Hydrology Research Articles Are Becoming More Interdisciplinary

We used Natural Language Processing (NLP) to assess topic diversity in the abstracts of all research articles (75,000) from eighteen water science and hydrology journals published between 1991 and 2019 -- these are all water science journals with an SCI h-index > 0.9. We found that individual water science and hydrology research articles are becoming increasingly interdisciplinary in the sense that, on average, the number of sub-topics that are represented in individual articles is increasing. This is true even though the body of water science and hydrology literature as a whole is not becoming more topically diverse. These findings suggest that the National Research Council's (1991) recommendation to increase multidisciplinarity of hydrological research has been followed in the sense that individual researchers are working to make their work more interdisciplinary. Topics with the largest increases in popularity were ‘Forecasting’ and ‘Climate Change Impacts’, and topics with the largest decreases in popularity were ‘Hydraulics’, ‘Solute Transport’, and ‘Aquifers and Abstraction’. Out of the eighteen journals that we tested, Hydrological Processes, Journal of Hydrology, and Water Resources Research are the three most topically diverse journals in the discipline. We also identified topics that are becoming increasingly isolated, and could potentially benefit from integrating more with the wider hydrology discipline.