterns to get “stuck.” And many studies, including a new one out Monday, ties those blocking patterns to something called “Arctic amplification,” which refers to the fact that the Arctic is warming much faster than the rest of the Northern Hemisphere (in part because of Arctic sea ice loss).

Let’s explore those both in a little more detail. The map of our drying future above comes from a February NASA study, which itself builds on a growing body of drought research. The NASA findings are unusually robust, explained the lead author: “The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at. It all showed this really, really significant drying.”

At the same time, heavy rainfall has already begun increasing over most land areas worldwide. In the last two decades in particular, U.S. scientists observed a sharp jump in the most intense two-day rainstorms, the kind we used to see only once every five years.

The 2014 National Climate Assessment (NCA), which is the definitive statement of current and future U.S. climate impacts, notes, “The mechanism driving these changes is well understood.” The congressionally-mandated report by 300 leading climate scientists and experts explains, “Warmer air can contain more water vapor than cooler air. Global analyses show that the amount of water vapor in the atmosphere has in fact increased due to human-caused warming…. This extra moisture is available to storm systems, resulting in heavier rainfalls.” The NCA, which was reviewed by the National Academy of Sciences, adds, “Climate change also alters characteristics of the atmosphere that affect weather patterns and storms.”

That final NCA point is a key one. The worst deluges have jumped not merely because warmer air holds more moisture that in turn gets sucked into major storm systems. Increasingly, scientists have explained that climate change is altering the jet stream and weather patterns in ways that can cause storm systems to slow down or get stuck, thereby giving them more time to dump heavy precipitation — or more time to dry out the ground.

The scientific literature on this is expanding rapidly. See this 2012 study on Arctic ice loss boosting the chance of extreme weather in the U.S., and this one on how changes to the jet stream drive global warming-linked extreme weather.

A new study out Monday, “Evidence linking rapid Arctic warming to mid-latitude weather patterns,” make use of “statistical tools to help identify characteristic patterns in a data set” in order to study “48 years worth of daily atmospheric information to detect weather patterns that occur repeatedly.” The researchers concluded, “As emissions of greenhouse gases continue unabated, therefore, the continued amplification of Arctic warming should favour an increased occurrence of extreme events caused by prolonged weather conditions.” And that means more of our weather will be comprised of longer, more intense droughts and longer, more intense deluges.

A 2010 Journal of Climate study found that “global warming is the main cause of a significant intensification in the North Atlantic Subtropical High (NASH) that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the southeastern United States.”

Because global warming tends to make wet areas wetter and dry areas drier, this effect does not manifest itself the same way in every part of the country. Here is the NCA chart of “percent changes in the amount of precipitation falling in very heavy events (the heaviest 1 percent) from 1958 to 2012 for each region”:

NE.Precip-638x574

CREDIT: Nation Climate Assessment 2014

Thanks to climate change, when it rains, it pours, literally. The NCA explained, “The heaviest rainfall events have become heavier and more frequent, and the amount of rain falling on the heaviest rain days has also increased.” Some 70 percent more precipitation falls in the heaviest rain events now than it did in 1958.

What this means is that even for the regions that are expected to see a drop in total annual precipitation — such as the Southwest — more of the precipitation they do get will be in the form of deluges so intense they can create terrible flash floods. And so we can expect more stories like this one from September, where Phoenix, Arizona was hit with a massive dust storm, followed by its wettest day ever record.

As for water-logged Texas, state climatologist John Nielsen-Gammon explained to the Texas Tribune last week, “We have observed an increase of heavy rain events, at least in the South-Central United States, including Texas.” Nielsen-Gammon (a Governor George W. Bush appointee), added, “And it’s consistent with what we would expect from climate change.”

Yet, a major 2012 study found “indications of an increase in frequency of low seasonal precipitation totals” in Texas. It also found that extreme heat waves in Texas, like the one that occurred in 2011, are vastly more likely to occur in certain years than they were 40 to 50 years ago. Last year, during the height of what was one of the worst droughts to hit Texas in 500 years, Nielsen-Gammon explained to one Texas newspaper that over the longer term, South Texas “could see both worse droughts and worse floods,” due to climate change.

One of the most striking instances of weather whiplash to hit this country began 10 years ago during the summer of Hurricane Katrina. While the U.S. suffered a record-smashing hurricane season that deluged southern Louisiana with rain in 2005, “the eight months since October 1, 2005 have been the driest in 111 years of record-keeping,” as the NOAA’s National Climatic Data Center reported in 2006.

Weather whiplash has also been hitting other key parts of the world. As a 2009 BBC story explained, “Experts say global warming may be behind the wild climate swings that have brought periods of unprecedented droughts and flooding to the Amazon in recent years.”

The bottom line is that scientists predicted a long time ago that climate change would increase the intensity and frequency of both the worst deluges and the worst droughts. We’re already observing that trend toward weather whiplash. Now scientists are telling us things will get a lot worse if we don’t reverse carbon pollution trends ASAP. After all, the Earth has only warmed one degree Fahrenheit in the past half-century, while we are on track to warm as much as ten times that this century if we continue ignoring the warnings.