Increased droughts are forcing shipping companies to abandon some of the world's main river cargo routes, warns Ann Christina Sloek-Andersen, senior director at Maersk.

More than 300 million tonnes of goods a year are typically transported by cargo riverboats on the Rhine River, which flows for almost 800 miles from Switzerland to the Netherlands, where it joins the North Sea.

Yet during the summer months of 2022, record low water levels meant some vessels were able to carry just 25% of their usual load, so as not to risk running aground on the riverbed. This caused severe delays to shipping.

Read more: Rhine River Withers to Crisis Level as Europe Craves Energy

"We carry our customers' cargo on barges wherever possible," said Sloek-Andersen, during a February 8 interview with BBC News, "because it means far less CO₂ emissions compared to trucks."

When the Rhine's levels fell last summer, Maersk said its existing partnerships with rail providers meant they were able to "jump in with extra capacity."

Rail, said Sloek-Andersen, is the preferred alternative to river as that has a similarly low CO₂ footprint, at around 20-30g of CO₂ per tonne-km per year (gCO₂e/tkm), as opposed to trucks that emit almost 140 gCO₂e/tkm.

However, she added that other companies had to switch to road freight.

And it wasn't just Europe that found itself high and dry last year. The Mississippi River is used to transport more than 500 million tonnes of freight a year, but in 2022 record low water levels were estimated to have cost $20 billion in economic damage. In China, parts of the Yangtze River, whose surrounding provinces produce 45% of the country's economic output, were closed to ships because water levels were more than 50% below average.

It comes as studies show that drought conditions are only expected to worsen in the years ahead.