How climate change is impacting the world's rivers

The vast majority of the Earth's water is found in the ocean. But only a fragment of the planet's water – roughly 0.01% – flows through its rivers. And without these rivers, many other sources of surface water, like lakes and wetlands, would run dry. This is becoming a problem with climate change, and it's posing a threat to humans and animals alike in varied and, sometimes, unexpected ways.

The dramatic effects of climate change aren’t a recent phenomenon. Lake Chad, shown here in 1963, 1973, 1987 and 1997, has shrunk from roughly 25,000 km2 to under 2,000 km2 over the past 60 years. Long blamed on dams and irrigation, researchers have found that its water loss also comes from fluctuating temperatures which have negatively impacted its second most important river, the Komadugu Yobe.

Lake Chad is a stark example of how climate change is forcing people to search for new sources of water and food. The region has seen a rise in tensions as farmers and cattle herders move towards richer land. But other continents just now feeling the pressure of climate change are starting to see their fish stocks unsuited to warmer waters – and their waters evaporating in the heat.

Europe is one of these places. In the summer of 2018, the mighty Rhine River went from a powerful current to a gentle stream when temperatures soared past 30C (86F) and drought left the otherwise lush, rainy habitat too low to accommodate more than one lane of shipping.

Other regions of the world are also coming to terms with what they once considered reliable water sources, like glaciers. Known as the world's water towers for their ability to reliably store large amounts of snow and ice, glaciers supply nearly 2 billion people with water. Experts fear the Himalayas, seen here, will lose a third of their volume by the end of the century.

Farmers in the Indus River Basin, pictured above, are dependent on glacier melt from the Himalayas for crops like rice and cotton. They're part of a larger river basin in South Asia, which includes the Ganges and Brahmaptura Rivers. In total, these three waterways sustain roughly 129 million farmers and a total of 900 million residents with water.

Unprecedented wildfires across the globe, as seen here in Australia, have been yet another side effect of climate change. The aftermath of the fires could prove toxic for Australia's most important watershed, the Murray-Darling water basin. Ash washed into the rivers that feed into the basin threaten to turn the water toxic for the 2.6 million Australians, not to mention many native species.

It's not just ash and sediment from wildfires that can choke up the water. Heavier rainfall associated with extreme weather in the US, has been sweeping more runoff pollution from farms, for example, into the rivers, which then carry it to the open sea. Algal blooms like this one off of the coast of New York is one result. Another result is a dead zone, or an area deprived of oxygen by pollution.

In fact, nitrogen pollution has also become a big problem for the Mississippi River, which runs through many US states. Besides a higher volume of nitrogen being washed into the water through flooding, increasingly powerful hurricanes connected to climate change are hurting the river's wetlands, which protect it from storm surges.