With concerns about climate 'extremes' growing, water is often the focus — either too much or too little. That is no coincidence, as climate and the hydrological cycle are tightly coupled, and water is essential to ecosystems and societies. But it is not just the quantity of water that matters. So does its quality. Impaired water quality is a global and growing problem, limiting resources for drinking, domestic use, food production and recreation, as well as harming ecosystems. Cases of extreme impairment often lead to disproportionate human and ecosystem impacts. Because the most severe water-quality impacts are exacerbated by weather, climate plays a part. Yet there has been scant study of how climate will affect the occurrence of the extreme events that relate to water quality rather than quantity. We do not know how to relate water-quality extremes, their causes, their severity or their occurrence directly to changes in climate. This piece argues that it is time to plug this knowledge gap.
Record-breaking harmful algal blooms and other severe impacts are becoming more frequent. We need to understand why.