Climate change and increases in droughts and heavy rains pose serious challenges to our water management. Not only is water supply under pressure, but so is its quality. However, according to the latest report from the Intergovernmental Panel on Climate Change (IPCC), our current understanding of this issue is insufficient.
Climate change exacerbates water quality problems, especially during extreme weather events. Effective water resources management strategies require a comprehensive understanding of the interactions between climate, land use and human activities, with greater focus on regions such as Africa and Asia.
To fill this gap, an international team of scientists brought together a wealth of research on water quality in rivers around the world. The research, published today (12 September) in Nature Reviews Earth & Environment, shows that river water quality tends to deteriorate during extreme weather events. As climate change causes these events to become more frequent and severe, ecosystem health and safe water use for humans may be increasingly threatened.
The study, led by Dr Michelle van Vliet of Utrecht University, analyzed 965 cases of changes in river water quality during extreme weather events such as droughts, heatwaves, heavy rains and floods, as well as long-term (multi-decade) climate change. "We looked at various water quality components such as water temperature, dissolved oxygen, salinity, and concentrations of nutrients, metals, microorganisms, pharmaceuticals and plastics," Van Vliet said.
The analysis shows that in most cases, water quality tends to worsen during droughts and heatwaves (68%), heavy rains and floods (51%), and long-term climate change (56%). During droughts, less water is available to dilute pollutants, while heavy rains and floods often cause more pollutants to flow from land into rivers and streams. In some cases, water quality has been reported to be improved or mixed due to offsetting mechanisms, such as during floods where increased contaminant transport is offset by greater dilution.
Changes in water quality are mainly affected by changes in river discharge and water temperature. Land use and other anthropogenic factors (such as wastewater treatment) also influence changes in water quality. "Climate, land use and anthropogenic factors jointly influence the sources and transport of pollutants, and understanding the complex interactions between them is critical," vanVliet said. "This study also calls for more data collection and research on water quality in non-Western countries. We need to better monitor water quality in Africa and Asia. Currently, most water quality research focuses on rivers and streams in North America and Europe."
The findings highlight the urgent need to better understand water quality changes during extreme weather events and the mechanisms behind them. Only in this way can we develop effective water management strategies that guarantee access to clean water and healthy ecosystems in the face of climate change and increasing extreme weather conditions.