Rivers are critical corridors that connect cities and ecosystems. When drought develops, water levels drop, making river navigation more difficult and more expensive.
In 2022, the water levels of some of the world’s largest rivers, including the Rhine in Europe and the Yangtze in China, have fallen to historic lows. The Mississippi River fell so low in Memphis, Tennessee, in mid-October that barges could not float, necessitating special dredging and water releases from reservoirs upstream to maintain channels navigable.
Conditions on the lower Mississippi could improve somewhat, thanks to the first winter rains. But as Earth scientists at the University of Memphis, we see this year’s dramatic drop in water levels as a glimpse 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 this is only true for normal water conditions. Increasing fluctuations between low and high extremes on the Mississippi River, driven by climate change, mean that typical water conditions are no longer the norm and river transportation is likely to face more backups at the future.
Huge drop in volume
Droughts tend to start when rainfall drops below normal levels. Many other factors, including temperature, wind, cloud cover and soil type in the region, influence the severity of droughts. The soil can retain water from previous months of rainfall, providing flow to rivers that delays the onset of declines downstream.
In Memphis, hot, dry weather developed in late June 2022 and continued through early fall. Warmer temperatures increased evaporation rates and decreased soil moisture, creating a flash drought that developed within weeks.
The Mississippi River watershed drains an area that covers 1.2 million square miles (3.2 million square kilometers), or more than 40% of the continental United States. This produces a huge flow, especially on the lower Mississippi, as more tributaries flow into it.
When water levels are normal, more than 500 million cubic feet (14 million cubic meters) flow through 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, as water must travel long distances to reach the area. During the recent flash drought, however, river water levels dropped sharply from August through October, reaching an all-time low on October 20, 2022 in Memphis. The river fell 20 feet in 11 weeks.