The Mississippi River during a drought, January 2013. USDA
Bouts of intense rainfall and drought are hurting water quality in rivers around the globe, according to a sprawling new analysis.
For the study, scientists looked at 965 case studies, tracking how extreme weather impacted rivers on every habitable continent. They found that water quality dropped during 51 percent of rainstorms and floods, as fertilizer runoff poured into rivers and streams.
Water quality fell during 68 percent of droughts and heat waves. While a drop in flow meant there was less runoff, it also meant there was less water available to dilute contamination, including from pharmaceuticals found in wastewater. Overheated rivers also saw oxygen levels decline.
Over the long term, the study found, warming rivers are generally seeing pollution levels rise and oxygen levels drop. The findings, published in Nature Reviews Earth & Environment, are based largely on data from Western nations. Authors say there is still a dearth of data on the developing world.
“We need a better monitoring of water quality in Africa and Asia,” lead author Michelle van Vliet, of Utrecht University, said in a statement. “Most water quality studies now focus on rivers and streams in North America and Europe.”
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