David Maidment
July, 2007
Hydrologic Information System
The need to make hydrologic information more widely available has long been recognized as a priority among the hydrologic research community. National datasets combined with regional and local observatory datasets offer the potential to investigate hydrologic science in more depth than ever before. However, not all sources of hydrologic data are readily available. Sources that are available are often stored in incompatible formats such that significant difficulty exists in merging these datasets into a common table or database. One method of dissemination of hydrologic data is a Hydrologic Information System (HIS).
The Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) is a coalition of over one hundred universities organized to develop infrastructure and services for the advancement of hydrologic science, and is funded by the National Science Foundation. One of the multiple programs developed by CUAHSI is a national HIS (http://www.cuahsi.org/his). The goal of an HIS is to provide a venue for hydrologic data discovery, delivery, and publication. Similar efforts are being conducted at regional scales to make regional and local data available. While an “enterprise” HIS can be created at larger scales, similar “workgroup” HIS can be developed within a research group to share data in a consistent format. The idea of an HIS encompasses multiple emerging tools and technologies including Webservices, OpenMI and an Observations Data Model. See below for brief descriptions and the accompanying documents for more in-depth tutorials and examples of these exciting advances in hydrology.
Figure 1: The Concept of a Hydrologic Information System
Web Services
HIS web services are designed to scour a given repository (USGS National Water Information System, EPA Storet, NCDC Automated Surface Observing System, AmeriFlux, Daymet etc.) for a desired subset of data and return the data to the user in a format (i.e. xml) that can be ingested into a variety of applications, such as Microsoft Excel, Matlab and ArcGIS. These web services allow an individual investigator to access multiple sources of hydrologic data in an simple and easy manner, satisfying the HIS goals of providing a venue for data discovery and delivery. See Web Services for more information. CUAHSI has developed an XML markup language called WaterML for describing observations of water conditions (precipitation, streamflow, water quality, groundwater levels) collected at point locations. WaterML has been submitted to the Open GIS Consortium for review and reconciliation with existing OGC standards for XML data communication. WaterML has an associated set of web services called WaterOneFlow which perform particular data access functions (GetSites, GetVariables, GetSiteInfo, GetVariableInfo, GetValues).
Observations Data Model
The goal of a HIS is to make comprehensive hydrologic information from multiple scales available in a format that is easy to use. The Observations Data Model (ODM) has been developed as a universal data structure in which to store observations data, and has greatly assisted the creation of a HIS. At the time of publication for this tutorial, the ODM had been developed through several preliminary versions and a Version 1.0 See the accompanying document “CUAHSI Community Observations Data Model Working Design Specifications Document” by Tarboton, Horsburgh, and Maidment for a more in depth description of this model and its specifications.
Figure 2: Observations Data Model v. 3.0 Schema: a universal data structure
The strength of the ODM is derived from the fact that a single database structure can be used for various sources of data. Because this data is stored within the same structure, data from multiple sources can be merged and treated as a single source.
OpenMI
OpenMI (short for Open Model Integration Environment) is a data and model integration framework. The primary objective is to take otherwise independent data and computing systems, for example a database storing rainfall time series, a rainfall-runoff model, and a river hydraulics model, and provide a standard means for describing how time series are communicated between the systems. See OpenMI for more information.