Open and Free Datasets for Hydrology Research: Insights, Challenges and Opportunities

Open and free data underpin a new way of thinking about what is required to advance scientific discoveries. The fourth paradigm for hydrology, i.e. data-intensive science, can only lead to transformative science and groundbreaking findings if data is freely accessible. Open datasets are available online, are accessible in machine-readable formats (i.e. not pdfs or reports), and are obtainable by the public. Free refers to the availability of datasets  at no cost to individuals, researchers, institutions, or projects. Here, we provide a broad perspective on the current state of hydrological data including data quality, reliability, uncertainty, national and/or international data policies with a special focus on hydropolitics including current data policies. We also discuss the need for increasing awareness and improving visibility of existing datasets and dedicated projects and repositories. Crowdsourced scientific efforts enable collaborative work and provide potential solutions to these issues. We report on our work initiating a crowdsourced manuscript with an inventory of open and free hydrological datasets from around the world, providing a database of static links, data DOIs, descriptions of datasets, and the general typologies of these data including their usability, uncertainty, quality, and trustworthiness. Our work catalyzes new discussions around data requirements for advancing hydrological research.