The essential value of long‐term experimental data for hydrology and water management

Observations and data from long‐term experimental watersheds are the foundation of hydrology as a geoscience. They allow us to benchmark process understanding, observe trends and natural cycles, and are prerequisites for testing predictive models. Long‐term experimental watersheds also are places where new measurement technologies are developed. These studies offer a crucial evidence base for understanding and managing the provision of clean water supplies, predicting and mitigating the effects of floods, and protecting ecosystem services provided by rivers and wetlands. They also show how to manage land and water in an integrated, sustainable way that reduces environmental and economic costs. Key Points Hydrological data collected over many decades give us the greatest insights into how the water cycle “works” and is changing Such data have proven essential in understanding and managing water supplies, floods, and other ecosystem services We need to protect long‐term studies, promote them, and make data available; their value to society increases over time