River water quality declining worldwide as a result of climate change

 Our ability to manage water is severely threatened by climate change, more droughts, and more frequent rainstorms. Water quality as well as availability are under threat.

However, the most recent IPCC assessment claims that our current comprehension of this issue is insufficient. An international team of experts has assembled a substantial amount of research on the water quality in rivers around the world to close this gap.

According to a study published in Nature Reviews Earth & Environment, river water quality tends to decline after severe weather events. Ecosystem health and human access to clean water may be put at risk when these occurrences become more frequent and severe as a result of climate change.

The research led by Dr Michelle van Vliet of Utrecht University analysed 965 cases of river water quality changes during extreme weather such as drought, heatwaves, rainstorms, and flooding, as well as under long-term (multidecadal) changes in climate.

“We looked at various water quality constituents such as water temperature, dissolved oxygen, salinity and concentration of nutrients, metals, microorganisms, pharmaceuticals, and plastics,” said van Vliet.

The analysis shows that in most cases water quality tends to deteriorate during droughts and heatwaves (68 per cent), rainstorms and floods (51 per cent) and long-term changes in climate (56 per cent).

During droughts, less water is available to dilute contaminants, while rainstorms and floods generally result in more contaminants that run off from land to rivers and streams.

Improvements or mixed responses in water quality are also reported for some cases owing to counteracting mechanisms, for example when increased transport of pollutants is offset by more dilution during flood events.

Water quality changes are strongly driven by changes in river discharge and water temperature. Land use and other human factors such as wastewater treatment also shape how this plays out. “Understanding the complex interplay between climate, land use and human drivers, which together influence the sources and transport of pollutants is crucial,” said van Vliet.

The research also calls for more data collection and studies of water quality in non-Western countries. “We need a better monitoring of water quality in Africa and Asia. Most water quality studies now focus on rivers and streams in North America and Europe”.

The results of the study underline the urgent need for a better understanding of water quality changes during extreme weather events, and the mechanisms underlying this.

“Only then will we be able to develop effective water management strategies that can safeguard our access to clean water and ensure ecosystem health under climate change and increasing weather extremes."