Towards a sustainable utilization of the global hydrological modelling software WaterGAP

WaterGAP是一个全球尺度的水文模拟软件，用于量化地球各大洲的水流量和储存量。它用于评估人类和非人类生物区系的水供应和水压力。在许多研究中，WaterGAP被用于模拟气候变化对灌溉用水需求、与生态有关的水流特征、地下水补给和水资源的影响;模拟结果被纳入气专委的报告。WaterGAP在全球水文模型中发挥着主导作用。然而，经过20多年来许多博士和博士后研究人员的修改，研究软件仍处于原型状态。它从来没有被重构以适应精心计划的软件架构，软件文档也非常有限。该软件类似于一个“类脚本”文件的集合，每个文件都有近10，000行代码，没有任何分离的关注点。因此，目前不可能将软件交给其他团体的研究人员来复制和理解结果，或将产品扩展到他们自己的研究中。即使是模型的改进和扩展，我们的团队也很困难。由于全球水文模型的复杂性以及与水资源有关的评估和预测的重要性，因此必须拥有能够重现结果的高质量研究软件。该项目的目标是使用现代编程语言并提供大量文档，以模块化结构重写软件。此外，代码应该允许灵活地改变WaterGAP的空间分辨率。由此产生的软件是可测试的，可维护的，可扩展的，可用的和彻底的测试，同时保持当前的计算性能。重写将使用一种适应性的方法来完成，同时按照IEEE标准1016-2009设计软件架构。将采用若干方法确保内部和外部质量管理，并增加由此产生的软件产品的外部使用。然后，其他研究人员可以自己运行我们的全球水文建模软件，复制我们的结果或调查数据和算法修改对结果的影响。研究界可以比较算法，检查我们的计算方法的一致性和准确性，并更容易地发现软件中可能存在的错误。为了快速可靠地报告此类错误，我们打算使用github进行协作，自动化测试和基准测试。这不仅使其他人能够更有效地使用研究软件，使科学结果更可靠;可扩展和可维护的软件还可以使新研究人员花费更少的时间来理解代码和编写新代码，从而实现更快的科学进步。

WaterGAP is a global-scale hydrological simulation software that is for quantifying water flows and storages on all continents of the Earth. It is used for assessing water availability and water stress for both humans and non-human biota. In numerous studies, WaterGAP was applied to simulate the impact of climate change on e.g. irrigation water requirements, ecologically-relevant streamflow characteristics, groundwater recharge and water resources; simulation results were included in IPCC reports. WaterGAP has a leading role among global hydrological models. However, the research software, which has been modified by many PhD and postdoc researchers over more than 20 years, is still in a prototype state. It has never been refactored to fit a carefully planned software architecture and software documentation is very limited. The software resembles a collection of “script-like” files that each have close to 10,000 lines of code without any separation of concerns. It is therefore currently not possible to hand the software to researchers from other groups to replicate and understand the results or to extend the product for their own research. Even model improvements and extension by our groups are difficult. Due to the complexity of global hydrological models and the importance of the assessments and projections related to water resources it is essential to have research software that is of a quality that enables the reproducibility of results. The project goal is to rewrite the software with a modular structure using a modern programming language and providing extensive documentation. Additionally, the code should allow to flexibly change the spatial resolution of WaterGAP. The resulting software is to be testable, maintainable, extensible, and usable and thoroughly tested while maintaining the current computational performance. Rewriting will be done using an adapted scrum method, while designing the software architecture following the IEEE standard 1016-2009. A number of methods will be used to ensure internal and external quality management and to increase external usage of the resulting software product. Then, it will be possible for other researchers to run our global hydrological modelling software by themselves, to reproduce our results or investigate the impact of data and algorithm modifications on the results. The research community can compare algorithms, check the consistency and accuracy of our computational approach and find possible errors in the software more easily. For a quick and reliable reporting of such errors, we intent to make use of github for collaboration, automated testing and benchmark scenarios. This will not only enable others to use the research software more efficiently and make scientific results more reliable; a software that is extensible and maintainable also enables quicker scientific advances as new researchers spend less time understanding the code and writing new code.