Record lows on the Mississippi: How climate change is altering large rivers

Rivers are critical corridors that connect cities and ecosystems alike. When drought develops, water levels fall, making river navigation harder and more expensive.

In 2022, water levels in some of the world’s largest rivers, including the Rhine in Europe and the Yangtze in China, fell to historically low levels. The Mississippi River fell so low in Memphis, Tennessee, in mid-October that barges were unable to float, requiring dredging and special water releases from upstream reservoirs to keep channels navigable.

Conditions on the lower Mississippi may be easing somewhat, thanks to early winter rains. But as Earth scientists at the University of Memphis, we see this year’s dramatic plunge in water levels as a preview of a climate-altered future.

River barges are an efficient way to transport bulk commodities, such as grain shipments, and heavy equipment over long distances. But that’s true only for normal water conditions. Increased swings between extreme lows and highs on the Mississippi River, driven by climate change, mean that typical water conditions are no longer the norm, and that river transport is likely to face more backups in the future.

A huge decrease in volume

Droughts tend to begin when precipitation drops below normal levels. Many other factors, including temperature, wind, cloudiness, and soil type in the region, influence how severe droughts become. Soil can hold water from previous months of precipitation, providing flow to rivers that delays the onset of declines downstream.

In Memphis, hot, dry weather developed in late June 2022 and continued into the early fall. Hotter temperatures increased evaporation rates and decreased soil moisture, creating a flash drought—one that developed within weeks.

The Mississippi River’s watershed drains an area that covers 1.2 million square miles (3.2 million square kilometers)—more than 40 percent of the continental US. This produces a huge flow, especially on the lower Mississippi as more tributaries empty into it.

When water levels are normal, more than 500 million cubic feet (14 million cubic meters) flow past Memphis every second. That’s enough to fill the Rose Bowl stadium in Pasadena, California, 25 times.

Stream flow in the lower Mississippi can be slow to respond to changes in precipitation, since water must travel long distances to reach the region. During the recent flash drought, however, water levels in the river declined sharply from August into October, reaching a historic low on October 20, 2022, at Memphis. The river fell by 20 feet over 11 weeks.