eWaterCycle V2: enabling Hydrology as a Service (HaaS)

2024 marks the 10th anniversary of presenting eWaterCycle at EGU i. Over the past decade, we've been building a platform capable of running global hydrological simulations, that democratizes research, and fosters reproducibility ii. We've built various libraries, added models, and glued them together. Our efforts culminated in the release of eWaterCycle V1 in 2021iii. ForeWaterCycle V1 we initially targeted users of hydrological models, enabling researchers and students to do experiments that they would not have been able to do before. While this narrow focus was great for designing the core functionality of the platform, the processforadding or upgrading supported models was still tedious. Model developers had to make changes to the core of eWaterCycle whenever they updated their model. To address this, we have recently released a new version of the eWaterCycle Python package that connects all components of the platform. In V2, compatibility with existing models is facilitated through a plugin structure. In contrast to eWaterCycle V1, plugins are small, simple, and self-contained, and can easily be maintained by the model owners. This structure also facilitates gradual adoption of standards until the compatibility layer becomes obsolete. Another improvement in eWaterCycle V2 is that it is now possible to run certain BMI models without containers. The use without containers, on the other hand, enables new use cases for purposes like education. While we recognize that this facilitates the development process, we still emphasize the use of containers for sharing and reproducibility. The changes in V2 make eWaterCycle simpler and more robust and facilitate a better governance structure for developing and maintaining the platform and contributed models, enabling what we envision for Hydrology as a Service:infrastructure providers host instances of the eWaterCycle platform, model developers can register their model to make it available on these platforms, and researchers can access and use them. i https://ui.adsabs.harvard.edu/abs/2014EGUGA..16.6291V ii https://doi.org/10.1002/2017WR020665 iii https://doi.org/10.5194/gmd-15-5371-2022