River water quality shaped by land–river connectivity in a changing climate

River water quality is crucial to ecosystem health and water security, yet its deterioration under climate change is often overlooked in climate risk assessments. Here we review how climate change influences river water quality via persistent, gradual shifts and episodic, intense extreme events. Although distinct in magnitude, intensity and duration, these changes modulate the structure and hydro-biogeochemical processes on land and in rivers, hence reshaping land–river connectivity and the quality of river waters. To advance understanding of and forecasting capabilities for water quality in future climates, it is essential to perceive land and rivers as interconnected systems. It is also vital to prioritize research under climate extremes, where the dynamics of water quality often challenge existing theories and models and call for shifts in conceptual paradigms. River water quality affects water security and is expected to degrade under climate change—an issue that has garnered limited attention. Here the authors review the impacts of climate change and climate extremes on water quality, highlighting the pivotal role of land–river connectivity.