Complex cycling workflows are fundamental to numerical weather prediction (NWP) and related environmental forecasting systems. Large numbers of jobs are executed at regular intervals to process new data and generate new forecasts. Dependence between these forecast cycles creates a single never-ending workflow, but NWP workflow schedulers have traditionally ignored this-at the cost of efficiency when running “off the clock”-by enforcing a simpler nonoverlapping sequence of single-cycle workflows. Cylc (“Silk”)1 -3 is designed to manage infinite cycling workflows efficiently even after delays in real-time operation, or in historical runs, when cycles can typically interleave for much-increased throughput. Cylc is not actually specialized to environmental forecasting, however, and cycling workflows may also be useful in other contexts. In this paper, we describe the origins and major features of Cylc, future plans for the project, and our experience of Open Source development and community engagement. ... Read more

The suggestions by Hutton et al. might not be enough to guarantee reproducible computational hydrology. Archiving software code and research data alone will not be enough. We add to the suggestion of Hutton et al. that hydrologists not only document their (computer) work, but that hydrologists use the latest best practices in designing research software, most notably the use of containers and open interfaces. To make sure hydrologists know of these best practices, we urge close collaboration with Research Software Engineers (RSEs). ... Read more

Water related catastrophes such as floods are putting more and more people at risk. Moreover this has a large economic impact as well. For example, in 2011 a flood in Bangkok wiped out a large number of harddrive manufacturing plants, leading to a global shortage and increase in price for a two year period. We have a decent grasp on forecasting the weather, especially on the short to medium term (a few days to a week). We have no such grasp for flood forecasting, especially not on the global scale. ... Read more

I made an oops once. When working on our global model hydrological model eWaterCycle I accidentally aggregated the files that contained information on rainfall per day into totals of rainfall per year. Our system didn’t budge and calculated the hydrological response as if a year’s worth of rain had fallen on January first. Oops. For this “what if” research we will revisit my mistake in a more controlled way and do the calculation properly. We study (and visualize on what-if.ewatercycle.org) what would happen if every place on earth would receive a year’s worth of rain on a single day, every year, on the same day. What if every place on earth suddenly had a 1-day rainy season and a 355-day dry season? ... Read more