Towards a sustainable utilization of the global hydrological research software WaterGAP

Global hydrological models are used for understanding, monitoring, and forecasting the global freshwater system. Their outputs provide crucial water-related information for various audiences, such as scientists and policymakers. WaterGAP is such a global hydrological model, and it has been utilized extensively to assess water scarcity for humans and ecologically relevant streamflow characteristics, considering the impacts of human water use and man-made reservoirs as well as of climate change.

The WaterGAP research software has been developed and modified by researchers with diverse programming backgrounds for over 30 years. During this time, there has been no clear-cut protocol for software development and no defined software architecture; hence the current state of the software is a collection of over a thousand lines of code with little  modularity and documentation. As a result, it is challenging for new model developers to understand the current software and improve or extend the model algorithm. Also, it is almost impossible to make the software available to other researchers (e.g., For the reproduction of research results).

Here we present ReWaterGAP, an ongoing project to redevelop WaterGAP into a sustainable research software (SRS). We define SRS as software that (1) is maintainable, (2) is extensible, (3) is flexible (adapts to user requirements), (4) has a defined software architecture, (5) has a comprehensive in-code and external documentation, and (6) is accessible (the software is licensed as Open Source with a DOI (digital object identifier) for proper attribution). The goal is to completely rewrite the software WaterGAP from scratch with a modular structure using a modern programming language and state-of-the-art software architecture, and to provide extensive documentation so that the resulting software fulfills the requirements of a SRS while maintaining good computational performance.

In our presentation, we provide insights into our ongoing reprogramming, outline milestones, and provide an overview of applied best practices from the computer science community (such as internal and external code review, test-driven development, and agile development methods). We plan to share the software development lessons we have learned along the way with the scientific community to help them improve their software.