Research On SWAT Hydrological Modeling Based On GIServices For Web Services

In the field of environmental modeling, most algorithms of geoscientific models are so complex that the users require considerable time to learn how to use them and to prepare the complicated input data. Moreover, these geospatial modules or models are developed and used on a local machine. This situation limits the application and interoperability of geospatial algorithms or environmental models.SWAT (Soil and Water Assessment Tool) model, which was developed by United States Department of Agriculture in1994, is one of the most outstanding and representative geoscientific models. SWAT model has been widely applied in the fields of water resource and ecological environment all over the world. But there are still a lot of limits in sharing and interoperability for the model as well as its simulated result. The critical solution for these challenges is to build a Geographic Information Web Services (GIServices) platform as an interactive environment so as to allow collaborative work among researchers, information and computing equipment.Web services are self-defined independent software components accessible over the Internet with standard interfaces to describe a set of operations. The end user can invoke and execute a Web services or bind together different Web services to build their own application. Geographic Information Web services (GIServices), arised with Web services applied in GIS, are Web services that enable users to access geographic information, geoprocessing tools, and environmental models via the Internet. GIServices provide an effective solution to increase geospatial data sharing and geoprocessing interoperability. Most existing GIServices remain in the level of geospatial data and simple geospatial analytical services, so there is little research in complicated geoprocessing services and more complicated environmental models as Web services. Moreover, GIServices in hydrology are mainly concentrated in releasing data services. Therefore, to promote GIServices from data services level to models services level (e.g. SWAT model) is a cutting edge problem to be solved urgently.Aiming at above problems, this paper explored the realization mechanism to publish SWAT model as GIServices and implemented the SWAT model exposed as Web services accessed over the internet, supporting to be invoked and integrated at cross-platform and heterogeneous environment. It is a valid approach to allow researchers to invoke SWAT Web services and then execute simulation processing, or integrate them to their own applications.The main achievements of this dissertation are as follows.(1) In the basis of analyzing difference between geospatial calculations and hydrologic modeling algorithm, a design and implementation strategy for establishing models Web services for SWAT based on GIServices was proposed considering implementation methods, workflow types and transaction patterns of service chain, service granularity balance and other aspects. The design and implementation strategy consists of theoretical framework and technical framework. In the proposed process, to overcome technical challenges, such as the large amount of data required by hydrological models, complex algorithm and time-consuming execution of hydrological models and so on, should be fully taken into account in the research.(2) Relying on the theoretical and technical framework of the design and implementation strategy, SWAT was deployed to be exposed as hydrological model services named SWAT Web Services. The SWAT Web Services include ten atomic services developed using our approach, which were Watershed Delineation Service, HRU (Hydrological Response Units) Analysis Service, WeatherData Distribution Service, Snow Service, Soil Temperature Service, Evapotranspiration Service, Surface Runoff Service, Lateral Flow Service, Groundwater Flow Service and Soil Water Service.(3) A prototype WebGIS system was provided on account of free softwares to achieve SWAT simulation online by invoking SWAT Web Services, which was Hydrological Information Services and Visualization system for Mountainous Watershed of Heihe Mainstream River. The prototype system was emphasized in functionalities as follows,2D and3D visualized interaction for hydrological simulated results and geospatial information, daily spatio-temporal query for hydrological information on any HRUs and hydrological stations, geospatial data query and geospatial analysis.In conclusion, GIServices, grown along with Web services, offers effective support to increase interoperability and deep integration for SWAT model. Via released standard interfaces online, SWAT Web Services dramatically promote the accessibility, interoperability and sharing of SWAT and its outputs among different researchers. In addition, the prototype WebGIS system based on the adoption of SWAT Web services proved that the strategy for establishing SWAT Web services proposed in this research is feasible and practicable. The dynamical2D and3D geovisualized interaction implemented in the prototype system facilitate scientists in improving the understanding of hydrological processes, and daily spatio-temporal query and download of hydrological information on HRUs have enhanced the application scope of SWAT simulated results in future analysis. In summary, SWAT Web Services presented in this research is expected to become a new paradigm for GIServices in models level.